<PAGE>   1
The Index to Exhibits is on Page 7 of this document.

      As filed with the Securities and Exchange Commission on June 30, 1998
                                               Registration No. 333-____________
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549


                                    FORM S-8
                             REGISTRATION STATEMENT
                                      Under
                           THE SECURITIES ACT OF 1933


                                  ADAPTEC, INC.
             (Exact name of registrant as specified in its charter)


       Delaware                                         94-2748530
(State of Incorporation)                    (I.R.S. Employer Identification No.)

                          691 South Milpitas Boulevard
                           Milpitas, California 95035
                    (Address of principal executive offices)


                          ADAPTEC, INC. 1990 STOCK PLAN
                 RIDGE TECHNOLOGIES, INC. 1997 STOCK OPTION PLAN
                            (Full title of the Plan)


                                F. GRANT SAVIERS
                             Chief Executive Officer
                                  ADAPTEC, INC.
                          691 South Milpitas Boulevard
                           Milpitas, California 95035
                                 (408) 945-8600
            (Name, address and telephone number of agent for service)


                                   Copies to:
                           HENRY P. MASSEY, JR., ESQ.
                        Wilson Sonsini Goodrich & Rosati
                            Professional Corporation
                               650 Page Mill Road
                        Palo Alto, California 94304-1050
                                 (650) 493-9300

================================================================================

<PAGE>   2

<TABLE>
<CAPTION>
                                     CALCULATION OF REGISTRATION FEE
==========================================================================================================
                                                         Proposed          Proposed
             Title of                                     Maximum           Maximum
            Securities                  Amount           Offering          Aggregate         Amount of
              to be                      to be             Price           Offering        Registration
            Registered               Registered (1)       Per Share           Price              Fee
---------------------------------- ----------------- ----------------- ----------------- -----------------
<S>                                <C>               <C>               <C>               <C>       
Common Stock 
$.001 par value, to be issued 
under the Adaptec, Inc.
  1990 Stock Plan                          9,584,899         $15.94(2)   $152,783,290.00        $45,071.07
---------------------------------- ----------------- ----------------- ----------------- -----------------
Common Stock
  $.001 par value, to be issued
   under the Ridge Technologies,
   Inc. 1997 Stock Option Plan             1,720,000         $17.38(3)   $ 29,893,600.00         $8,818.61
================================== ================= ================= ================= =================
Total                                     11,304,899                     $182,676,890.00        $53,889.68
================================== ================= ================= ================= =================
</TABLE>

(1)      For the sole purpose of calculating the registration fee, the number of
         shares to be registered under this Registration Statement is the number
         of additional shares authorized to be issued under the Adaptec, Inc.
         1990 Stock Plan and the number of shares subject to options currently
         issued and outstanding under the Ridge Technologies, Inc. 1997 Stock
         Option Plan. Adaptec, Inc. (the "Registrant") acquired all of the
         outstanding capital stock of Ridge Technologies, Inc. ("Ridge") on May
         21, 1998 (the "Ridge Acquisition"). Pursuant to the terms of the Ridge
         Acquisition, the Registrant assumed all outstanding options to purchase
         Ridge Common Stock under the Ridge 1997 Stock Option Plan (the "Assumed
         Options"), and such options became options to purchase the Registrant's
         Common Stock, subject to certain adjustments as to number of shares and
         exercise price.

(2)      Estimated in accordance with Rule 457(h) under the Securities Act of
         1933, as amended (the "Securities Act") solely for the purpose of
         calculating the registration fee. Computation based upon the average of
         the high and low prices of the Registrant's Common Stock as reported on
         The Nasdaq National Market on June 24, 1998 because the price at which
         options to be granted in the future may be exercised is not currently
         determinable.

(3)      Pursuant to the terms of the Ridge Acquisition, the per share exercise
         price of the Assumed Options was amended to $17.38, the closing sale
         price of the Registrant's Common Stock as reported on The Nasdaq
         National Market on May 20, 1998.


<PAGE>   3

           PART II: INFORMATION REQUIRED IN THE REGISTRATION STATEMENT


ITEM 3. Information Incorporated by Reference

               The following documents and information heretofore filed with the
Securities and Exchange Commission (the "Commission") are hereby incorporated by
reference:

         (a)      The Registrant's Annual Report on Form 10-K, Commission file
                  no. 0-15071, filed on June 26, 1998.

         (b)      Not applicable.

         (c)      Items 1 and 2 of the Registrant's Registration Statement
                  Amendment on Form 8-A filed on July 20, 1992 pursuant to
                  Section 12 of the Securities and Exchange Act of 1934, as
                  amended (the "Exchange Act").

                  Exhibit 1 to Amendment No. 4 on Form 8-A (filed on January 14,
                  1997) to the Registrant's Registration Statement on Form 8-A,
                  Commission file no. 0-15071, filed on May 11, 1989.

               All documents subsequently filed by the Registrant pursuant to
Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of
a post-effective amendment which indicates that all securities offered have been
sold or which deregisters all securities then remaining unsold, shall be deemed
to be incorporated by reference in this Registration Statement and to be part
hereof from the date of filing of such documents.

ITEM 4. Description of Securities

         Not applicable.

ITEM 5. Interests of Named Experts and Counsel

         Not applicable.

ITEM 6. Indemnification of Directors and Officers

               The Company's Certificate of Incorporation limits the liability
of directors to the maximum extent permitted by Delaware law. Delaware law
provides that directors of a corporation will not be personally liable for
monetary damages for breach of their fiduciary duties as directors, except for
liability (i) for any breach of their duty of loyalty to the corporation or its
stockholders, (ii) for acts or omissions not in good faith or that involve
intentional misconduct or a knowing violation of law, (iii) for unlawful
payments of dividends or unlawful stock repurchases or redemptions as provided
in Section 174 of the Delaware General Corporation Law, or (iv) for any
transaction from which the director derived an improper personal benefit.



                                        1

<PAGE>   4

               The Company's Bylaws provide that the Company shall indemnify its
directors and officers and may indemnify its employees and other agents to the
fullest extent permitted by law. The Company's Bylaws also permit the Company to
secure insurance on behalf of any officer, director, employee or other agent for
any liability arising out of his or her actions in such capacity, regardless of
whether the Company would have the power to indemnify him or her against such
liability under the General Corporation Law of Delaware. The Company currently
has secured such insurance on behalf of its officers and directors.

               The Company has entered into agreements to indemnify its
directors and officers, in addition to indemnification provided for in the
Company's Bylaws. Subject to certain conditions, these agreements, among other
things, indemnify the Company's directors and officers for certain expenses
(including attorneys' fees), judgments, fines and settlement amounts incurred by
any such person in any action or proceeding, including any action by or in the
right of the Company, arising out of such person's services as a director or
officer of the Company, any subsidiary of the Company or any other company or
enterprise to which the person provides services at the request of the Company.

ITEM 7. Exemption From Registration Claimed

         Not applicable.

<TABLE>
<CAPTION>
ITEM 8.  Exhibits
         --------
<S>      <C>                                                               
         4.1(1)   Second Amended and Restated Rights Agreement, dated as of
                  December 5, 1996 between Adaptec, Inc. and ChaseMellon
                  Shareholder Services, LLC, New York, NY, including the
                  Certificate of Determination, the form of Rights Certificate
                  and the Summary of Rights attached thereto as Exhibits A, B
                  and C, respectively.

         4.2(2)   First Amendment, dated March 12, 1998, to the Second Amended
                  and Restated Rights Agreement, dated as of December 5, 1996
                  between Adaptec, Inc. and ChaseMellon Shareholder Services,
                  LLC, New York, NY, including the Certificate of Determination,
                  the form of Rights Certificate and the Summary of Rights
                  attached thereto as Exhibits A, B and C, respectively.

         5.1      Opinion of Wilson Sonsini Goodrich & Rosati, Professional
                  Corporation, as to legality of securities being registered.

         23.1     Consent of Independent Accountants.

         23.2     Consent of Wilson Sonsini Goodrich & Rosati, Professional
                  Corporation (see Exhibit 5.1).

         24.1     Power of Attorney (see Page 4).
</TABLE>

---------------

         (1)      Incorporated by reference to Exhibit 1 to Amendment No. 4 on
                  Form 8-A (filed January 14, 1997) to the Registrant's
                  Registration Statement (Commission File No. 0-15071) on Form
                  8-A filed with the Commission on May 11, 1989.


                                        2

<PAGE>   5



         (2)      Incorporated by reference to Exhibit 4.2 to the Registrant's
                  Annual Report on Form 10-K, Commission file no. 0-15071, filed
                  on June 26, 1998.

ITEM 9. Undertakings

        A.     The undersigned Registrant hereby undertakes:

               (1) To file, during any period in which offers or sales are being
made, a post-effective amendment to this Registration Statement to include any
material information with respect to the plan of distribution not previously
disclosed in the Registration Statement or any material change to such
information in the Registration Statement.

               (2) That, for the purpose of determining any liability under the
Securities Act, each such post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

               (3) To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

        B. The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or Sec tion 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to Section 15(d) of the Exchange Act) that is
incorporated by reference in the Registration Statement shall be deemed to be a
new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

        C. Insofar as indemnification for liabilities arising under the
Securities Act may be permitted to directors, officers and controlling persons
of the Registrant pursuant to the foregoing provisions, or otherwise, the
Registrant has been advised that in the opinion of the Commission such
indemnification is against public policy as expressed in the Securities Act and
is, therefore, unenforceable. In the event that a claim for indemnification
against such liabilities (other than the payment by the Registrant of expenses
incurred or paid by a director, officer or controlling person of the Registrant
in the successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.



                                        3

<PAGE>   6

                                   SIGNATURES

        Pursuant to the requirements of the Securities Act, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Milpitas, State of California, on the 26th day of
June, 1998.

                                        ADAPTEC, INC.

                                        By: /s/ F. GRANT SAVIERS
                                           -------------------------------------
                                           F. Grant Saviers
                                           Chief Executive Officer and Director

                                POWER OF ATTORNEY

        KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints F. Grant Saviers and Paul G. Hansen,
jointly and severally, as his attorneys-in-fact, each with the power of
substitution, for him in any and all capacities, to sign any amendments to this
Registration Statement on Form S-8, and to file the same, with exhibits thereto
and other documents in connection therewith, with the Securities and Exchange
Commission, hereby ratifying and confirming all that each of said
attorneys-in-fact, or his substitute or substitutes may do or cause to be done
by virtue hereof.

        Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the date indicated.




<TABLE>
<CAPTION>
          NAME                                       TITLE                                    DATE
---------------------------       ------------------------------------------------    --------------------
<S>                               <C>                                                 <C> 
/s/ F. GRANT SAVIERS              Chief Executive Officer and Director                    June 26, 1998
--------------------------
F. Grant Saviers

/s/ PAUL G. HANSEN                Vice President, Finance, Chief Financial Officer        June 29, 1998
--------------------------
Paul G. Hansen                    (Principal Financial Officer)

/s/ ANDREW J. BROWN               Vice President, Corporate Controller (Principal         June 29, 1998
--------------------------
Andrew J. Brown                   Accounting Officer)

                                  Director                                                June __, 1998
--------------------------
Laurence B. Boucher

/s/ CARL J. CONTI                 Director                                                June 28, 1998
--------------------------
Carl J. Conti

                                  Director                                                June __, 1998
--------------------------
John East

                                  Director                                                June __, 1998
--------------------------
Ilene H. Lang

/s/ ROBERT J. LOARIE              Director                                                June 29, 1998
--------------------------
Robert J. Loarie

</TABLE>


                                        4

<PAGE>   7

<TABLE>
<CAPTION>
          NAME                                       TITLE                                  DATE
---------------------------       ------------------------------------------------    ------------------
<S>                               <C>                                                 <C> 
/s/ B.J. MOORE                    Director                                            June 28, 1998
--------------------------
B.J. Moore

/s/ W. FERRELL SANDERS            Director                                           June 26, 1998
--------------------------
W. Ferrell Sanders

                                  Director                                           June __, 1998
--------------------------
Phillip E. White

</TABLE>


                                        5

<PAGE>   8



                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549


             ------------------------------------------------------

                                    EXHIBITS
             ------------------------------------------------------


                       Registration Statement on Form S-8

                                  ADAPTEC, INC.

                                  June 30, 1998


                                        6

<PAGE>   9



                                         INDEX TO EXHIBITS



<TABLE>
<CAPTION>
        Exhibit                                                                               Page
        Number                                                                                 No.
        ------                                                                                 ---
<S>            <C>                                                                            <C>
        4.1(1) Second Amended and Restated Rights Agreement, dated as of
               December 5, 1996 between Adaptec, Inc. and ChaseMellon
               Shareholder Services, LLC, New York, NY, including the
               Certificate of Determination, the form of Rights Certificate and
               the Summary of Rights attached thereto as Exhibits A, B and C,
               respectively.

        4.2(2) First Amendment, dated March 12, 1998, to the Second Amended and
               Restated Rights Agreement, dated as of December 5, 1996 between
               Adaptec, Inc. and ChaseMellon Shareholder Services, LLC, New
               York, NY, including the Certificate of Determination, the form of
               Rights Certificate and the Summary of Rights attached thereto as
               Exhibits A, B and C, respectively.

        5.1    Opinion of Wilson Sonsini Goodrich & Rosati, Professional
               Corporation, as to legality of securities being registered.

        23.1   Consent of Independent Accountants.

        23.2   Consent of Wilson Sonsini Goodrich & Rosati, Professional
               Corporation (see Exhibit 5.1).

        24.1 Power of Attorney (see Page 4).
</TABLE>

------------

        (1)    Incorporated by reference to Exhibit 1 to Amendment No. 4 on Form
               8-A (filed January 14, 1997) to the Registrant's Registration
               Statement (Commission File No. 0-15071) on Form 8-A filed with
               the Commission on May 11, 1989.

        (2)    Incorporated by reference to Exhibit 4.2 to the Registrant's
               Annual Report on Form 10-K (Commission file no. 0-15071) filed
               with the Commission on June 26, 1998.


                                        7
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1
The Index to Exhibits is on Page 7 of this document.

      As filed with the Securities and Exchange Commission on June 30, 1998
                                               Registration No. 333-____________
================================================================================

                       SECURITIES AND EXCHANGE COMMISSION
                             Washington, D.C. 20549

                                    FORM S-8
                             REGISTRATION STATEMENT
                                      Under
                           THE SECURITIES ACT OF 1933

                                  ADAPTEC, INC.
             (Exact name of registrant as specified in its charter)

       Delaware                                         94-2748530
(State of Incorporation)                    (I.R.S. Employer Identification No.)

                          691 South Milpitas Boulevard
                           Milpitas, California 95035
                    (Address of principal executive offices)

                          ADAPTEC, INC. 1990 STOCK PLAN
                 RIDGE TECHNOLOGIES, INC. 1997 STOCK OPTION PLAN
                            (Full title of the Plan)

                                F. GRANT SAVIERS
                             Chief Executive Officer
                                  ADAPTEC, INC.
                          691 South Milpitas Boulevard
                           Milpitas, California 95035
                                 (408) 945-8600
            (Name, address and telephone number of agent for service)

                                   Copies to:
                           HENRY P. MASSEY, JR., ESQ.
                        Wilson Sonsini Goodrich & Rosati
                            Professional Corporation
                               650 Page Mill Road
                        Palo Alto, California 94304-1050
                                 (650) 493-9300

================================================================================
2
CALCULATION OF REGISTRATION FEE
==========================================================================================================
                                                         Proposed          Proposed
             Title of                                     Maximum           Maximum
            Securities                  Amount           Offering          Aggregate         Amount of
              to be                      to be             Price           Offering        Registration
            Registered               Registered (1)       Per Share           Price              Fee
---------------------------------- ----------------- ----------------- ----------------- -----------------
Common Stock 
$.001 par value, to be issued 
under the Adaptec, Inc.
  1990 Stock Plan                          9,584,899         $15.94(2)   $152,783,290.00        $45,071.07
---------------------------------- ----------------- ----------------- ----------------- -----------------
Common Stock
  $.001 par value, to be issued
   under the Ridge Technologies,
   Inc. 1997 Stock Option Plan             1,720,000         $17.38(3)   $ 29,893,600.00         $8,818.61
================================== ================= ================= ================= =================
Total                                     11,304,899                     $182,676,890.00        $53,889.68
================================== ================= ================= ================= =================
(1)      For the sole purpose of calculating the registration fee, the number of
         shares to be registered under this Registration Statement is the number
         of additional shares authorized to be issued under the Adaptec, Inc.
         1990 Stock Plan and the number of shares subject to options currently
         issued and outstanding under the Ridge Technologies, Inc. 1997 Stock
         Option Plan. Adaptec, Inc. (the "Registrant") acquired all of the
         outstanding capital stock of Ridge Technologies, Inc. ("Ridge") on May
         21, 1998 (the "Ridge Acquisition"). Pursuant to the terms of the Ridge
         Acquisition, the Registrant assumed all outstanding options to purchase
         Ridge Common Stock under the Ridge 1997 Stock Option Plan (the "Assumed
         Options"), and such options became options to purchase the Registrant's
         Common Stock, subject to certain adjustments as to number of shares and
         exercise price.

(2)      Estimated in accordance with Rule 457(h) under the Securities Act of
         1933, as amended (the "Securities Act") solely for the purpose of
         calculating the registration fee. Computation based upon the average of
         the high and low prices of the Registrant's Common Stock as reported on
         The Nasdaq National Market on June 24, 1998 because the price at which
         options to be granted in the future may be exercised is not currently
         determinable.

(3)      Pursuant to the terms of the Ridge Acquisition, the per share exercise
         price of the Assumed Options was amended to $17.38, the closing sale
         price of the Registrant's Common Stock as reported on The Nasdaq
         National Market on May 20, 1998.
3

           PART II: INFORMATION REQUIRED IN THE REGISTRATION STATEMENT

ITEM 3. Information Incorporated by Reference

               The following documents and information heretofore filed with the
Securities and Exchange Commission (the "Commission") are hereby incorporated by
reference:

         (a)      The Registrant's Annual Report on Form 10-K, Commission file
                  no. 0-15071, filed on June 26, 1998.

         (b)      Not applicable.

         (c)      Items 1 and 2 of the Registrant's Registration Statement
                  Amendment on Form 8-A filed on July 20, 1992 pursuant to
                  Section 12 of the Securities and Exchange Act of 1934, as
                  amended (the "Exchange Act").

                  Exhibit 1 to Amendment No. 4 on Form 8-A (filed on January 14,
                  1997) to the Registrant's Registration Statement on Form 8-A,
                  Commission file no. 0-15071, filed on May 11, 1989.

               All documents subsequently filed by the Registrant pursuant to
Sections 13(a), 13(c), 14 and 15(d) of the Exchange Act, prior to the filing of
a post-effective amendment which indicates that all securities offered have been
sold or which deregisters all securities then remaining unsold, shall be deemed
to be incorporated by reference in this Registration Statement and to be part
hereof from the date of filing of such documents.

ITEM 4. Description of Securities

         Not applicable.

ITEM 5. Interests of Named Experts and Counsel

         Not applicable.

ITEM 6. Indemnification of Directors and Officers

               The Company's Certificate of Incorporation limits the liability
of directors to the maximum extent permitted by Delaware law. Delaware law
provides that directors of a corporation will not be personally liable for
monetary damages for breach of their fiduciary duties as directors, except for
liability (i) for any breach of their duty of loyalty to the corporation or its
stockholders, (ii) for acts or omissions not in good faith or that involve
intentional misconduct or a knowing violation of law, (iii) for unlawful
payments of dividends or unlawful stock repurchases or redemptions as provided
in Section 174 of the Delaware General Corporation Law, or (iv) for any
transaction from which the director derived an improper personal benefit.

                                        1
4

               The Company's Bylaws provide that the Company shall indemnify its
directors and officers and may indemnify its employees and other agents to the
fullest extent permitted by law. The Company's Bylaws also permit the Company to
secure insurance on behalf of any officer, director, employee or other agent for
any liability arising out of his or her actions in such capacity, regardless of
whether the Company would have the power to indemnify him or her against such
liability under the General Corporation Law of Delaware. The Company currently
has secured such insurance on behalf of its officers and directors.

               The Company has entered into agreements to indemnify its
directors and officers, in addition to indemnification provided for in the
Company's Bylaws. Subject to certain conditions, these agreements, among other
things, indemnify the Company's directors and officers for certain expenses
(including attorneys' fees), judgments, fines and settlement amounts incurred by
any such person in any action or proceeding, including any action by or in the
right of the Company, arising out of such person's services as a director or
officer of the Company, any subsidiary of the Company or any other company or
enterprise to which the person provides services at the request of the Company.

ITEM 7. Exemption From Registration Claimed

         Not applicable.
ITEM 8.  Exhibits
         --------
4.1(1)   Second Amended and Restated Rights Agreement, dated as of
                  December 5, 1996 between Adaptec, Inc. and ChaseMellon
                  Shareholder Services, LLC, New York, NY, including the
                  Certificate of Determination, the form of Rights Certificate
                  and the Summary of Rights attached thereto as Exhibits A, B
                  and C, respectively.

         4.2(2)   First Amendment, dated March 12, 1998, to the Second Amended
                  and Restated Rights Agreement, dated as of December 5, 1996
                  between Adaptec, Inc. and ChaseMellon Shareholder Services,
                  LLC, New York, NY, including the Certificate of Determination,
                  the form of Rights Certificate and the Summary of Rights
                  attached thereto as Exhibits A, B and C, respectively.

         5.1      Opinion of Wilson Sonsini Goodrich & Rosati, Professional
                  Corporation, as to legality of securities being registered.

         23.1     Consent of Independent Accountants.

         23.2     Consent of Wilson Sonsini Goodrich & Rosati, Professional
                  Corporation (see Exhibit 5.1).

         24.1     Power of Attorney (see Page 4).
---------------

         (1)      Incorporated by reference to Exhibit 1 to Amendment No. 4 on
                  Form 8-A (filed January 14, 1997) to the Registrant's
                  Registration Statement (Commission File No. 0-15071) on Form
                  8-A filed with the Commission on May 11, 1989.

                                        2
5

         (2)      Incorporated by reference to Exhibit 4.2 to the Registrant's
                  Annual Report on Form 10-K, Commission file no. 0-15071, filed
                  on June 26, 1998.

ITEM 9. Undertakings

        A.     The undersigned Registrant hereby undertakes:

               (1) To file, during any period in which offers or sales are being
made, a post-effective amendment to this Registration Statement to include any
material information with respect to the plan of distribution not previously
disclosed in the Registration Statement or any material change to such
information in the Registration Statement.

               (2) That, for the purpose of determining any liability under the
Securities Act, each such post-effective amendment shall be deemed to be a new
registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

               (3) To remove from registration by means of a post-effective
amendment any of the securities being registered which remain unsold at the
termination of the offering.

        B. The undersigned Registrant hereby undertakes that, for purposes of
determining any liability under the Securities Act, each filing of the
Registrant's annual report pursuant to Section 13(a) or Sec tion 15(d) of the
Exchange Act (and, where applicable, each filing of an employee benefit plan's
annual report pursuant to Section 15(d) of the Exchange Act) that is
incorporated by reference in the Registration Statement shall be deemed to be a
new registration statement relating to the securities offered therein, and the
offering of such securities at that time shall be deemed to be the initial bona
fide offering thereof.

        C. Insofar as indemnification for liabilities arising under the
Securities Act may be permitted to directors, officers and controlling persons
of the Registrant pursuant to the foregoing provisions, or otherwise, the
Registrant has been advised that in the opinion of the Commission such
indemnification is against public policy as expressed in the Securities Act and
is, therefore, unenforceable. In the event that a claim for indemnification
against such liabilities (other than the payment by the Registrant of expenses
incurred or paid by a director, officer or controlling person of the Registrant
in the successful defense of any action, suit or proceeding) is asserted by such
director, officer or controlling person in connection with the securities being
registered, the Registrant will, unless in the opinion of its counsel the matter
has been settled by controlling precedent, submit to a court of appropriate
jurisdiction the question whether such indemnification by it is against public
policy as expressed in the Securities Act and will be governed by the final
adjudication of such issue.

                                        3
6

                                   SIGNATURES

        Pursuant to the requirements of the Securities Act, the Registrant
certifies that it has reasonable grounds to believe that it meets all of the
requirements for filing on Form S-8 and has duly caused this Registration
Statement to be signed on its behalf by the undersigned, thereunto duly
authorized, in the City of Milpitas, State of California, on the 26th day of
June, 1998.

                                        ADAPTEC, INC.

                                        By: /s/ F. GRANT SAVIERS
                                           -------------------------------------
                                           F. Grant Saviers
                                           Chief Executive Officer and Director

                                POWER OF ATTORNEY

        KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature
appears below constitutes and appoints F. Grant Saviers and Paul G. Hansen,
jointly and severally, as his attorneys-in-fact, each with the power of
substitution, for him in any and all capacities, to sign any amendments to this
Registration Statement on Form S-8, and to file the same, with exhibits thereto
and other documents in connection therewith, with the Securities and Exchange
Commission, hereby ratifying and confirming all that each of said
attorneys-in-fact, or his substitute or substitutes may do or cause to be done
by virtue hereof.

        Pursuant to the requirements of the Securities Act of 1933, this
Registration Statement has been signed by the following persons in the
capacities and on the date indicated.
NAME                                       TITLE                                    DATE
---------------------------       ------------------------------------------------    --------------------
/s/ F. GRANT SAVIERS              Chief Executive Officer and Director                    June 26, 1998
--------------------------
F. Grant Saviers

/s/ PAUL G. HANSEN                Vice President, Finance, Chief Financial Officer        June 29, 1998
--------------------------
Paul G. Hansen                    (Principal Financial Officer)

/s/ ANDREW J. BROWN               Vice President, Corporate Controller (Principal         June 29, 1998
--------------------------
Andrew J. Brown                   Accounting Officer)

                                  Director                                                June __, 1998
--------------------------
Laurence B. Boucher

/s/ CARL J. CONTI                 Director                                                June 28, 1998
--------------------------
Carl J. Conti

                                  Director                                                June __, 1998
--------------------------
John East

                                  Director                                                June __, 1998
--------------------------
Ilene H. Lang

/s/ ROBERT J. LOARIE              Director                                                June 29, 1998
--------------------------
Robert J. Loarie
4
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NAME                                       TITLE                                  DATE
---------------------------       ------------------------------------------------    ------------------
/s/ B.J. MOORE                    Director                                            June 28, 1998
--------------------------
B.J. Moore

/s/ W. FERRELL SANDERS            Director                                           June 26, 1998
--------------------------
W. Ferrell Sanders

                                  Director                                           June __, 1998
--------------------------
Phillip E. White
5
8

                       SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549

             ------------------------------------------------------

                                    EXHIBITS
             ------------------------------------------------------

                       Registration Statement on Form S-8

                                  ADAPTEC, INC.

                                  June 30, 1998

                                        6
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                                         INDEX TO EXHIBITS
Exhibit                                                                               Page
        Number                                                                                 No.
        ------                                                                                 ---
4.1(1) Second Amended and Restated Rights Agreement, dated as of
               December 5, 1996 between Adaptec, Inc. and ChaseMellon
               Shareholder Services, LLC, New York, NY, including the
               Certificate of Determination, the form of Rights Certificate and
               the Summary of Rights attached thereto as Exhibits A, B and C,
               respectively.

        4.2(2) First Amendment, dated March 12, 1998, to the Second Amended and
               Restated Rights Agreement, dated as of December 5, 1996 between
               Adaptec, Inc. and ChaseMellon Shareholder Services, LLC, New
               York, NY, including the Certificate of Determination, the form of
               Rights Certificate and the Summary of Rights attached thereto as
               Exhibits A, B and C, respectively.

        5.1    Opinion of Wilson Sonsini Goodrich & Rosati, Professional
               Corporation, as to legality of securities being registered.

        23.1   Consent of Independent Accountants.

        23.2   Consent of Wilson Sonsini Goodrich & Rosati, Professional
               Corporation (see Exhibit 5.1).

        24.1 Power of Attorney (see Page 4).
------------

        (1)    Incorporated by reference to Exhibit 1 to Amendment No. 4 on Form
               8-A (filed January 14, 1997) to the Registrant's Registration
               Statement (Commission File No. 0-15071) on Form 8-A filed with
               the Commission on May 11, 1989.

        (2)    Incorporated by reference to Exhibit 4.2 to the Registrant's
               Annual Report on Form 10-K (Commission file no. 0-15071) filed
               with the Commission on June 26, 1998.

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