<PAGE> 1
PROSPECTUS SUPPLEMENT DATED OCTOBER 1, 1997
(To Prospectus dated June 24, 1997)
ADAPTEC, INC.
U.S. $230,000,000
4 3/4% Convertible Subordinated Notes due February 1, 2004
and
Shares of Common Stock Issuable Upon Conversion Thereof
-----------------------
This Prospectus Supplement together, with the Prospectus, is to be used
by certain holders of the above-referenced securities or by their transferees,
pledgees, donees or their successors in connection with the offer and sale of
the above referenced securities.
<PAGE> 2
The table captioned "Selling Securityholders" commencing on page 52 of
the Prospectus is hereby amended to reflect the following additions and changes.
<TABLE>
<CAPTION>
NUMBER OF SHARES OF
PRINCIPAL AMOUNT OF NOTES COMMON-STOCK-BENEFICIAL
BENEFICIALLY-OWNED OWNED AND OFFERED
SELLING SECURITYHOLDER AND OFFERED HEREBY HEREBY(1)(2)
- ------------------------------------------------------ ------------------------- -----------------------
<S> <C> <C>
General Motors Investment Management Corp. (3)........ 7,000,000 135,501
NatWest Securities Corporation........................ 5,000,000 96,786
Bear Stearns & Co. (4) (5)............................ 747,000 14,459
Robertson Stephens & Co. L.L.P (4)(5)................. 500,000 9,678
Market Main & Co...................................... 100,000 1,935
</TABLE>
(1) Includes shares of Common Stock issuable upon conversion of the Notes.
(2) Assumes a conversion price of $51.66 per share, and a cash payment in lieu
of any fractional share interest; such conversion price is subject to
adjustment as described under "Description of Notes -- Conversion."
Accordingly the number of shares of Common Stock issuable upon conversion
of the Notes may increase or decrease from time to time. Under the terms of
Indenture, fractional shares will not be issued upon conversion of the
Notes; cash will be paid in lieu of fractional shares, if any.
(3) Represents shares beneficially owned by various employee benefit plans of
General Motors Corporation. The Selling Shareholder has agreed to sell
$1,000,000 in aggregate principal amount of the Notes offered hereby to
Goldman Sachs and Co.
(4) Within the past three years, Bear Stearns & Co. and Robertson Stephens &
Co., L.L.P. have acted as an underwriter of securities of the Company.
(5) Represents additional Notes and Shares being registered by the Selling
Shareholder.
-2-
