<PAGE>
Prospectus Supplement filed under Rule 424(b)(3)
in connection with Registration Statement No. 333-48047
PROSPECTUS SUPPLEMENT NO. 1 DATED JULY 13, 1998
(To Prospectus Dated May 28, 1998)
PLATINUM technology, inc.
$150,000,000 6.25% Convertible Subordinated Notes Due 2002
and Shares of Common Stock Issuable Upon Conversion Thereof
This Prospectus Supplement supplements information contained in that
certain Prospectus, dated May 28, 1998 (the "Prospectus"), relating to the offer
and sale by certain Selling Securityholders of up to $150,000,000 6.25%
Convertible Subordinated Notes Due 2002 and shares of Common Stock issuable upon
conversion thereof (the "Securities") of PLATINUM technology, inc. (the
"Company"). This Prospectus Supplement is not complete without, and may not be
delivered or utilized except in connection with, the Prospectus, including any
amendments or supplements thereto. Capitalized terms used herein but not defined
have the meanings assigned to such terms in the Prospectus. The following table
amends and supplements the information set forth in the Prospectus under the
caption "Selling Securityholders," and, with respect to "Any other holders of
Notes", the information below supersedes the information contained in the
Prospectus for "Any other holders of Notes or future transferees, pledgees,
donees or successors of any such other holder" in the table under the caption
"Selling Securityholders."
<TABLE>
<CAPTION>
Principal Amount of
Securities Beneficially Owned
------------------------------------------
Number of
Number of Principal Shares of
Principal Shares of Amount of Common Stock
Amount of Common Notes That That May
Name Notes Percentage Stock(1)(2) May Be Sold Be Sold
- -------------------------------- ----------- ---------- ----------- ------------ -----------
<S> <C> <C> <C> <C> <C>
Banc America Robertson Stephens $ 4,000,000 2.7% 110,949 $ 4,000,000 110,949
Donaldson Lufkin & Jenrette
Securities Corp. (3) 100,000 * 2,773 100,000 2,773
SBC Warburg Dillon Read Inc. 1,000,000 * 27,737 1,000,000 27,737
Any other holders of Notes (4)(5) 29,425,000 19.6 816,170 29,425,000 816,170
==================================================================================================================================
</TABLE>
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* Less than 1%.
(1) Assumes conversion of the full amount of Notes held by such holder at the
initial rate of $36.0525 in principal amount of Notes per share of Common
Stock; such conversion price is subject to adjustment as described in the
Prospectus under "Description of Notes - Conversion." Under the terms of
the Indenture, fractional shares will not be issued upon conversion of the
Notes; cash will be paid in lieu of any fractional shares.
(2) The number of conversion shares beneficially owned by each Selling
Securityholder named herein is less than 1% of the Company's outstanding
Common Stock as of July 13, 1998.
(3) From time to time, Donaldson, Lufkin & Jenrette Securities Corporation or
their affiliates have provided, and may continue to provide, investment
banking and financial advisory services to the Company, for which they have
received or will receive customary fees.
(4) Information concerning other Selling Securityholders will be set forth in
supplements to this Prospectus from time to time, if required.
(5) Assumes that "Any other holders of Notes" do not beneficially own any Common
Stock other than the Common Stock issuable upon conversion of the Notes at
the initial conversion price.
This Prospectus Supplement is dated July 13, 1998
