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                                                                    EXHIBIT 3.1



                AMENDED AND RESTATED CERTIFICATE OF INCORPORATION
                             OF KOMAG, INCORPORATED,
                             A DELAWARE CORPORATION



        The undersigned, T.H. Tan and Edward H. Siegler, hereby certify that:

        FIRST: They are the duly elected and acting President and Secretary,
respectively, of Komag, Incorporated.

        SECOND: The Certificate of Incorporation of said corporation was
originally filed with the Secretary of State of Delaware on October 29, 1986
under the name Komag Delaware, Inc.

        THIRD: Pursuant to Section 242 and 245 of the General Corporation Law of
the State of Delaware, the Certificate of Incorporation of said corporation is
hereby amended and restated to read in full as follows:

                                    ARTICLE I

        The name of the corporation (herein called the "Corporation") is KOMAG,
INCORPORATED.

                                   ARTICLE II

        The address of the registered office of the Corporation in the State of
Delaware is Corporation Trust Center, 1209 Orange Street, in the City of
Wilmington, County of New Castle, zip code 19801. The name of the registered
agent of the Corporation at such address is The Corporation Trust Company.

                                  ARTICLE III

        The purpose of the Corporation is to engage in any lawful act or
activity for which corporations may be organized under the General Corporation
Law of the State of Delaware.

                                   ARTICLE IV

        The Corporation shall be authorized to issue Two Hundred Fifty-One
Million (251,000,000) shares of capital stock having an aggregate par value of
Two Million Five Hundred Ten Thousand Dollars ($2,510,000). This Capital Stock
shall be divided into two classes, Common Stock and Preferred Stock, both
classes having a par value. The authorized Common Stock shall be Two Hundred
Fifty Million shares (250,000,000) shares having a par value of one cent ($.01)
per share for an aggregate class par value of Two Million Five Hundred Thousand
Dollars ($2,500,000). The authorized Preferred Stock shall be One Million
(1,000,000) shares having a par value of one cent ($.01) per share for an
aggregate class par value of Ten Thousand Dollars ($10,000). The Board of



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Directors of the corporation is hereby empowered (i) to determine the
preferences, privileges, or restrictions of such Preferred Stock, including (but
not limited to) the dividend rights and rate, conversion and voting rights,
redemption rights and the terms and prices thereof (including any provision for
a sinking fund), or liquidation preferences thereof, if any, (ii) to divide the
Preferred Stock into different series consisting of any number of shares, each
series having different rights, provisions, or conditions from any other series
and (iii) to increase or decrease the number of shares of any series so
designated, but not below the number of shares of any such series then
outstanding. The Corporation is also authorized to issue debentures (convertible
into the Common Stock or Preferred Stock or non-convertible, either with or
without voting rights) and/or warrants or options to purchase Common stock or
Preferred Stock.

                                    ARTICLE V

        In the furtherance and not in limitation of the powers conferred by
statute, the Board of Directors is expressly authorized to make, alter, amend or
repeal the By-Laws of the Corporation.

                                   ARTICLE VI

        The number of directors of the Corporation shall be fixed from time to
time by a by-law or amendment thereof duly adopted by the Board of Directors or
by the Stockholders.

                                   ARTICLE VII

        All rights to vote and all voting power shall be vested in the Common
Stock, and any Preferred Stock with voting rights pursuant to the terms thereof,
and any such holders thereof shall be entitled at all elections of directors to
as many votes as shall equal the number of votes which (except for this
provision as to cumulative voting) he would be entitled to cast for the election
of directors with respect to his shares of stock multiplied by the number of
directors to be elected, and such holder may cast all of such votes for a single
director or may distribute them among the number to be voted for, or for any two
or more of them as he may see fit, and to vote for each share upon all other
matters.

                                  ARTICLE VIII

        Elections of directors need not be by written ballot unless the By-laws
of the Corporation shall be provided.

                                   ARTICLE IX

        Meetings of stockholders may be held within or without the State of
Delaware, as the By-laws may provide. The books of the Corporation may be kept
(subject to any provision contained in the statutes) outside the State of
Delaware at such place or places as may be designated from time to time by the
Board of Directors or in the By-laws of the Corporation.

                                   ARTICLE X




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        A director of the Corporation shall not be personally liable to the
Corporation or its stockholders for monetary damages for breach of fiduciary
duty as a director, except for liability (i) for any breach of the director's
duty of loyalty to the Corporation or its stockholders, (ii) for acts or
omissions not in good faith or which involve intentional misconduct or knowing
violation of law, (iii) under Section 174 of the Delaware General Corporation
Law, or (iv) for any transaction from which the director derived any improper
personal benefit.

                                   ARTICLE XI

        The Corporation reserves the right to amend, alter, change or repeal any
provision contained in this restated Certificate of Incorporation, in the manner
now or hereafter prescribed by statute, and all rights conferred upon
stockholders herein are granted subject to this reservation.

                                   ARTICLE XII

        The Corporation reserves the right to amend, alter, change or repeal any
provision contained in this Amended and Restated Certificate of Incorporation,
in the manner now or hereafter prescribed by statue, and all rights conferred
upon stockholders herein are granted subject to this reservation.

                                  ARTICLE XIII

        The Corporation shall have perpetual existence.

        FOURTH: The foregoing Amended and Restated Certificate of Incorporation
has been duly adopted by the Corporation's Board of Directors and stockholders
in accordance with the applicable provisions of Sections 242 and 245 of the
General Corporation Law of the State of Delaware.

        IN WITNESS WHEREOF, the undersigned have executed this certificate on
November__, 2000.



                                              KOMAG, INCORPORATED

                                              By:
                                                 ------------------------------
                                                 T.H. Tan, President



Attest:
        ------------------------------
        Edward H. Siegler, Secretary



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