Prospectus Supplement #4	Filed pursuant to Rule 424(b)(3)
(to prospectus dated January 17, 2003)	Registration No. 333-89666

ADAPTEC, INC.

3% Convertible Subordinated Notes Due 2007 and

Shares of Common Stock Issuable Upon Conversion of the Notes

This prospectus supplement relates to the resale by the holders of our 3% convertible subordinated notes due 2007 and the shares of our common stock issuable upon the conversion of the notes. You should read this prospectus supplement in conjunction with the prospectus dated January 17, 2003, which is to be delivered with this prospectus supplement.

The information in the table appearing under the heading “Selling Securityholders” in the prospectus is amended by the addition of the information appearing in the table below with respect to persons not previously listed in the prospectus:

Principal Amount of Notes

Number of Shares of Common Stock

Selling Securityholder (1)

Beneficially Owned

and Offered

Hereby (1)

Percentage of

Notes

Outstanding

Beneficially

Owned (1)(2)

Offered

Hereby

Owned After

the Offering

BNP Paribas Arbitrage (†)(36)

5,000,000

2.00%

326,541

(†) Each of these selling securityholders is also an affiliate of a broker-dealer. Each of these selling securityholders has indicated to us that they have purchased the notes in the ordinary course of business, and at the time of such purchase, had no agreements or understandings, directly or indirectly, with any person to distribute the notes or the shares of common stock issuable upon conversion of the notes.

(1) Information regarding the selling securityholders may change from time to time. Any such changed information will be set forth in prospectus supplements if and when necessary. Amounts indicated may be in excess of the total amount registered due to sales or transfers exempt from the registration requirements of the Securities Act since the date upon which the selling securityholders provided information to us regarding their notes.

(2) Assumes a conversion price of approximately $15.31 per share and a cash payment in lieu of any fractional share interest. However, this conversion price will be subject to adjustment as described under “Description of Notes—Conversion Rights.” As a result, the amount of common stock issuable upon conversion of the notes may increase or decrease in the future.

(36) Mike Cohen, Director of Trading, has investment control over these securities.

Investing in our common stock or the notes involves a high degree of risk. Please carefully consider the “Risk Factors” beginning on page 7 of the prospectus, as well as the “Risk Factors” sections included in our recent reports filed with the Securities and Exchange Commission, including our Quarterly Report on Form 10-Q for the quarter ended December 31, 2002.

NEITHER THE SECURITIES AND EXCHANGE COMMISSION NOR ANY STATE SECURITIES COMMISSION HAS APPROVED OR DISAPPROVED OF THESE SECURITIES OR PASSED UPON THE ADEQUACY OR ACCURACY OF THE PROSPECTUS OR THIS PROSPECTUS SUPPLEMENT. ANY REPRESENTATION TO THE CONTRARY IS A CRIMINAL OFFENSE.

The date of this prospectus supplement is June 6, 2003.