QuickLinks -- Click here to rapidly navigate through this document

Exhibit 99.1

CERTIFICATION OF CHIEF EXECUTIVE OFFICER AND CHIEF FINANCIAL OFFICER
PURSUANT TO
18 U.S.C. SECTION 1350,
AS ADOPTED PURSUANT TO
SECTION 906 OF THE SARBANES-OXLEY ACT OF 2002

        I, Robert N. Stephens, certify that, to the best of my knowledge based upon a review of the Quarterly Report on Form 10-Q of Adaptec, Inc. for the three months ended June 30, 2002 (the "Form 10-Q"), the Form 10-Q fully complies with the requirements of Section 13(a) of the Securities Exchange Act of 1934, as amended, and that information contained in the Form 10-Q fairly presents, in all material respects, the financial condition and results of operations of Adaptec, Inc. for the quarterly periods covered by the Form 10-Q.

Date: August 12, 2002 By:  /s/  ROBERT N. STEPHENS Robert N. Stephens
President and Chief Executive Officer,
Adaptec, Inc.

        I, David A. Young, certify that, to the best of my knowledge based upon a review of the Form 10-Q, the Form 10-Q fully complies with the requirements of Section 13(a) of the Securities Exchange Act of 1934, as amended, and that information contained in the Form 10-Q fairly presents, in all material respects, the financial condition and results of operations of Adaptec, Inc. for the quarterly periods covered by the Form 10-Q.

Date: August 12, 2002 By:  /s/  DAVID A. YOUNG David A. Young
Vice President and Chief Financial Officer,
Adaptec, Inc.

QuickLinks

Exhibit 99.1