Exhibit 10.4.2

                               KOMAG, INCORPORATED
                              MANAGEMENT BONUS PLAN

                    AS AMENDED AND RESTATED JANUARY 22, 1997


       I.         PURPOSES OF THE PLAN

                  1.01 The Komag, Incorporated ("Company") Management Bonus Plan
("Plan") is  established  to promote the interests of the Company by creating an
incentive  program to (i)  attract  and  retain  employees  who will  strive for
excellence, and (ii) motivate those individuals to set and achieve above-average
objectives  by providing  them with rewards for  contributions  to the operating
profits and earning power of the Company.

      II.         ADMINISTRATION OF THE PLAN

                  2.01 The Plan is  hereby  adopted  by the  Company's  Board of
Directors (the "Board"),  subject to the approval of the Company's  stockholders
at the 1997  Annual  Stockholders  Meeting,  and  shall be  administered  by the
Compensation Committee  ("Committee") of the Board. The members of the Committee
shall at all times satisfy the  requirements  established for outside  directors
under  Internal  Revenue  Code  Section  162(m)  and  the  applicable   Treasury
Regulations.

                  2.02 The  interpretation  and construction of the Plan and the
adoption of rules and  regulations for  administering  the Plan shall be made by
the  Committee.  Decisions  of the  Committee  shall be final and binding on all
parties who have an interest in the Plan.

                  2.03  Within 90 days after the start of each of the  Company's
fiscal years, the Committee will determine which of the Company's  subsidiaries,
if any, will participate in the Plan for such fiscal year.

     III.         DETERMINATION OF PARTICIPANTS

                  3.01 An  individual  shall be eligible to  participate  in the
Plan if employed by the Company or any of its  participating  subsidiaries for a
period  of not less  than six (6)  consecutive  months  at the time the bonus is
earned under Article IV, is in job grade E06 or above,  and remains eligible for
a bonus award under the terms of Section 4.01 or 4.03. An individual who is on a
leave of absence or whose employment

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terminates  and is then re-hired in the same fiscal year shall remain  eligible,
but his or her bonus award shall be adjusted, as provided in Article IV below.

                  3.02              For purposes of the Plan:

                                    A.      Except as set forth in Section 3.01,
an individual  shall be  considered  an employee for so long as such  individual
remains employed by the Company or one or more subsidiary corporations.

                                    B.      Each  corporation  (other  than  the
Company) in an unbroken chain of  corporations  beginning with the Company shall
be considered to be a subsidiary of the Company,  provided each such corporation
(other than the last  corporation  in the unbroken  chain) owns,  at the time of
determination,  stock  possessing  more than fifty percent of the total combined
voting  power of all classes of stock in one of the other  corporations  in such
chain.

      IV.         BONUS AWARDS

                  4.01 No  eligible  employee  shall earn any portion of a bonus
award made hereunder for any fiscal year until the last day of that fiscal year,
and then only if there has been an allocation of a portion of the bonus pool for
such fiscal year to that employee in accordance with the procedures set forth in
Section 4.03. If an eligible employee receives no allocation under Section 4.03,
then that employee  shall not earn,  and shall not otherwise be entitled to, any
bonus  under the Plan for that  fiscal  year.  In no event  shall  any  employee
receive an  allocation  under  Section  4.03 for a fiscal year if that  employee
ceases to be employed by either the Company or one or more of its  participating
subsidiary  corporations for any reason,  other than retirement after the age of
65,  permanent  disability or death, on or before the date the allocation of the
bonus pool for that fiscal year is made under section 4.03.  Notwithstanding the
foregoing,  if an  employee  is  employed  during part of the fiscal year by the
Company or any other participating subsidiary in the Plan and for all or part of
the remainder of that fiscal year by a subsidiary  that is not covered under the
Plan, then any bonus to which that employee would otherwise be entitled for such
fiscal year had he/she  continued in the employ of the Company or  participating
subsidiary  shall be reduced by the  proportion of such fiscal year during which
the employee was employed by the non-participating subsidiary.

                  4.02 The Committee shall calculate the aggregate bonus pool to
be paid under the Plan for each fiscal year.  The specific  percentage in effect
for the fiscal year shall be determined in accordance  with the Company's  level
of success in achieving the budgeted  operating income specified for that fiscal
year in the  annual  Financial  Plan  ("Budgeted  Operating  Income")  which  is
approved by the Board and ratified for purposes of the Plan by the Committee not
later than 90 days after the start of the fiscal year, as follows:

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                              X = The percentage of the Operating  Income of the
         Company and its  subsidiaries  covered by the Plan that  comprises  the
         bonus pool.

                              Y = Actual  Operating  Income for the fiscal  year
         divided by Budgeted Operating Income.

                              If Y is 0.6667 or greater, then X = 9(Y)-4

                              If Y is less than 0.6667, then X = 3Y

                              No amount shall be paid if Y is zero (0) or less.

                              The maximum  value for X shall be limited to seven
percent (7%), and in no event shall X exceed eight percent (8%) of the Company's
Consolidated Operating Income.

                              For purposes of this  Section 4.02 bonus  formula,
the following definitions shall be in effect:

                              "Operating  Income" means the Company's  operating
         income  for  the  fiscal  year  attributable  to the  Company  and  the
         participating subsidiaries for that year.

                              "Consolidated    Operating   Income"   means   the
         Company's   consolidated   operating   income  for  the   fiscal   year
         attributable to the Company and all its subsidiaries.

                              In each case, the calculations of Operating Income
and Consolidated Operating Income shall be in accordance with generally accepted
accounting  principles,  adjusted  to exclude  the  following:  (i) any  amounts
accrued by the Company or its subsidiaries pursuant to Management Bonus Plans or
Cash Profit  Sharing  Plans and related  employer  payroll taxes for such fiscal
year, (ii) any Discretionary or Matching  Contributions  made to the Savings and
Deferred  Profit-Sharing Plan or to the Non-Qualified Deferred Compensation Plan
for such fiscal year,  (iii) all items of gain,  loss or expense for such fiscal
year  determined  to be  extraordinary  or  unusual in nature or  infrequent  in
occurrence,  or  related to the  disposal  of a segment  of a  business,  all as
determined in accordance with the standards established by Opinion No. 30 of the
Accounting  Principles  Board (APB No. 30),  (iv) any  adjustments  to earnings,
gain,  loss or expense  attributable  to a change in  accounting  principles  or
standards,  (v) all items of gain,  loss or expense for such fiscal year related
to  restructuring  charges of subsidiaries  whose operations are not included in
Operating  Income for such fiscal year,  (vi) all items of gain, loss or expense
for such 

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fiscal year related to discontinued operations which do not qualify as a segment
of a  business  as  defined  under  APB No.  30 and  (vii)  any  profit  or loss
attributable  to the business  operations of any entity  acquired by the Company
during such fiscal year.  Operating  Income shall not be adjusted for a minority
interest holder's share of a consolidated subsidiary's operating income or loss.

                  4.03  The  aggregate  bonus  pool  calculated  in  the  manner
provided in Section  4.02 shall be  allocated  among the  eligible  employees in
accordance with this Section 4.03.

                                    A.      Each  of  the  Company's   executive
officers  (salary  grades E11 and above)  will be assigned an index which is the
product of his or her base  salary,  measured as of the close of the fiscal year
for which the bonus allocation is made,  times a multiplier.  The multiplier for
the President and Chief Executive  Officer and the Chairman of the Board will be
two  (2).  For  each  Senior  Vice  President  (E12),  the  multiplier  will  be
one-point-five  (1.5),  and for every other Vice President  (E11) the multiplier
will be one (1).

                                    B.      Bonuses  will  be  awarded  to  each
executive officer by multiplying the aggregate bonus pool for the fiscal year by
a fraction the numerator of which will be the individual officer's index and the
denominator of which will be the sum of the indices for all executive officers.

                                    C.      The  Committee   may,  in  its  sole
judgment  and  discretion,  reduce  the  bonus  allocation  to any or all of the
executive officers.

                                    D.      The sum of all  amounts  not paid to
executive  officers  pursuant to Section  4.03C shall serve as a separate  bonus
pool for the  fiscal  year which may be  allocated  in whole or in part to other
officers  and  exempt  employees  grade  E06 and  above.  One or more  executive
officers  of the  Company  may  make  recommendations  to the  Chairman  and the
President with respect to the  non-executive-officer  employees who should share
in such bonus pool and the  portion  of such pool to be  allocated  to each such
individual. The Chairman and the President shall review such recommendations and
shall, in their  discretion,  submit one or more of such  recommendations  (with
such adjustments as they deem  appropriate) to the Committee for  consideration.
On the basis of such  recommendations,  the  Committee  shall select one or more
such  non-executive-officer  employees to share in such bonus pool and determine
the  amount  of such  pool to be  allocated  to each  selected  individual.  The
determinations of the Committee shall be final.

                                    E.      The bonus award made under this Plan
to any participant for any fiscal year shall not exceed $5 million.

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                  4.04  Following   completion  of  the  bonus  calculation  and
allocation  referenced  above,  the  Committee  shall  issue  a  written  report
containing the final calculation and allocation.

       V.         PAYMENT OF BONUS AWARDS

                  5.01 The  individual  bonus award  allocated to each  employee
pursuant to Section 4.03 shall be paid to such employee  within thirty (30) days
after  completion of the annual audit of the Company's  financial  statements by
its independent auditors.

      VI.         GENERAL PROVISIONS

                  6.01 The Plan shall become effective when adopted by the Board
and the  Company's  stockholders.  The Board may at any time  amend,  suspend or
terminate the Plan,  provided such action is effected by written  resolution and
does  not  adversely  affect  rights  and  interests  of  Plan  participants  to
individual  bonuses  allocated to them prior to such  amendment,  suspension  or
termination.  All  material  amendments  to the Plan shall  require  stockholder
approval.

                  6.02 On January 22,  1997,  the Board  adopted an amendment to
the Plan that changed the bonus  formula  under  Section 4.02  effective for all
fiscal years  following the 1996 fiscal year ended  December 27, 1996 (the "1997
Amendment").  The 1997 Amendment is subject to stockholder  approval at the 1997
Annual Meeting. If the stockholders do not approve the 1997 Amendment,  then the
bonus  formula  in  effect  under  Section  4.02  immediately  prior to the 1997
Amendment shall  automatically be reinstated,  and the bonus pool shall continue
to be calculated in accordance with the reinstated formula.

                  6.03 No  amounts  awarded  or  accrued  under  this Plan shall
actually be funded,  set aside or  otherwise  segregated  prior to payment.  The
obligation  to pay the  bonuses  awarded  hereunder  shall  at all  times  be an
un-funded and unsecured obligation of the Company.  Plan participants shall have
the status of general  creditors and shall look solely to the general  assets of
the Company for the payment of their bonus awards.

                  6.04 No Plan  participant  shall  have the right to  alienate,
pledge or encumber  his/her  interest in this Plan,  and such interest shall not
(to the  extent  permitted  by law) be  subject  in any way to the claims of the
employee's creditors or to attachment, execution or other process of law.

                  6.05  Neither  the action of the Company in  establishing  the
Plan, nor any action taken under the Plan by the Committee, nor any provision of
the Plan, nor  shareholder  approval of the Plan itself shall be construed so as
to grant any  person 

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the right to remain in the  employ of the  Company or its  subsidiaries  for any
period of specific duration.  Rather,  each employee will be employed "at-will,"
which  means  that  either  such  employee  or the  Company  may  terminate  the
employment relationship at any time for any reason, with or without cause.


                  6.06  This is the  full and  complete  agreement  between  the
eligible employees and the Company on the terms described herein.



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