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                                                                     Exhibit 5.1
                                                    

                                 March 26, 1998


Adaptec, Inc.
691 South Milpitas Boulevard
Milpitas, California 95035

         RE: REGISTRATION STATEMENT ON FORM S-8

Gentlemen:

         We have examined the Registration Statement on Form S-8 to be filed by
Adaptec, Inc., a Delaware Corporation (the "Company"), with the Securities and
Exchange Commission on or about March 26, 1998 (the "Registration Statement") in
connection with the assumption pursuant to Rule 414 of the Securities Act of
1933, as amended, by the Company of that certain Registration Statement on Form
S-8 filed by the Company's predecessor, Adaptec, Inc., a California Corporation
("Adaptec California"), relating to shares of Common Stock of Adaptec California
reserved for issuance under the 1986 Employee Stock Purchase Plan (the "Plan")
of Adaptec California. We understand that the Plans have been assumed by the
Company and that in accordance with the terms of the Plans, the Company has
reserved shares (the "Shares") of Common Stock of the Company for issuance
pursuant to the Plans. As your counsel, we have examined the proceedings taken
and are familiar with the proceedings proposed to be taken by you in connection
with said issuance and sale of the Shares pursuant to the Plan.

         It is our opinion that, upon completion of the proceedings being taken
or contemplated by us to be taken prior to the issuance and sale of the Shares
pursuant to the Plan, and upon completion of the proceedings being taken in
order to permit such transaction to be carried out in accordance with the
securities laws of the various states where required, the Shares, when issued
and sold in the manner referred to in the Plan and the Registration Statement,
will be legally and validly issued, 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