KOMAG INC /DE/
S-3, 1999-12-17
MAGNETIC & OPTICAL RECORDING MEDIA
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       As filed with the Securities and Exchange Commission on December 17, 1999
                                                       Registration No. 333-____

================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                               ------------------

                                    FORM S-3
                             REGISTRATION STATEMENT
                        Under The Securities Act of 1933

                               ------------------

                               KOMAG, INCORPORATED
               (Exact name of registrant as specified in charter)

        Delaware                                        94-2914864
(State of incorporation)                 (I.R.S. employer identification number)

                               ------------------

                             1704 Automation Parkway
                               San Jose, CA 95141
                                 (408) 576-2000
       (Address, including zip code, and telephone number, including area
               code, of registrant's principal executive offices)

                               ------------------

                                  Thian Hoo Tan
                      President and Chief Executive Officer
                               Komag, Incorporated
                             1704 Automation Parkway
                               San Jose, CA 95131
                                 (408) 576-2000
    (Name, address, including zip code, and telephone number, including area
                          code, of agent for service)

                               ------------------

                                   Copies to:
                                 Alan K. Austin
                                  Brian C. Erb
                                 James C. Creigh
                        Wilson Sonsini Goodrich & Rosati
                               650 Page Mill Road
                               Palo Alto, CA 94304

                               ------------------

         Approximate Date of Commencement of proposed sale to public:  From time
to time after the effective date of this Registration Statement as determined by
market conditions.

                               ------------------

         If the only securities  being registered on this Form are being offered
pursuant to dividend or interest  reinvestment plans, please check the following
box. [ ]

         If any of the  securities  being  registered  on  this  Form  are to be
offered  on a  delayed  or  continuous  basis  pursuant  to Rule 415  under  the
Securities Act of 1933,  other than  securities  offered only in connection with
dividend or interest reinvestment plans, check the following box. [X]

         If this Form is filed to register additional securities for an offering
pursuant to Rule 462(b) under the Securities Act, please check the following box
and list  the  Securities  Act  registration  statement  number  of the  earlier
effective registration statement for the same offering. [ ]

         If this  Form is a  post-effective  amendment  filed  pursuant  to Rule
462(c) under the Securities Act, check the following box and list the Securities
Act  registration   statement  number  of  the  earlier  effective  registration
statement for the same offering. [ ]

         If delivery of the  prospectus  is expected to be made pursuant to Rule
434, please check the following box. [ ]

                               ------------------


<TABLE>
                                                   CALCULATION OF REGISTRATION FEE

<CAPTION>
====================================================================================================================================
                                                                       Proposed Maximum      Proposed Maximum
    Title of Each Class of Securities to be         Amount to be       Aggregate Price      Aggregate Offering       Amount of
                  Registered                         Registered          Per Unit(1)             Price(1)         Registration Fee
- ------------------------------------------------ ------------------- --------------------- --------------------- -------------------
<S>                     <C>                          <C>                   <C>                  <C>                     <C>
Common stock, par value $0.01 per share......        3,234,940             3.1875               10,311,372              2,723
====================================================================================================================================

<FN>
(1)  Estimated  solely for purposes of calculating the registration fee based on
     the  average of the high and low  prices of the Common  Stock on the Nasdaq
     National Market on December 16, 1999.
</FN>
</TABLE>


         THE REGISTRANT HEREBY AMENDS THIS  REGISTRATION  STATEMENT ON SUCH DATE
OR DATES AS MAY BE NECESSARY TO DELAY ITS  EFFECTIVE  DATE UNTIL THE  REGISTRANT
SHALL FILE A FURTHER AMENDMENT WHICH SPECIFICALLY  STATES THAT THIS REGISTRATION
STATEMENT SHALL  THEREAFTER  BECOME EFFECTIVE IN ACCORDANCE WITH SECTION 8(A) OF
THE SECURITIES ACT OR UNTIL THIS  REGISTRATION  STATEMENT SHALL BECOME EFFECTIVE
ON SUCH DATE AS THE SECURITIES AND EXCHANGE COMMISSION,  ACTING PURSUANT TO SAID
SECTION 8(A), MAY DETERMINE.


<PAGE>


THE  INFORMATION IN THIS  PROSPECTUS IS NOT COMPLETE AND MAY BE CHANGED.  WE MAY
NOT SELL  THESE  SECURITIES  UNTIL THE  REGISTRATION  STATEMENT  FILED  WITH THE
SECURITIES AND EXCHANGE COMMISSION IS EFFECTIVE. THIS PROSPECTUS IS NOT AN OFFER
TO  SELL  THESE  SECURITIES  AND IT IS NOT  SOLICITING  AN  OFFER  TO BUY  THESE
SECURITIES IN ANY STATE WHERE THE OFFER OR SALE IS NOT PERMITTED.


                              SUBJECT TO COMPLETION
                             DATED DECEMBER 17, 1999


PROSPECTUS


                                3,234,940 SHARES


                               KOMAG, INCORPORATED


                                  COMMON STOCK


         The Common Stock  offered  hereby will be sold from time to time by the
Selling Stockholder. See "Selling Stockholder." We will not receive any proceeds
from the sale of shares by the Selling  Stockholder.  We will pay certain of the
expenses of this offering;  however,  the Selling Stockholder will bear the cost
of all brokerage commissions and discounts,  if any, incurred in connection with
the sale of shares to which this Prospectus relates.

         The  Selling  Stockholder  may  offer  and sell all the  shares  in the
over-the-counter  market or on one or more exchanges, or otherwise at prices and
at terms then  prevailing or at prices related to the then current market price,
or in negotiated transactions,  or to one or more underwriters for resale to the
public.

         The Common  Stock is traded on the  Nasdaq  National  Market  under the
symbol  "KMAG." The last  reported  sale price of the Common Stock on the Nasdaq
National Market on December 16, 1999 was $3.0625 per share.

         The Securities and Exchange Commission and state securities  regulators
have  not  approved  or  disapproved  these  securities  or  determined  if this
prospectus  is truthful or  complete.  Any  representation  to the contrary is a
criminal offense.


                 The date of this prospectus is ________, 1999.


<PAGE>


                       WHERE YOU CAN FIND MORE INFORMATION

         We file annual,  quarterly and current  reports,  proxy  statements and
other  information  with the SEC.  You may read and copy any document we file at
the SEC's public reference room at 450 Fifth Street, N.W., Washington, DC 20549.
Please  call the SEC at  1-800-SEC-0330  for further  information  on the public
reference  room.  Our SEC filings are also  available  from the SEC's Website at
"http://www.sec.gov."

         The SEC allows us to "incorporate by reference" the information we file
with them,  which means that we can  disclose  important  information  to you by
referring you to those documents.  The information  incorporated by reference is
considered to be part of this  prospectus,  and  information  that we file later
with the SEC will  automatically  update  and  supersede  this  information.  We
incorporate by reference the following  documents:

         o        Our quarterly report on Form 10-Q for our fiscal quarter ended
                  October 3, 1999;

         o        Our current report on Form 8-K dated August 5, 1999;

         o        Our quarterly report on Form 10-Q for our fiscal quarter ended
                  July 4, 1999;

         o        Our current report on Form 8-K dated June 30, 1999;

         o        Our current report on Form 8-K dated April 9, 1999;

         o        Our quarterly report on Form 10-Q for our fiscal quarter ended
                  April 4, 1999;

         o        Our  annual  report on Form  10-K for our  fiscal  year  ended
                  January 3, 1999;

         o        The   description  of  our  common  stock   contained  in  our
                  registration statement on Form 8-A filed with the SEC on April
                  29, 1988; and

         o        Any future  filings  we will make with the SEC under  Sections
                  13(a), 13(c), 14 or 15(d) of the Securities Exchange Act.

         We will provide you with a copy of these  filings,  at no cost,  if you
write or telephone our Corporate Secretary at the following address:

                               Komag, Incorporated
                             1704 Automation Parkway
                               San Jose, CA 95131
                                 (408) 576-2000

         You should rely only on the information or representations  provided in
this  prospectus.  We have  authorized  no one to  provide  you  with  different
information.  We are not making an offer of these securities in any jurisdiction
where the offer is not permitted.  You should not assume that the information in
this  prospectus  is accurate as of any date other than the date on the front of
the document.



<PAGE>


                           FORWARD-LOOKING STATEMENTS

         This prospectus  contains or incorporates by reference  forward-looking
statements that involve risks and uncertainties.  Forward-looking statements can
typically  be  identified  by the use of words such as "may,"  "will,"  "could,"
"project,"   "believe,"    "anticipate,"   "expect,"   "estimate,"   "continue,"
"potential,"  "plan,"  "forecasts," and the like.  These statements  appear in a
number  of  places in this  prospectus  and  include  statements  regarding  our
intentions, plans, strategies,  beliefs or current expectations with respect to,
among other things:

         o        our financial prospects;

         o        our financing plans;

         o        trends affecting our financial condition or operating results;

         o        our strategies for growth, operations, and product development
                  and commercialization; and

         o        conditions  or trends in or factors  affecting the computer or
                  hard disk drive industry.

         Forward-looking  statements are not  guarantees of future  performance.
Forward-looking  statements  involve  risks and  uncertainties  that could cause
actual results to differ  materially  from those  anticipated.  The  information
contained or incorporated by reference in this prospectus  identifies  important
factors  that could cause such  differences.  Among the factors that could cause
actual  results to differ are the  following:  We sell a single  product  into a
market  characterized  by rapid  technological  change and sudden  shifts in the
balance between supply and demand. Further, we are dependent on a limited number
of  customers,  some of whom  also  manufacture  some or most of their own disks
internally.  Competition in the market, defined by both technology offerings and
pricing,  can be intense,  especially during times of excess available  capacity
such as has been prevalent since 1998. We have a high fixed-cost  structure that
can cause operating  results to vary dramatically with changes in product yields
and  utilization  of our  equipment  and  factories.  In addition,  our business
requires substantial investments for research and development activities and for
physical  assets such as  equipment  and  facilities  that are  dependent on our
access to financial resources. These and other risks are discussed more fully in
this prospectus and the documents  incorporated by reference in this prospectus.
We undertake no  obligation  to publicly  release the result of any revisions to
these  forward-looking  statements  that  may  be  made  to  reflect  events  or
circumstances   after  the  date  hereof  or  to  reflect  the   occurrence   of
unanticipated events.

                                      -2-

<PAGE>


                                   THE COMPANY

         Komag,  Incorporated designs,  manufactures and markets thin-film media
(disks),  the primary storage medium for digital data used in computer hard disk
drives.  We believe  we are the  world's  largest  independent  manufacturer  of
thin-film media and are well positioned as a broad-based  strategic  supplier of
choice  for the  industry's  leading  disk  drive  manufacturers.  Our  business
strategy  relies on the  combination  of  advanced  technology  and  high-volume
manufacturing.  Our products  serve the desktop and  enterprise  segments of the
disk drive  market and are used in  products  such as personal  computers,  disk
arrays,  network  file  servers and  engineering  workstations.  We  manufacture
leading-edge  disk  products  primarily  for 3-1/2  inch form  factor  hard disk
drives.

         Komag  was  organized  in 1983  and is  incorporated  in the  State  of
Delaware.  Our  principal  executive  offices  are  located  at 1704  Automation
Parkway, San Jose, California 95131 and our telephone number is (408) 576-2000.


                                 USE OF PROCEEDS

         The  Company  will not  receive  any of the  proceeds  from the sale of
shares of Common Stock. See "Selling Stockholder" and "Plan of Distribution."

                                      -3-

<PAGE>


                               SELLING STOCKHOLDER

         Western Digital Corporation (the "Selling  Stockholder") is selling all
of the 3,234,940 shares of Common Stock offered hereby. The shares being offered
by the Selling  Stockholder  were  acquired  from the  Company in a  transaction
exempt from the registration  requirements of the Securities Act by Section 4(2)
pursuant  to an Asset  Purchase  Agreement  between  the Company and the Selling
Stockholder, dated April 8, 1999.

         Pursuant to the Asset  Purchase  Agreement,  the Company has filed with
the  Commission,  under the Securities Act of 1933, a Registration  Statement on
Form S-3, of which this  Prospectus  forms a part, with respect to the resale of
the shares and has agreed to use  commercially  reasonable  efforts to keep this
Registration  Statement  effective  until  such  time as all of the  outstanding
3,234,940 shares can be sold by the Selling  Stockholder in a three-month period
in accordance with Rule 144 under the Securities Act.


                              PLAN OF DISTRIBUTION

         The Company has been advised by the Selling Stockholder that it intends
to sell all or a  portion  of the  shares  offered  hereby  from time to time in
transactions on one or more exchanges,  including the Nasdaq National Market, or
in the  over-the-counter  market  or  otherwise,  at  prices  and at terms  then
prevailing  or at  prices  related  to the then  current  market  prices,  or in
negotiated transactions. The shares may be sold by one or more of the following:
(a) a block trade in which the broker or dealer engaged will attempt to sell the
shares as agent but may  purchase and resell a portion of the block as principal
to facilitate the transaction;  (b) purchases by a broker or dealer as principal
and  resale by such  broker  or  dealer  for its own  account  pursuant  to this
Prospectus;  (c) an exchange  distribution  in accordance with the rules of such
exchange;  and (d) ordinary brokerage transactions and transactions in which the
broker solicits  purchasers.  In effecting sales,  brokers or dealers engaged by
the Selling  Stockholder may arrange for other brokers or dealers to participate
in the  resales.  The  shares  may be sold  from  time  to  time by the  Selling
Stockholder.

         In  connection  with  distributions  of the  shares or  otherwise,  the
Selling Stockholder may enter into hedging transactions with broker-dealers.  In
connection with such  transactions,  broker-dealers may engage in short sales of
the shares  registered  hereunder  in the course of hedging the  positions  they
assume  with the Selling  Stockholder.  The  Selling  Stockholder  may also sell
shares short and  redeliver  the shares to close out such short  positions.  The
Selling  Stockholder  may also  enter  into  option or other  transactions  with
broker-dealers  which  require the delivery to the  broker-dealer  of the shares
registered hereunder. The Selling Stockholder may also pledge the shares offered
hereby to a broker or dealer and upon a default  the broker or dealer may effect
sales of the shares pursuant to this Prospectus.

         Brokers,  dealers or agents  may  receive  compensation  in the form of
commissions, discounts or concessions from the Selling Stockholder in amounts to
be negotiated in connection with the sale. Such brokers or dealers and any other
participating  brokers or dealers may be deemed to be "underwriters"  within the
meaning  of the  Securities  Act in  connection  with such  sales,  and any such
commission, discount or concession may be deemed to be underwriting discounts or
commissions  under the Securities  Act. In addition,  any securities  covered by
this  Prospectus  which  qualify for sale pursuant to Rule 144 may be sold under
Rule 144 rather than pursuant to this Prospectus. There can be no assurance that
the Selling Shareholder will sell any or all of the shares offered hereunder.

                                      -4-

<PAGE>


                                  LEGAL MATTERS

         The validity of the shares offered hereby will be passed upon by Wilson
Sonsini Goodrich & Rosati, P.C., Palo Alto, California.


                                     EXPERTS

         Ernst & Young LLP, independent auditors,  have audited our consolidated
financial statements and schedule included in our Annual Report on Form 10-K for
the year ended January 3, 1999,  as set forth in their  report,  which as to the
three  years  ended  January  3,  1999 is based in part on the  reports  of Chuo
Corporation,  independent  auditors,  and which is  incorporated by reference in
this prospectus and elsewhere in the registration statement. The report of Ernst
& Young LLP contains an explanatory  paragraph describing  conditions that raise
substantial  doubt about our ability to continue as a going concern as described
in Note 1 to the consolidated financial statements. Our financial statements are
incorporated  by reference in reliance on Ernst & Young LLP's  report,  given on
their authority as experts in accounting and auditing.

                                      -5-

<PAGE>


                                     PART II

                     INFORMATION NOT REQUIRED IN PROSPECTUS

Item 14.  Other Expenses of Issuance and Distribution

         The following  table sets forth the expenses  (other than  underwriting
discounts and  commissions),  which,  other than the SEC  registration  fee, are
estimates,  payable by the Company in connection with the sale and  distribution
of the securities registered hereby:


          SEC registration fee...........................     $ 2,723
          Printing expenses..............................     $10,000
          Blue Sky fees and expenses.....................     $ 1,000
          Accountants' fees and expenses.................     $10,000
          Legal fees and expenses........................     $ 4,000
          Miscellaneous..................................     $ 2,277
                                                              -------
                            Total........................     $30,000
                                                              =======

Item 15.  Indemnification of Directors and Officers

         The Registrant's Restated Certificate of Incorporation provides that no
director of the Registrant will be personally liable to the Registrant or any of
its  stockholders  for monetary  damages  arising from the director's  breach of
fiduciary  duty.  However,  this  provision  does not apply with  respect to any
action in which the director would be liable under Section 174 of Title 8 of the
General  Corporation  Law of  Delaware,  nor does it apply  with  respect to any
liability  resulting from any transaction in which the director (i) breached his
duty of loyalty to the Registrant or its stockholders;  (ii) did not act in good
faith or, in failing to act, did not act in good faith;  (iii) acted in a manner
involving intentional misconduct or a knowing violation of law or, in failing to
act, acted in a manner involving  intentional  misconduct or a knowing violation
of law; or (iv) derived an improper personal benefit.

         Pursuant  to the  provisions  of Section  145 of the  Delaware  General
Corporation  Law, every Delaware  corporation  has power to indemnify any person
who was or is a party or is  threatened  to be made a party  to any  threatened,
pending or completed  action,  suit or proceeding (other than an action by or in
the  right  of the  corporation)  by  reason  of the  fact  that  he is or was a
director,  officer,  employee or agent of the Registrant or of any  corporation,
partnership,  joint  venture,  trust or other  enterprise for which he is or was
serving in such capacity at the request of the  Registrant,  against any and all
expenses,  judgments,  fines  and  amounts  paid in  settlement  and  reasonably
incurred by him in connection with such action, suit or proceeding. The power to
indemnify  applies  only if such  person  acted in good faith and in a manner he
reasonably  believed  to be in the best  interests,  or not  opposed to the best
interests,  of the  corporation,  and with  respect  to any  criminal  action or
proceeding, had no reasonable cause to believe his conduct was unlawful.

         The power to indemnify applies to actions brought by or in the right of
the  corporation  as well,  but only to the  extent of  defense  and  settlement
expenses and not to any  satisfaction  of a judgment or  settlement of the claim
itself,  and with the further limitation that in such actions no indemnification
shall be made in the  event of any  adjudication  of  negligence  or  misconduct
unless  the  court,  in its  discretion,  feels  that  in the  light  of all the
circumstances indemnification should apply.

         To the extent any of the  persons  referred  to in the two  immediately
preceding  paragraphs is  successful  in the defense of the actions  referred to
therein, such person is, pursuant to Section 145 of the Delaware General

                                      II-1

<PAGE>


Corporation Law,  entitled to  indemnification  as described above.  Section 145
also grants power to advance litigation  expenses upon receipt of an undertaking
to repay such advances in the event no right to  indemnification is subsequently
shown. A corporation may also obtain  insurance at its expense to protect anyone
who might be indemnified, or has a right to insist on indemnification, under the
statute.

         The Registrant  has entered into  indemnification  agreements  with its
directors and officers which provide for  indemnification  to the fullest extent
permitted by Delaware General Corporation Law, including Section 145 thereof.

         Agents,  dealers,  and  underwriters  may be entitled under  agreements
entered into with us to indemnification by us against certain civil liabilities,
including  liabilities under the Securities Act, or to contribution with respect
to payments that such agents,  dealers,  or underwriters may be required to make
with respect  thereto.  Agents,  dealers,  and underwriters may be customers of,
engage in transactions  with, or perform  services for us in the ordinary course
of business.

Item 16.  Exhibits

See Exhibit Index.

Item 17.  Undertakings

The undersigned registrant hereby undertakes:

         (1) To file, during any period in which offers or sales are being made,
a post-effective amendment to this registration statement:

                  (i) To include any prospectus  required by Section 10(a)(3) of
the Securities Act of 1933;

                  (ii) To reflect in the  prospectus any facts or events arising
after the  effective  date of this  registration  statement  (or the most recent
post-effective  amendment  hereof)  which,  individually  or in  the  aggregate,
represent a fundamental change in the information set forth in this registration
statement.  Notwithstanding the foregoing, any increase or decrease in volume of
securities  offered (if the total dollar value of  securities  offered would not
exceed that which was  registered) and any deviation from the low or high end of
the estimated  maximum offering range may be reflected in the form of prospectus
filed with the  Commission  pursuant  to Rule 424(b) if, in the  aggregate,  the
changes in volume and price  represent  no more than a 20% change in the maximum
aggregate  offering price set forth in the  "Calculation  of  Registration  Fee"
table in the effective registration statement.

                  (iii) To include any material  information with respect to the
plan of distribution not previously disclosed in this registration  statement or
any  material  change  to  such  information  in  this  registration  statement;
provided,  however,  that  paragraphs  (1)(i)  and  (1)(ii)  do not apply if the
information  required  to be  included in a  post-effective  amendment  by those
paragraphs  is  contained  in periodic  reports  filed with or  furnished to the
Commission  by the  registrant  pursuant  to Section 13 or Section  15(d) of the
Securities  Exchange  Act of 1934  that are  incorporated  by  reference  in the
registration statement.

         (2) That,  for the  purpose  of  determining  any  liability  under the
Securities Act of 1933, each such post-effective amendment shall be deemed to be
a new registration statement relating to the securities offered therein, and the
offering of such  securities at that time shall be deemed to be the initial bona
fide offering thereof.

                                      II-2

<PAGE>


         (3) To remove from registration by means of a post-effective  amendment
any of the securities being registered which remain unsold at the termination of
the offering.

         (4) The undersigned  registrant hereby undertakes that, for purposes of
determining  any liability  under the Securities Act of 1933, each filing of the
registrant's  annual  report  pursuant to Section  13(a) or Section 15(d) of the
Securities  Exchange  Act of 1934  (and,  where  applicable,  each  filing of an
employee  benefit  plan's  annual  report  pursuant  to  Section  15(d)  of  the
Securities  Exchange  Act of 1934) that is  incorporated  by  reference  in this
registration  statement  shall  be  deemed  to be a new  registration  statement
relating to the securities  offered herein,  and the offering of such securities
at that time shall be deemed to be the initial bona fide offering thereof.

         (5)  Insofar  as  indemnification  for  liabilities  arising  under the
Securities Act of 1933 may be permitted to directors,  officers and  controlling
persons of the registrant  pursuant to the foregoing  provisions,  or otherwise,
the  registrant  has been  advised  that in the  opinion of the  Securities  and
Exchange  Commission such  indemnification is against public policy as expressed
in the Act and is,  therefore,  unenforceable.  In the  event  that a claim  for
indemnification  against  such  liabilities  (other  than  the  payment  by  the
registrant of expenses  incurred or paid by a director,  officer or  controlling
person of the  registrant  in the  successful  defense  of any  action,  suit or
proceeding)  is  asserted by such  director,  officer or  controlling  person in
connection with the securities being registered,  the registrant will, unless in
the opinion of its counsel the matter has been settled by controlling precedent,
submit  to a  court  of  appropriate  jurisdiction  the  question  whether  such
indemnification  by it is against public policy as expressed in the Act and will
be governed by the final adjudication of such issue.

         (6) The undersigned registrant hereby undertakes that:

                  (1) For  purposes  of  determining  any  liability  under  the
Securities  Act of 1933,  the  information  omitted from the form of  prospectus
filed as part of this  registration  statement  in  reliance  upon Rule 430A and
contained  in a form of  prospectus  filed by the  registrant  pursuant  to Rule
424(b)(1) or (4) or 497(h) under the  Securities  Act shall be deemed to be part
of this registration statement as of the time it was declared effective.

                  (2) For the purpose of  determining  any  liability  under the
Securities Act of 1933,  each  post-effective  amendment that contains a form of
prospectus  shall be deemed to be a new registration  statement  relating to the
securities  offered  therein,  and the offering of such  securities at that time
shall be deemed to be the initial bona fide offering thereof.

                                      II-3

<PAGE>


                                   SIGNATURES

         Pursuant  to the  requirements  of the  Securities  Act  of  1933,  the
registrant certifies that it has reasonable grounds to believe that it meets all
of the requirements for filing on Form S-3 and has duly caused this Registration
Statement  to be  signed  on its  behalf  by  the  undersigned,  thereunto  duly
authorized, in the City of San Jose, State of California, on December 17, 1999.


                                               KOMAG, INCORPORATED


                                               By: /s/  Thian Hoo Tan
                                                   --------------------------
                                                   Thian Hoo Tan
                                                   President and Chief Executive
                                                   Officer


                                POWER OF ATTORNEY

         KNOW  ALL MEN BY  THESE  PRESENTS  that the  undersigned  officers  and
directors of Komag, Incorporated,  a Delaware corporation,  do hereby constitute
and  appoint  Thian Hoo Tan and  William L. Potts,  Jr.,  and each of them,  the
lawful  attorneys  and agents,  with full power and  authority to do any and all
acts and things and to execute any and all instruments  which said attorneys and
agents, and any one of them, determine may be necessary or advisable or required
to  enable  said  corporation  to comply  with the  Securities  Act of 1933,  as
amended,  and any rules or regulations or  requirements of the SEC in connection
with  this  Registration  Statement.  Without  limiting  the  generality  of the
foregoing  power  and  authority,  the  powers  granted  include  the  power and
authority to sign the names of the  undersigned  officers  and  directors in the
capacities  indicated  below  to  this  Registration  Statement,  to any and all
amendments,  both  pre-effective  and  post-effective,  and  supplements to this
Registration  Statement,  and to any and all  instruments or documents  filed as
part of or in  conjunction  with this  Registration  Statement or  amendments or
supplements  thereof,  and each of the undersigned  hereby ratifies and confirms
all that said attorneys and agents, or any of them, shall do or cause to be done
by virtue hereof. This Power of Attorney may be signed in several counterparts.

                                      II-4

<PAGE>


         IN WITNESS WHEREOF,  each of the undersigned has executed this Power of
Attorney as of the date indicated.

<TABLE>
         Pursuant to the requirements of the Securities Act of 1933, as amended,
this  Registration  Statement has been signed below by the following  persons in
the capacities and on the dates indicated.

<CAPTION>
             Signature                                   Title                                  Date
             ---------                                   -----                                  ----
<S>                                      <C>                                                 <C>
       /s/ Thian Hoo Tan
- ----------------------------------       President, Chief Executive Officer and              December 17, 1999
          Thian Hoo Tan                  Director (Principal Executive Officer)



    /s/ William L. Potts, Jr.
- ----------------------------------       Senior Vice President of Finance, Chief             December 17, 1999
       William L. Potts, Jr.             Financial Officer and Secretary
                                         (Principal Financial and Accounting Officer)


      /s/ Chris A. Eyre                  Director                                            December 17, 1999
- ----------------------------------
        Chris A. Eyre


      /s/ Irwin Federman                 Director                                            December 17, 1999
- ----------------------------------
        Irwin Federman


     /s/ George A. Neil                  Director                                            December 17, 1999
- ----------------------------------
      George A. Neil


   /s/ Michael R. Splinter               Director                                            December 17, 1999
- ----------------------------------
    Michael R. Splinter


       /s/ Anthony Sun                   Director                                            December 17, 1999
- ----------------------------------
         Anthony Sun


    /s/ Masayoshi Takebayashi            Director                                            December 17, 1999
- ----------------------------------
      Masayoshi Takebayashi
</TABLE>

                                                   II-5

<PAGE>


                                  EXHIBIT INDEX

   Exhibit No.                            Description
   -----------                            -----------
     2.1             Asset Purchase  Agreement  between Komag,  Incorporated and
                     Western   Digital   Corporation   dated   April   8,   1999
                     (incorporated  by  reference  to  Exhibit  10.1.13  to  the
                     Registrant's  Quarterly  Report on Form 10-Q for the fiscal
                     quarter ended July 4, 1999)

     4.1             Registration  Rights Agreement between Komag,  Incorporated
                     and Western Digital Corporation dated April 8, 1999

     5.1             Opinion of Wilson Sonsini Goodrich & Rosati

    23.1             Consent of Ernst & Young LLP, Independent Auditors

    23.2             Consent of Wilson  Sonsini  Goodrich & Rosati  (included in
                     Exhibit 5.1)

    23.3             Consent of Chuo Audit Corporation, Independent Accountants

    24.1             Power of Attorney (See signature page)





                                                                     Exhibit 4.1



                          REGISTRATION RIGHTS AGREEMENT





<PAGE>


                          REGISTRATION RIGHTS AGREEMENT

         THIS  REGISTRATION  RIGHTS  AGREEMENT  (the  "Agreement")  is made  and
entered into as of April 8, 1999 by and between KOMAG, INCORPORATED,  a Delaware
corporation ("Komag"),  and WESTERN DIGITAL CORPORATION,  a Delaware corporation
("WDC"). Komag and WDC are referred to collectively herein as the "Parties."


                                    RECITALS

         A. On April 8, 1999,  Komag and WDC  entered  into that  certain  Asset
Purchase  Agreement  ("Purchase  Agreement")  pursuant to which, inter alia, WDC
agreed to sell certain of its assets and properties  utilized in its Santa Clara
Disk Media Operations to Komag (the  "Acquisition") in exchange for, among other
things,  unregistered  shares of Komag's common stock, $0.01 par value per share
("Komag  Common  Stock").  Capitalized  terms used herein not otherwise  defined
herein shall have the meanings set forth in the Purchase Agreement.

         B. As an inducement to the completion of, and as a condition  precedent
to the  completion  of, the  Acquisition,  Komag has  agreed to provide  certain
registration  rights to WDC,  and WDC has agreed to restrict its resale of Komag
Common Stock, in accordance with the terms and conditions of this Agreement.

         NOW,  THEREFORE,  in  consideration  of  the  covenants,  promises  and
agreements set forth herein, and for other good and valuable consideration,  the
receipt and sufficiency is hereby acknowledged, the Parties agree as follows:

         1. Definitions.

                  (a) For purposes of this Agreement,  the following terms shall
have the following respective meanings:

                           (i) "1933 Act" shall mean the Securities Act of 1933,
as amended, or any similar federal statute enacted hereafter,  and the rules and
regulations of the SEC thereunder,  all as the same shall be in effect from time
to time.

                           (ii) "1934 Act"  shall mean the  Securities  Exchange
Act of 1934, as amended,  or any similar federal statute enacted hereafter,  and
the rules and  regulations  of the SEC  thereunder,  all as the same shall be in
effect from time to time.

                           (iii)  "Form S-3" shall mean such form under the 1933
Act as in effect on the date hereof or any registration  form under the 1933 Act
subsequently   adopted  by  the  SEC  which



<PAGE>


similarly  permits  inclusion or  incorporation  of  substantial  information by
reference to other documents filed by Komag with the SEC.

                           (iv) "Initial  Registrable  Amount" shall equal:  (i)
the  number of shares  of Komag  Common  Stock  issued  to WDC  pursuant  to the
Purchase  Agreement  plus (ii) all  securities  which are issued or  received in
respect of, or in exchange or in  substitution  for,  the shares  identified  in
clause (i) hereof  including,  without  limitation,  those  arising from a stock
dividend, distribution, stock split, reclassification,  reorganization,  merger,
consolidation or other exchange of securities.

                           (v) "NASD"  shall mean the  National  Association  of
Securities Dealers, Inc.

                           (vi)  "Person"  shall  mean  an  individual,  a  sole
proprietorship,  a corporation,  a partnership,  a limited liability  company, a
limited liability partnership,  a joint venture, an association,  a trust or any
other entity or organization,  including a government or political  subdivision,
agency or instrumentality thereof.

                           (vii)  The   terms   "register,"   "registered"   and
"registration"  refer to a  registration  effected  by  preparing  and  filing a
registration  statement  ("Registration  Statement") in compliance with the 1933
Act and the  declaration  or  ordering  of  effectiveness  of such  Registration
Statement with the SEC.

                           (viii)  "Registrable  Securities"  shall mean (i) the
shares of Komag Common  Stock  issued to WDC pursuant to the Purchase  Agreement
and (ii)  securities  which are issued or received in respect of, or in exchange
or in substitution  for, the shares  identified in clause (i) hereof  including,
without  limitation,  those arising from a stock dividend,  distribution,  stock
split, reclassification, reorganization, merger, consolidation or other exchange
of securities.  As to any particular Registrable  Securities,  once issued, such
securities  shall cease to be  Registrable  Securities  when (w) a  Registration
Statement  with  respect  to the  sale  of such  securities  shall  have  become
effective  under the Act and such  securities  shall  have been  disposed  of in
accordance with such  Registration  Statement,  (x) such  securities  shall have
ceased to be  outstanding,  (y) such securities  shall have been  transferred as
permitted  by, and in compliance  with,  Rule 144 under the 1933 Act or (z) such
time as all of the  outstanding  Registrable  Securities can be sold by WDC in a
three-month period in accordance with Rule 144 under the 1933 Act.

                           (ix)  "Registration  Period"  shall  mean the  period
commencing on the effective date of a registration  statement  filed pursuant to
Section  3 or 4 hereof  until  such time as all of the  outstanding  Registrable
Securities  can be sold by WDC in a three-month  period in accordance  with Rule
144 under the 1933 Act.

                           (x) "SEC" shall mean the United States Securities and
Exchange Commission.

                                      -2-

<PAGE>


                  (b) The following terms are defined in the following  sections
of this Agreement:


                     Terms                                    Sections
                     -----                                    --------
                     Acquisition                              Preamble
                     Agreement                                Preamble
                     Demand Registration                      4(a)
                     Komag                                    Preamble
                     Komag Common Stock                       Preamble
                     Parties                                  Preamble
                     Piggyback Shares                         2
                     Purchase Agreement                       Preamble
                     Resale Registration Statement            3
                     Unregistered Shares                      3
                     WDC                                      Preamble


         2.  Piggyback  Registration.  If at any time prior to one  hundred  and
eighty (180) days  following the date hereof (the "Initial  Period"),  or at any
time thereafter during the Registration  Period, Komag shall register any shares
of its common  stock for its own account  pursuant to a  Registration  Statement
under the 1933 Act (other than a registration relating to employee benefit plans
or to a  transaction  subject to Rule 145 under the 1933 Act),  Komag  shall use
commercially  reasonable  efforts to cause to be registered on such Registration
Statement and in any underwriting involved therein, subject to and in accordance
with  the  terms,  conditions,  procedures  and  limitations  contained  in this
Agreement,  a number of Registrable  Securities equal to (a) with respect to any
registration  during  the  Initial  Period,  up to thirty  percent  (30%) of the
Registrable  Securities  (the  "Piggyback  Shares") or  (b) with respect  to any
registration  after  the  Initial  Period,  up  to  the  number  of  Registrable
Securities that WDC is entitled to sell pursuant to Section 10(b) below, in each
event as requested to be included by WDC.  Notwithstanding the foregoing,  Komag
shall have the right to delay,  terminate or withdraw any registration initiated
by it under this  Section 2 for any reason  prior to the  effectiveness  of such
registration.

         3. Registration on Resale Registration Statement. If all or any portion
of the Piggyback  Shares are not registered  within one hundred and twenty (120)
days  following  the  date  hereof  (such  unregistered  Piggyback  Shares,  the
"Unregistered  Shares")  and the  Company  does not  provide  WDC with  evidence
reasonably satisfactory to WDC that all such Unregistered Shares will be covered
by an  effective  registration  statement  prior  to the one  hundred  eightieth
(180th)  day  following  the date  hereof,  then  Komag  shall use  commercially
reasonable efforts to prepare and file with the SEC a Registration  Statement on
Form S-3 ("Resale Registration  Statement") covering the Unregistered Shares for
the purpose of registering  such  Unregistered  Shares for resale under the 1933
Act,  which  Resale  Registration  Statement  shall  be  filed  in  a  timeframe
reasonably  expected to result in it being declared effective at the end of such
180-day period.  Such registration shall be underwritten if so requested by WDC.
In addition,  such registration shall be in addition to registration provided in
Section 4 and shall be subject to and in accordance with the terms,  conditions,
procedures and  limitations  contained in this  Agreement.  Notwithstanding  the
foregoing,  Komag shall have the right to delay any registration initiated under
this  Section 3 for a period of not more  than  sixty  (60) days if the Board of
Directors of Komag, acting in good faith,  determines that there exists material
nonpublic  information  which the Board does not wish to  disclose in the Resale
Registration

                                      -3-

<PAGE>


Statement.  If the Board of Directors of Komag makes such  determination,  Komag
shall promptly advise WDC that a delay of such registration is likely.

         4. Demand Registration.

                  (a)  If,  at  any  time,  WDC  is  unable  to  sell  during  a
three-month  period  pursuant  to  Rule  144  under  the  1933  Act,  all of the
Registrable Securities it is permitted to sell pursuant to Section 10(b) hereof,
WDC shall have the right to request,  by written notice,  on one occasion,  that
Komag file a  Registration  Statement  on Form S-3 pursuant to Rule 415 covering
all Registrable  Securities for the purpose of registering such securities under
the 1933 Act ("Demand Registration").  Any such written notice shall (i) specify
the amount of Registrable  Securities  intended to be sold or disposed of by WDC
and (ii) shall state the intended method or methods of disposition (including by
means of an  underwritten  offering) of such  Registrable  Securities.  Promptly
after receiving the written notice of the request for Demand Registration, Komag
shall use commercially  reasonable  efforts to cause all Registrable  Securities
specified in the written  request to be  registered  on the Demand  Registration
Statement  under the 1933 Act,  subject  to and in  accordance  with the  terms,
conditions, procedures and limitations contained in this Agreement.

                  (b)  Notwithstanding   the  foregoing,   Komag  shall  not  be
obligated to effect the filing of a  registration  pursuant to Section 4(a): (i)
at any time prior to  September  8,  2000,  (ii) after  Komag has  effected  one
registration  pursuant to Section  4(a), or (iii) if, at the time of any request
to register Registrable Securities pursuant to Section 4(a), Komag is preparing,
or within ten (10) days thereafter engages an underwriter, and commences in good
faith to prepare,  a Registration  Statement for a public offering (other than a
registration  relating solely to employee  benefit plans) which is in fact filed
and becomes  effective  within  ninety (90) days after the date WDC has provided
the written request, or is engaged in any material acquisition or divestiture or
other  business  transaction  with a third party which the Board of Directors of
Komag  reasonably  determines  in good faith would be adversely  affected by the
Demand  Registration to the material  detriment of Komag,  then Komag may at its
option  direct  that such  Demand  Registration  be delayed  for a period not in
excess of ninety (90) days from the date of such request.

         5.  Demand  Obligations  of Komag.  Whenever  Komag is  required  under
Section 3 or 4 of this Agreement to effect the  registration  of any Registrable
Securities:

                  (a)  Komag   shall  (i)  prepare  and  file  with  the  SEC  a
Registration  Statement covering the Registrable Securities and use commercially
reasonable efforts to cause such Registration Statement to be declared effective
by the SEC and to keep such registration  effective until the termination of the
Registration  Period;  (ii)  prepare and file with the SEC such  amendments  and
supplements to such Registration Statement and the prospectus used in connection
therewith as may be necessary and to comply with the  provisions of the 1933 Act
with  respect to the sale or other  disposition  of all  Registrable  Securities
proposed to be registered in such  Registration  Statement until  termination of
the  Registration  Period;  (iii)  furnish  to WDC such  number of copies of any
prospectus (including any preliminary prospectus and any amended or supplemented
prospectus) in conformity with the  requirements of the 1933 Act, and such other
documents  as WDC may  reasonably  request,  in order to effect the offering and
sale of the Registrable  Securities to be offered and sold, but only while Komag
shall be required under the provisions hereof to cause the

                                      -4-

<PAGE>


Registration  Statement to remain current; and (iv) use commercially  reasonable
efforts  to  register  or qualify  the  Registrable  Securities  covered by such
Registration   Statement   under  the  securities  or  blue  sky  laws  of  such
jurisdictions as WDC shall reasonably request;  provided that Komag shall not be
required in  connection  therewith  or as a  condition  thereto to qualify to do
business  or to file a  general  consent  to  service  of  process  in any  such
jurisdiction where it has not been qualified.

                  (b)  Komag  shall  notify  WDC (i)  when a  prospectus  or any
prospectus  supplement or  post-effective  amendment  has been filed,  and, with
respect to such Registration Statement or any post-effective amendment, when the
same has become  effective;  (ii) of any request by the SEC or any other federal
or state  governmental  authority  during  the period of  effectiveness  of such
Registration  Statement  for  amendments  or  supplements  to such  Registration
Statement or related  prospectus or for additional  information  relating to the
Registration Statement; (iii) of the issuance by the SEC or any other federal or
state  governmental  authority of any stop order suspending the effectiveness of
the  Registration  Statement  or the  initiation  of any  proceedings  for  that
purpose;  (iv) of  Komag's  receipt  of any  notification  with  respect  to the
suspension of the  qualification  or exemption from  qualification of any of the
Registrable  Securities  for  sale  in any  jurisdiction  or the  initiation  or
threatening of any  proceeding for such purpose;  or (v) of the happening of any
event which makes any statement made in such  Registration  Statement or related
prospectus or any document  incorporated or deemed to be incorporated therein by
reference  untrue in any  material  respect or which  requires the making of any
changes in such  Registration  Statement or  prospectus  so that, in the case of
such  Registration  Statement,  it will not  contain any untrue  statement  of a
material fact or omit to state any material  fact required to be stated  therein
or necessary to make the statements therein not misleading, and that in the case
of the prospectus,  it will not contain any untrue  statement of a material fact
or omit to state any material fact necessary to make the statements  therein, in
the light of the circumstances under which they were made, not misleading.  Upon
the  happening of any event (A) of the kind  described in clauses  (ii),  (iii),
(iv), or (v) hereof or, (B) that, in the good faith judgment of Komag's Board of
Directors,  renders it advisable to suspend use of the prospectus due to pending
corporate developments, public filings with the SEC or similar events, Komag may
suspend use of the  prospectus on notice to WDC;  provided,  however,  that with
respect to the events described in clauses (A)(v) or (B) of this sentence, Komag
shall use commercially reasonable efforts to take such steps as are necessary to
permit the  continued  use of the  prospectus  as soon as  possible  and, in any
event, no such  suspension  shall be longer than 90 days in any one year period.
Upon such suspension of the  prospectus,  WDC shall  discontinue  disposition of
Registrable  Securities  covered by such  Registration  Statement or  prospectus
until copies of a supplemented  or amended  prospectus are distributed to WDC or
until  WDC is  advised  in  writing  by  Komag  that  the use of the  applicable
prospectus  may be resumed  and, if so  directed,  WDC will deliver to Komag (at
Komag's  expense)  all copies,  other than  permanent  file copies then in WDC's
possession,  of the prospectus covering such Registrable  Securities at the time
of receipt of such notice.  Komag shall use commercially  reasonable  efforts to
obtain  the  withdrawal  of any  order  suspending  the  effectiveness  of  such
Registration  Statement,  or the lifting of any suspension of the  qualification
(or exemption from qualification) of any of the Registrable  Securities for sale
in any  jurisdiction,  at the  earliest  practicable  time.  Except as expressly
provided in this Section 5(b), during the Registration Period, Komag shall fully
comply  with the  rules  and  regulations  promulgated  under  the 1933 Act with
respect to shelf  Registration  Statements  pursuant to Rule 415 of the 1933 Act
and upon the occurrence of any event  contemplated by clause (v),  promptly (and
in no event more than fifteen  (15) days after such event)  prepare a supplement
or post-effective amendment to such Registration

                                      -5-

<PAGE>


Statement or a supplement to the related prospectus or any document incorporated
therein by reference or file any other required  document so that, as thereafter
delivered to the purchasers of the Registrable Securities being sold thereunder,
such prospectus will not contain an untrue  statement of a material fact or omit
to state a material fact necessary to make the statements  therein,  in light of
the circumstances under which they were made, not misleading.

         6. Additional  Obligations of Komag. In connection with any offering of
Registrable  Securities  registered pursuant to this Agreement,  Komag shall (i)
furnish  WDC, at Komag's  expense,  with  unlegended  certificates  representing
ownership of the Registrable  Securities being sold in such denominations as WDC
shall request, (ii) instruct the transfer agent and registrar of the Registrable
Securities to release any stop transfer  orders with respect to the  Registrable
Securities being sold and (iii) use commercially reasonable efforts to cause all
Registrable  Securities included in such Registration Statement to be listed, by
the  date  of  the  first  sale  of  Registrable  Securities  pursuant  to  such
Registration  Statement,  on each  securities  exchange on which shares of Komag
Common Stock are then listed or proposed by Komag to be listed.

         7.  Furnish  Information.   In  connection  with  any  registration  of
Registrable  Securities  pursuant to this Agreement,  WDC shall provide all such
information and materials to Komag regarding it, the Registrable Securities held
by it  and  the  intended  method  of  disposition  by it  of  such  Registrable
Securities and shall take all such action as may be reasonably required in order
to permit Komag and any underwriters to comply with all applicable  requirements
of the SEC and the NASD and to obtain any desired  acceleration of the effective
date of the Registration  Statement covering such Registrable  Securities.  Such
provision  of  information  and  materials  is  a  condition  precedent  to  the
obligations  of Komag  pursuant  to this  Agreement.  Komag  shall only use in a
Registration   Statement  or  prospectus  information  regarding  WDC  expressly
designated by WDC for use in such Registration Statement or prospectus.

         8. Underwriting Requirements; Underwriting Priorities.

                  (a) With respect to any registration  effectuated  pursuant to
Section 3 of this Agreement,  Komag will have the right to select the investment
banker(s) and manager(s), if any, to administer any such offerings of securities
subject to the reasonable  consent of WDC; and, with respect to any registration
effectuated pursuant to Section 4 of this Agreement, WDC shall have the right to
select the investment  banker(s) and manager(s),  if any, to administer any such
offering of securities, subject to the reasonable consent of Komag.

                  (b)  If  any  registration  pursuant  to  Section  2 is  for a
registered public offering involving an underwriting,  Komag shall so advise. In
such event the rights of WDC to registration pursuant to this Agreement shall be
conditioned upon WDC's  participation in such  underwriting and the inclusion of
WDC's Registrable  Securities in the underwriting to the extent provided herein.
WDC shall  (together with Komag and any other  stockholders  distributing  their
securities through such  underwriting) (i) enter into an underwriting  agreement
in  customary  form  with the  underwriter  or  underwriters  selected  for such
underwriting  by Komag and (ii)  complete and execute all other  questionnaires,
powers of attorney,  indemnities and other documents  reasonably  required under
the terms of such underwriting agreement. If WDC disapproves of the terms of any
such underwriting,  WDC may elect to withdraw therefrom by written notice to WDC
and the underwriter.

                                      -6-

<PAGE>


                  (c)  Notwithstanding  any other  provision  contained  in this
Agreement to the contrary,  with respect to any registration pursuant to Section
2  hereof,  if the  underwriter  determines  that  marketing  factors  require a
limitation of the number of securities to be  underwritten,  the underwriter may
limit or exclude  the amount of  Registrable  Securities  to be  included in the
registration   and   underwriting  as  follows:   Komag  will  include  in  such
registration  (i) first,  all of the securities  Komag proposes to sell and (ii)
second, subject to the obligations of Komag pursuant to contractual registration
rights  granted by Komag  prior to the date of this  Agreement,  the  securities
sought to be registered by WDC and the  beneficial  owners  thereof,  other than
WDC,  on a prorata  basis  based upon the number of shares of Komag owned by WDC
and such persons. In the event of any such limitation or inclusion of fewer than
all of the Registrable Securities, Komag shall so advise.

         9. Expenses. Komag shall pay all of the out-of-pocket expenses incurred
in connection with the registration of Registrable  Securities  pursuant to this
Agreement,  including all SEC, NASD and blue sky  registration  and filing fees,
printing  expenses,  transfer  agents' and  registrars'  fees,  and the fees and
disbursements of Komag's outside counsel and independent  accountants;  provided
that,  if  any  registration   pursuant  to  Section  4  of  this  Agreement  is
underwritten at the request of WDC, all such expenses that would not be incurred
but for the fact that such registration is underwritten  shall be the obligation
of WDC. Without limiting the foregoing, WDC shall pay all underwriting discounts
and commissions and applicable  transfer taxes as well as all  disbursements  of
any legal counsel retained by it.

         10. Lockup Agreement.

                  (a) Except as provided in  subsection  (b) of this Section 10,
WDC agrees not to offer to sell, contract to sell or otherwise sell, dispose of,
loan, pledge or grant any rights with respect to (collectively, a "Disposition")
any  Registrable  Securities  for a period of  beginning on the Closing Date and
expiring  on the  forty-two  (42) month  anniversary  of the  Closing  Date (the
"Restricted Period"),  otherwise than (i) as a bona fide gift or gifts, provided
the  donee or  donees  thereof  agree to be bound by this  Agreement,  (ii) as a
distribution to stockholders of WDC, provided the distributees  thereof agree in
writing to be bound by the terms of this Agreement,  (iii) as a bona fide pledge
of the  Registrable  Securities  by WDC to BankBoston or any of its other senior
lenders,  or (iv)  with  the  prior  written  consent  of  Komag.  The  forgoing
restriction  is  expressly  agreed to  preclude  the  holder of the  Registrable
Securities from engaging in any hedging or other  transaction  which is designed
to or reasonably  expected to lead to or result in a Disposition  of Registrable
Securities  during the  Restricted  Period even if such  Registrable  Securities
would be disposed of by someone other than WDC. Such prohibited hedging or other
transactions would include,  without limitation,  any short sale (whether or not
against the box) or any purchase, sale or grant of any right (including, without
limitation,  any put or call option) with respect to any Registrable  Securities
or with  respect to any  security  (other than a  broad-based  market  basket or
index) that includes,  relates to or derives any  significant  part of its value
from Registrable Securities.  Furthermore,  WDC agrees and consents to the entry
of stop transfer  instructions  with Komag's transfer agent against the transfer
of Registrable Securities except in compliance with this Agreement.

                                      -7-

<PAGE>


                  (b) WDC may  engage  in one or more  Dispositions  (including,
without  limitation,  engaging  in  hedging  transactions)  of  the  Registrable
Securities pursuant to the schedule set forth below:

                           (i) From the Closing  Date until  April 8, 2000,  WDC
may engage in Dispositions of Registrable  Securities which have been registered
for resale pursuant to Sections 2 and 3 hereof.

                           (ii) On and after April 8, 2000 (12 months  after the
Closing Date), WDC may engage in one or more Dispositions  that, when aggregated
with all prior sales of Registrable Securities, equals up to forty-five (45%) of
the Initial Registrable Amount;

                           (iii) On and after  October 8, 2000 (18 months  after
the  Closing  Date),  WDC may  engage  in one or more  Dispositions  that,  when
aggregated  with all prior sales of Registrable  Securities,  equals up to sixty
percent (60%) of the Initial Registrable Amount;

                           (iv) On and after  October 8, 2001 (30  months  after
the  Closing  Date),  WDC may  engage  in one or more  Dispositions  that,  when
aggregated with all prior sales of Registrable  Securities,  equals up to ninety
percent (90%) of the Initial Registrable Amount;

                           (v)  After  October  8,  2002 (42  months  after  the
Closing  Date),  WDC  may  engage  in one  or  more  Dispositions  of all of the
Registrable Securities.

         11.  Assignment  of  Registration   Rights.  The  rights,   duties  and
obligations of Komag and WDC pursuant to this Agreement may not be assigned,  by
operation of law or otherwise, except to a direct or indirect subsidiary of WDC.

         12.  Indemnification  and  Contribution.  In the event of any  offering
registered pursuant to this Agreement:

                  (a)  Komag  will  indemnify  and hold  harmless  WDC and WDC's
officers and directors,  and each underwriter,  if any, of securities being sold
by WDC,  against any losses,  claims,  damages or  liabilities  to which WDC may
become  subject under the 1933 Act and the 1934 Act arising out of or based upon
(i) any untrue  statement  or alleged  untrue  statement  of any  material  fact
contained in any registration statement, or any amendment or supplement thereto,
incident to any offering registered pursuant to this Agreement,  or the omission
or alleged  omission  to state  therein a material  fact  necessary  to make the
statements  therein  not  misleading,  or (ii) any untrue  statement  or alleged
untrue  statement  of any material  fact  contained  in any  prospectus,  or any
amendment or supplement thereto, incident to any offering registered pursuant to
this Agreement,  or the omission or alleged omission to state therein a material
fact necessary to make the statements therein, in the light of the circumstances
under which they were made, not misleading,  and agrees to reimburse WDC for any
legal  or  other  expenses   reasonably   incurred  by  it  in  connection  with
investigating or defending any such loss,  claim,  damage,  liability or action;
provided, however, that Komag shall not be liable in any such case to the extent
that any such loss, claim, damage, liability or action arises out of or is based
upon an untrue  statement  or alleged  untrue  statement  or omission or alleged
omission  made in such  registration  statement,  such  prospectus,  or any such
amendment or supplement  thereto,

                                      -8-

<PAGE>


in reliance upon, and in conformity with,  information relating to WDC furnished
by WDC or its agents or representatives to Komag or any underwriter specifically
for use in the preparation  thereof and,  provided  further,  that the indemnity
agreement  provided in this Section  12(a) shall not inure to the benefit of WDC
where the person asserting any losses, claims,  damages,  liabilities or actions
arising from any untrue  statement or alleged untrue  statement of material fact
or omission or alleged  omission to state  therein a material fact had purchased
Komag  securities  from WDC and WDC had failed to deliver to such  person in the
manner and within the time  required by the 1933 Act a copy of a  prospectus  in
which such untrue  statement or alleged untrue  statement or omission or alleged
omission was corrected,  unless such failure is the result of  noncompliance  by
Komag with Section 5(a)(iii) hereof.

         The  indemnity  agreement in this  Section  12(a) shall extend upon the
same terms and conditions to, and shall inure to the benefit of, each person, if
any, who controls WDC and each  underwriter,  if any,  within the meaning of the
1933 Act or the 1934 Act.

                  (b)  WDC  will,  if  Registrable  Securities  held  by WDC are
included  in the  securities  to which  such  registration  is  being  effected,
indemnify and hold harmless Komag and Komag's  officers and directors,  and each
underwriter,  if any,  of  securities  covered by such  Registration  Statement,
against  any losses,  claims,  damages or  liabilities  to which such Person may
become  subject under the 1933 Act and the 1934 Act arising out of or based upon
(i) any untrue  statement  or alleged  untrue  statement  of any  material  fact
contained in any registration  statement or any amendment or supplement thereto,
incident to any offering registered pursuant to this Agreement,  or the omission
or alleged  omission  to state  therein a material  fact  necessary  to make the
statements  therein  not  misleading,  or (ii) any untrue  statement  or alleged
untrue  statement  of any  material  fact  contained  in any  prospectus  or any
amendment or supplement thereto, incident to any offering registered pursuant to
this Agreement,  or the omission or alleged omission to state therein a material
fact necessary to make the statements therein, in the light of the circumstances
under  which they were made,  not  misleading,  to the extent  that such  untrue
statement or alleged untrue  statement or omission or alleged  omission was made
in reliance upon and in conformity with written  information  furnished to Komag
or  any  underwriter  by  WDC,   directly  or  through  WDC's   representatives,
specifically for use in the preparation  thereof, and agrees to reimburse Komag,
Komag's  officers and directors and each  underwriter,  if any, for any legal or
other  expenses   reasonably   incurred  by  such  Person  in  connection   with
investigating or defending any such loss,  claim,  damage,  liability or action;
provided, that the liability of WDC under this Section 12(a) shall be limited to
an amount equal to the gross proceeds before  expenses and commissions  from all
sales of securities by WDC under any  registration  statement  filed pursuant to
this Agreement.

         The  indemnity  agreement in this  Section  12(b) shall extend upon the
same terms and conditions to, and shall inure to the benefit of, each Person, if
any, who controls Komag and each underwriter,  if any, within the meaning of the
1933 Act or the 1934 Act.

                  (c) Each party entitled to indemnification  under this Section
12 (the "Indemnified  Party") shall give notice to the party required to provide
indemnification (the "Indemnifying Party") promptly after such Indemnified Party
receives  written notice of any claim as to which  indemnity may be sought,  and
shall permit the  Indemnifying  Party to assume the defense of any such claim or
any litigation resulting  therefrom,  provided that counsel for the Indemnifying
Party,  who shall

                                      -9-

<PAGE>


conduct  the  defense  of such claim or  litigation,  shall be  approved  by the
Indemnified Party (whose approval shall not be unreasonably  withheld),  and the
Indemnified  Party may  participate  in such  defense  at such  party's  expense
(unless the Indemnified  Party  reasonably and in good faith  determines,  after
consultation  with independent  counsel,  that there are additional  defenses or
claims  that it may assert  that are  adverse to or not in the  interest  of the
Indemnifying Party and separate counsel is required to represent such interests,
in which case the  reasonable  expenses of such counsel shall be paid for by the
Indemnifying  Party),  and provided  further that the failure of any Indemnified
Party to give notice as provided herein shall not relieve the Indemnifying Party
of its  obligations  under  this  Agreement,  except  to  the  extent  that  the
Indemnifying  Party's  ability to defend  against  such claim or  litigation  is
impaired  as a  result  of such  failure  to give  notice.  Notwithstanding  the
foregoing sentence,  the Indemnified Party may retain its own counsel to conduct
the  defense  of any such  claim or  litigation,  and  shall be  entitled  to be
reimbursed by the  Indemnifying  Party for expenses  incurred by the Indemnified
Party in defense of such claim or litigation, in the event that the Indemnifying
Party does not assume the defense of such claim or litigation  within sixty days
after  the   Indemnifying   Party  receives  written  notice  thereof  from  the
Indemnified  Party.  Further,  an Indemnifying Party shall be liable for amounts
paid in  settlement  of any such claim or  litigation  only if the  Indemnifying
Party  consents  in  writing  to such  settlement  (which  consent  shall not be
unreasonably  withheld). No Indemnifying Party, in the defense of any such claim
or litigation,  shall,  except with the consent of each Indemnified Party (which
consent shall not be unreasonably withheld), consent to entry of any judgment or
enter any  settlement  which does not include an  unconditional  release of each
such  Indemnified  Party  from  all  liability  in  respect  to  such  claim  or
litigation.

                  (d) The  obligations  of Komag and WDC under  this  Section 12
shall survive the  completion  of any offering of  securities in a  registration
statement under this Agreement or otherwise.

         13.  Amendments.  No amendment of any provision of this Agreement shall
be valid  unless  the same  shall be in  writing  and  signed  by Komag  and the
Company. No waiver by any Party of any default, misrepresentation,  or breach of
warranty or covenant  hereunder,  whether intentional or not, shall be deemed to
extend  to any  prior or  subsequent  default,  misrepresentation,  or breach of
warranty or covenant hereunder or affect in any way any rights arising by virtue
of any prior or subsequent such occurrence.

         14. Rule 144 Reporting. With a view to making available the benefits of
certain rules and  regulations  of the SEC which may at any time permit the sale
of the  Registrable  Securities to the public without  registration,  after such
time as a public market exists for the securities of Komag, Komag agrees to:

                  (a) Make and keep public information available, as those terms
are  understood  and  defined in Rule 144 under the 1933 Act, at all times after
the date hereof;

                  (b) Use commercially  reasonable  efforts to file with the SEC
in a timely manner all reports and other  documents  required of Komag under the
1933 Act and the 1934 Act; and

                                      -10-

<PAGE>


                  (c) So long as WDC owns any Registrable Securities, furnish to
WDC  forthwith  upon request a written  statement by Komag as to its  compliance
with the  reporting  requirements  of Rule 144, and of the 1933 Act and the 1934
Act,  a copy of the most  recent  annual or  quarterly  report of Komag and such
other reports and documents of Komag as WDC may  reasonably  request in availing
itself  of any  rule or  regulation  of the SEC  allowing  WDC to sell  any such
securities without registration.

         15.  Termination.  The registration  rights set forth in this Agreement
shall  terminate  (and  the  shares  held  by  WDC  shall  cease  to  constitute
Registrable Securities) (a) at any time, upon mutual agreement in writing of the
Parties hereto or (b) upon such time as all of the  Registrable  Securities then
held by WDC can be sold by WDC in a three-month  period in accordance  with Rule
144 under the 1933 Act.

         16. Notice. All notices and other communications  required or permitted
under  this  Agreement  shall be deemed  to have been duly  given and made if in
writing  and if  served  either  by  personal  delivery  or by  facsimile  (with
telephonic  confirmation of receipt) to the party for whom intended (which shall
include delivery by Federal Express or similar nationally recognized service) or
three  business  days after  being  deposited,  postage  prepaid,  certified  or
registered mail, return receipt requested, in the United States mail bearing the
address shown in this  Agreement for, or such other address as may be designated
in writing hereafter by, such party:

If to WDC:                          Western Digital Corporation
                                    8105 Irvine Center Drive
                                    Irvine, CA  92618
                                    Attn:  General Counsel
                                    Telephone:  (949) 932-5133
                                    Facsimile:   (949) 932-7837

with a copy to:                     Gibson, Dunn & Crutcher LLP
                                    1530 Page Mill Road
                                    Palo Alto, CA  94304
                                    Attn: Gregory T. Davidson, Esq.
                                    Telephone:  (650) 849-5300
                                    Facsimile:   (650) 849-5333

If to Komag:                        Komag, Incorporated
                                    1704 Automation Parkway
                                    San Jose, CA  95131
                                    Attn:  Chief Financial Officer
                                    Telephone:  (408) 576-2000
                                    Facsimile:  (408) 944-9255

                                      -11-

<PAGE>


with a copy to:                     Wilson Sonsini Goodrich & Rosati
                                    650 Page Mill Road
                                    Palo Alto, CA  94304
                                    Attn:  Steven V. Bernard
                                    Telephone:  (650) 493-9300
                                    Facsimile:   (650) 493-6811

         Any party may change the address to which notices,  requests,  demands,
claims and other  communications  hereunder  are to be  delivered  by giving the
other  party  notice in the  manner  herein  set  forth.

         17.  Counterparts  and  Facsimile  Signatures.  This  Agreement  may be
executed, including by facsimile signature, in one or more counterparts, each of
which  when so  executed  shall be  deemed  to be an  original  and all of which
together shall constitute one and the same instrument.

         18.  Interpretation.  Unless the  context of this  Agreement  otherwise
requires,  (i) words of any gender  include  each gender and neuter,  (ii) words
using the singular or plural number also include the plural or singular  number,
respectively,  (iii) the terms  "hereof,"  "herein,"  "hereby" and derivative or
similar  words  refer to this  entire  Agreement,  (iv) the terms  "Article"  or
"Section" refer to the specified  Article or Section of this Agreement;  (v) the
term  "including" or similar words shall be construed as to refer to such matter
without limitation thereof.  Whenever this Agreement refers to a number of days,
such number shall refer to calendar days unless business days are specified. The
headings  contained in this Agreement are for reference  purposes only and shall
not affect in any way the meaning or interpretation of this Agreement.

         19. Severability.  In the event that any provision of this Agreement or
the  application  thereof,  becomes  or is  declared  by a  court  of  competent
jurisdiction  to be  illegal,  void  or  unenforceable,  the  remainder  of this
Agreement  will  continue in full force and effect and the  application  of such
provision to other persons or circumstances will be interpreted so as reasonably
to effect the intent of the parties hereto. The parties further agree to replace
such  void or  unenforceable  provision  of  this  Agreement  with a  valid  and
enforceable  provision that will achieve, to the extent possible,  the economic,
business and other purposes of such void or unenforceable provision.

         20.  Governing Law. This Agreement  shall be governed by, and construed
and enforced in accordance with, the internal laws of the State of Delaware.

         21. Entire Agreement.  This Agreement (including the documents referred
to herein)  constitutes the entire agreement between the Parties with respect to
the subject matter hereof and supersedes any prior  understandings,  agreements,
or  representations  by or between the Parties,  written or oral,  to the extent
they related in any way to the subject matter hereof.


                  [Remainder of Page Intentionally Left Blank]


                                      -12-

<PAGE>


         IN WITNESS WHEREOF,  the Parties hereto have executed this Agreement as
of the date first above written.



                                              KOMAG, INCORPORATED

                                              By: ______________________________
                                                  Name:
                                                  Title:


                                              WESTERN DIGITAL CORPORATION

                                              By: ______________________________
                                                  Name:
                                                  Title:



                 [Registration Rights Agreement Signature Pages]



                                      -13-




                                                                     Exhibit 5.1


                [Letterhead of Wilson Sonsini Goodrich & Rosati]


                                December 17, 1999


Komag, Incorporated
1704 Automation Parkway
San Jose, CA 95131

                  Re: Registration Statement on Form S-3

Ladies and Gentlemen:

         We have examined the Registration  Statement on Form S-3 to be filed by
you with the  Securities  and Exchange  Commission on or about December 17, 1999
(the  "Registration  Statement"),  in connection with the registration under the
Securities  Act of 1933,  as amended,  of up to 3,234,940  shares of your Common
Stock (the  "Shares").  As your legal counsel,  we have examined the proceedings
taken by you in connection with the issuance and sale of the Shares.

         It is our  opinion  that the Shares  have been  legally  issued and are
fully paid and non-assessable.

         We consent to the use of this opinion as an exhibit to the Registration
Statement and further  consent to the use of our name wherever  appearing in the
Registration  Statement,  including the Prospectus  constituting a part thereof,
and any amendments thereto.



                                         Very truly yours,

                                         WILSON SONSINI GOODRICH & ROSATI
                                         Professional Corporation

                                         /s/ Wilson Sonsini Goodrich & Rosati

                                      II-2




                                                                    Exhibit 23.1


               Consent of Ernst & Young LLP, Independent Auditors

         We consent to the reference to our firm under the caption  "Experts" in
the  Registration   Statement  (Form  S-3)  and  related  Prospectus  of  Komag,
Incorporated for the registration of 3,234,940 shares of its Common Stock and to
the  incorporation  by reference  therein of our report dated  January 22, 1999,
with respect to the  consolidated  financial  statements  and schedule of Komag,
Incorporated  included  in its  Annual  Report  (Form  10-K) for the year  ended
January 3, 1999.


                                               /s/ Ernst & Young LLP



San Jose, California

December 16, 1999


                                       II-3




                                                                    Exhibit 23.3


                       Consent of Independent Accountants


         We  consent  to the  incorporation  by  reference  in the  registration
statement of Komag,  Incorporated  on Form S-3 of our report  dated  January 22,
1999 on our audits of the consolidated  financial statements of Asahi Komag Co.,
Ltd.  and its  subsidiary  as of December  31, 1998 and 1997,  and for the years
ended December 31, 1998,  1997 and 1996,  which report is included in the Annual
Report on Form 10-K of Komag, Incorporated for the year ended January 3, 1999.


                                        /s/ Chuo Audit Corporation

Tokyo, Japan

December 16, 1999

                                      II-4



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