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                                                                     EXHIBIT 4.9

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                              LSI Logic Corporation

                                       and

             State Street Bank and Trust Company of California, N.A.
                                     Trustee


                          Supplemental Trust Indenture

                          Dated as of February 15, 2000

                           Supplementing that certain

                             Subordinated Indenture

                          Dated as of February 15, 2000


                    Authorizing the Issuance and Delivery of

                          Subordinated Debt Securities

                   4% Convertible Subordinated Notes due 2005


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<TABLE>
<CAPTION>
                                TABLE OF CONTENTS
                                                                                              PAGE
                                                                                              ----
<S>                                                                                           <C>
ARTICLE ONE ISSUANCE OF NOTES....................................................................2

        Section 101   Issuance of Notes; Principal Amount; Maturity..............................2
        Section 102   Interest on the Notes; Payment of Interest.................................2

ARTICLE TWO CERTAIN DEFINITIONS..................................................................3

        Section 201   Certain Definitions........................................................3

ARTICLE THREE CERTAIN COVENANTS..................................................................4

        Section 301   Registration and Listing...................................................4

ARTICLE FOUR REDEMPTION OF NOTES.................................................................4

        Section 401   Right of Redemption........................................................4
        Section 402   Conversion Arrangement on Call for Redemption..............................5

ARTICLE FIVE CONVERSION OF NOTES.................................................................5

        Section 501   Conversion Privilege and Conversion Price..................................5
        Section 502   Adjustment of Conversion Price.............................................6

ARTICLE SIX REDEMPTION AT OPTION OF HOLDERS UPON A FUNDAMENTAL CHANGE...........................14

        Section 601   Purchase of Securities at Option of the Holder Upon Fundamental
                      Change ...................................................................14
        Section 602   Compliance With Securities Laws Upon Purchase of Notes....................15
        Section 603   Successive Consolidations, Mergers, Etc...................................15

ARTICLE SEVEN MISCELLANEOUS.....................................................................16

        Section 701   Consent of Holders Required...............................................16
        Section 702   Applicability of Certain Indenture Provisions.............................16
        Section 703   Reference to and Effect on the Indenture..................................16
        Section 704   Supplemental Indenture May be Executed In Counterparts....................17
        Section 705   Effect of Headings........................................................17
        Section 706   Separability..............................................................17
</TABLE>



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        This Supplemental Trust Indenture, dated as of February 15, 2000 (the
"SUPPLEMENTAL INDENTURE"), between LSI Logic Corporation, a corporation duly
organized and existing under the laws of the State of Delaware (the "COMPANY"),
and State Street Bank and Trust Company of California, N.A., a national banking
association organized and existing under the laws of the United States of
America, as Trustee (the "TRUSTEE"), supplementing that certain Subordinated
Indenture, dated as of February 15, 2000, between the Company and the Trustee
(the "INDENTURE").

                                    Recitals

        A. The Company has duly authorized the execution and delivery of the
Indenture heretofore executed and delivered to provide for the issuance from
time to time of its unsecured debentures, notes, or other evidences of
indebtedness to be issued in one or more series as provided for in the Indenture
heretofore executed and delivered.

        B. The Indenture heretofore executed and delivered provides that the
Securities of each series shall be in substantially the form set forth in the
Indenture heretofore executed and delivered, or in such other form as may be
established by or pursuant to a Board Resolution or in one or more supplemental
indentures thereto, in each case with such appropriate insertions, omissions,
substitutions, and other variations as are required or permitted by the
Indenture, and may have such letters, numbers, or other marks of identification
and such legends or endorsements placed thereon as may be required to comply
with the rules of any securities exchange or as may, consistently herewith, be
determined to be required by the officers executing such securities, as
evidenced by their execution thereof.

        C. The Company desires to create a series of Securities denominated "4%
Convertible Subordinated Notes due 2005" pursuant to the terms of this
Supplemental Indenture and substantially in the form set forth below, in each
case with such appropriate insertions, omissions, substitutions, and other
variations as are required or permitted by the Indenture heretofore executed and
delivered and this Supplemental Indenture, and with such letters, numbers, or
other marks of identification and such legends or endorsements placed thereon as
may be required to comply with the rules of any securities exchange or as may,
consistently herewith, be determined by the officers executing such Securities,
as evidenced by their execution of such Securities.



<PAGE>   4

                                   ARTICLE ONE

                                ISSUANCE OF NOTES

Section 101 Issuance of Notes; Principal Amount; Maturity.

        (a) There is hereby authorized a series of Securities designated the 4%
Convertible Subordinated Notes due 2005 (the "NOTES"). The Notes shall mature on
February 15, 2005, which shall be the Stated Maturity of the Notes.

        (b) On February 18, 2000, the Company shall issue and deliver to the
Trustee, and the Trustee shall authenticate, Notes in an aggregate principal
amount not to exceed $500,000,000 (or $575,000,000 if the over-allotment option
set forth in Section 2 of the Underwriting Agreement date February 15, 2000 (as
amended from time to time by the parties thereto) by and between the Company and
the Underwriter is exercised in full), substantially in the form set forth in
Annex 1, in each case with such appropriate insertions, omissions, substitutions
and other variations as are required or permitted by the Indenture and this
Supplemental Indenture, and with such letters, numbers, or other marks of
identification and such legends or endorsements placed thereon as may be
required to comply with the rules of any Securities exchange or as may,
consistently herewith, be determined by the officers executing such Notes, as
evidenced by their execution of such Notes.

Section 102 Interest on the Notes; Payment of Interest.

        (a) The Notes shall bear interest at the rate of 4% per annum from
February 18, 2000 and to and including February 15, 2005. Interest will be
computed on the basis of a 360-day year comprised of twelve 30-day months.

        (b) The interest so payable, and punctually paid or duly provided for,
on any Interest Payment Date shall be paid to the Person in whose name a Note is
registered at the close of business on the Regular Record Date for such
interest, which shall be the February 15 or August 15 (whether or not a Business
Day), as the case may be, next preceding such Interest Payment Date.

        (c) Payment of the principal of (and premium, if any) and any interest
on the Notes shall be made at the office or agency of the Company maintained for
that purpose in the Borough of Manhattan, The City of New York (which shall
initially be State Street Bank and Trust Company, N.A., an affiliate of the
Trustee, as agent of the Trustee) or at the Corporate Trust Office of the
Trustee in such coin or currency of the United States of America as at the time
of payment is legal tender for payment of public and private debts; provided,
however, that at the option of the Company payment of interest may be made (i)
by check mailed to the address of the Person entitled thereto as such address
appears in the Security Register; provided that a Holder with an aggregate
principal amount in excess of $10,000,000 will, at the written election of such
Holder, filed on or before the relevant Record Date with the Trustee, be paid by
wire transfer in immediately available funds at the election of such Holder, or
(ii) by transfer to an account maintained by such Holder located in the United
States.



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<PAGE>   5

        The Company hereby initially designates the Trustee as Paying Agent,
Security Registrar, Custodian and conversion agent, and each of the Corporate
Trust Office of the Trustee and the office of the Trustee in the Borough of
Manhattan, The City of New York (which shall initially be State Street Bank and
Trust Company, N.A., an affiliate of the Trustee, as agent of the Trustee
located at 61 Broadway, 15th floor, New York, New York, 10006, Attn: Corporate
Trust Administration (LSI Logic Corporation 4% Convertible Subordinated Notes
due 2005)), one such office or agency of the Company for each of the aforesaid
purposes.


                                  ARTICLE TWO
                              CERTAIN DEFINITIONS

Section 201 Certain Definitions.

        The terms defined in this Section 201 (except as herein otherwise
expressly provided or unless the context of this Supplemental Indenture
otherwise requires) for all purposes of this Supplemental Indenture and of any
indenture supplemental hereto have the respective meanings specified in this
Section 201. All other terms used in this Supplemental Indenture that are
defined in the Indenture or the Trust Indenture Act, either directly or by
reference therein (except as herein otherwise expressly provided or unless the
context of this Supplemental Indenture otherwise requires), have the respective
meanings assigned to such terms in the Indenture or the Trust Indenture Act, as
the case may be, as in force at the date of this Supplemental Indenture as
originally executed.

        "CAPITAL STOCK" or "CAPITAL STOCK" of any person means any and all
shares, interests, partnership interests, participations, rights or other
equivalents (however designated) of such person's equity interest (however
designated).

        "INTEREST PAYMENT DATES" with respect to the Notes shall be February 15
and August 15.

        "PRINCIPAL AMOUNT" of a Security means the principal amount as set forth
on the face of the Security.

        "REGULAR RECORD DATES" with respect to the Notes shall be February 1 and
August 1.

        "VOTING STOCK" means any class or classes of Capital Stock pursuant to
which the holders thereof under ordinary circumstances have the power to vote in
the election of the board of directors, managers or trustees of any Person (or
other persons performing similar functions), irrespective of whether or not, at
the time, Capital Stock of any other class or classes shall have, or might have,
voting power by reason of the happening of any contingency.

        The definitions of other terms are specified in Articles Five and Six.



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                                  ARTICLE THREE
                                CERTAIN COVENANTS

        The following covenant shall be applicable to the Company for so long as
any of the Notes are outstanding.

Section 301 Registration and Listing.

        The Company (i) will effect all registrations with, and obtain all
approvals by, all governmental authorities that may be necessary under any
United States Federal or state law (including the Securities Act, the Exchange
Act and state securities and Blue Sky laws) before the shares of Common Stock
issuable upon conversion of Notes may be lawfully issued and delivered, and
thereafter publicly traded, and qualified or listed as contemplated by clause
(ii); and (ii) will list the shares of Common Stock required to be issued and
delivered upon conversion of the Notes prior to such issuance or delivery on the
New York Stock Exchange or such other exchange or automated quotation as the
Common Stock is then listed at such date of conversion. The provisions of
Section 1008 of the Indenture shall not apply to this Section 301.


                                  ARTICLE FOUR
                               REDEMPTION OF NOTES

Section 401 Right of Redemption.

        The Notes will not be subject to redemption prior to February 20, 2003
and will be redeemable on and after such date at the option of the Company, in
whole or in part, upon not less than 30 days' notice to the Holders, at the
Redemption Prices (expressed as a percentage of principal amount) set forth
below.

        The Redemption Price (expressed as a percentage of principal amount) is
as follows:

<TABLE>
<CAPTION>
        YEAR                                                                   REDEMPTION PRICE
        ----                                                                   ----------------
<S>                                                                            <C>
        Beginning on February 20, 2003 and ending on February 14, 2004              101.6%
        Beginning on February 15, 2004 and ending on February 14, 2005              100.8%
</TABLE>

and 100% at February 15, 2005, in each case together with accrued and unpaid
interest to, but excluding, the Redemption Date; provided, however, that
interest installments whose Stated Maturity is on such Redemption Date will be
payable to the Holders of such Notes, or one or more Predecessor Securities, of
record at the close of business on the relevant Record Dates referred to on the
face hereof, all as provided in the Indenture.



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<PAGE>   7

        The Notes are not subject to redemption through operation of any sinking
fund.

Section 402 Conversion Arrangement on Call for Redemption.

        In connection with any redemption of Notes, the Company may arrange for
the purchase and conversion of any Notes by an agreement with one or more
investment bankers or other purchasers to purchase such Notes by paying to the
Trustee in trust for the Holders, on or before the date fixed for redemption, an
amount not less than the applicable Redemption Price, together with interest
accrued to (but excluding) the date fixed for redemption, of such Notes.
Notwithstanding anything to the contrary contained herein, the obligation of the
Company to pay the Redemption Price of such Notes, together with unpaid interest
accrued to (but excluding) the Redemption Date, shall be deemed to be satisfied
and discharged to the extent such amount is so paid by such purchasers. If such
an agreement is entered into, a copy of which will be filed with the Trustee
prior to the Redemption Date, any Notes not duly surrendered for conversion by
the Holders thereof may, at the option of the Company, be deemed, to the fullest
extent permitted by law, acquired by such purchasers from such Holders and
(notwithstanding anything to the contrary contained herein) surrendered by such
purchasers for conversion, all as of immediately prior to the close of business
on the Redemption Date (and the right to convert any such Notes shall be
extended through such time), subject to payment of the above amount as
aforesaid. At the direction of the Company, the Trustee shall hold and dispose
of any such amount paid to it in the same manner as it would monies deposited
with it by the Company for the redemption of Notes. Without the Trustee's prior
written consent, no arrangement between the Company and such purchasers for the
purchase and conversion of any Notes shall increase or otherwise affect any of
the powers, duties, responsibilities or obligations of the Trustee as set forth
in the Indenture, and the Company agrees to indemnify the Trustee from, and hold
it harmless against, any loss, liability or expense arising out of or in
connection with any such arrangement for the purchase and conversion of any
Notes between the Company and such purchasers to which the Trustee has not
consented in writing, including the costs and expenses, including reasonable
legal fees, incurred by the Trustee in the defense of any claim or liability
arising out of or in connection with the exercise or performance of any of its
powers, duties, responsibilities or obligations under the Indenture.


                                  ARTICLE FIVE
                               CONVERSION OF NOTES

Section 501 Conversion Privilege and Conversion Price

        Subject to and upon compliance with the provisions of this Article, at
the option of the Holder thereof, any Note may be converted into fully paid and
nonassessable shares of Common Stock of the Company at the Conversion Price,
determined as hereinafter provided, in effect at the time of conversion. Such
conversion right shall commence upon issuance of the Notes and expire at the
close of business on the Business Day next preceding the Stated Maturity of the
Notes, subject, in the case of the conversion of any Global Security, to any
applicable book-entry procedures of the Depositary therefor. In case a Note is
called for redemption at the election of the Company or a Holder is exercising
its option to require redemption of a Note upon a Fundamental Change, such




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conversion right in respect of the Note shall expire at the close of business on
the Business Day next preceding the Redemption Date or the Repurchase Date (as
defined in Article Six) as the case may be, unless the Company defaults in
making the payment due upon redemption or repurchase, as the case may be (in
each case subject as aforesaid to any applicable book entry procedures). A Note
in respect of which a Holder is exercising its option to require redemption upon
a Fundamental Change may be converted only if such Holder withdraws its election
to exercise its option in accordance with Article Six of this Supplemental
Indenture.

        The initial Conversion Price of the Notes is $140.569 per share of
Common Stock. The initial Conversion Price will be adjusted to $70.2845
effective at the opening of business on February 17, 2000, to account for the
distribution by the Company at the close of business on February 16, 2000 of a
stock dividend of one share of Common Stock for each share of Common Stock
outstanding. The Conversion Price shall be further adjusted in certain instances
as provided in this Article Five.

Section 502 Adjustment of Conversion Price

        The Conversion Price shall be adjusted from time to time by the Company
as follows:

        (a) In case the Company shall hereafter pay a dividend or make a
distribution to all holders of the outstanding Common Stock in shares of Common
Stock, the Conversion Price in effect at the opening of business on the date
next following the date fixed for the determination of stockholders entitled to
receive such dividend or other distribution shall be reduced by multiplying such
Conversion Price by a fraction the numerator of which shall be the number of
shares of Common Stock outstanding at the close of business on the date fixed
for such determination and the denominator shall be the sum of such number of
shares and the total number of shares constituting such dividend or other
distribution, such reduction to become effective immediately after the opening
of business on the day following the date fixed for such determination. The
Company will not pay any dividend or make any distribution on shares of Common
Stock held in the treasury of the Company. If any dividend or distribution of
the type described in this subsection (a) is declared but not so paid or made,
the Conversion Price shall again be adjusted to the Conversion Price that would
then be in effect if such dividend or distribution had not been declared.

        (b) In case the Company shall issue rights or warrants to all holders of
its outstanding shares of Common Stock entitling them (for a period expiring
within forty-five (45) days after the date fixed for determination of
stockholders entitled to receive such rights or warrants) to subscribe for or
purchase shares of Common Stock at a price per share less than the Current
Market Price (as defined below) on the date fixed for determination of
stockholders entitled to receive such rights or warrants, the Conversion Price
shall be adjusted so that the same shall equal the price determined by
multiplying the Conversion Price in effect immediately prior to the date fixed
for determination of stockholders entitled to receive such rights or warrants by
a fraction of which the numerator shall be the number of shares of Common Stock
outstanding at the close of business on the date fixed for determination of
stockholders entitled to receive such rights and warrants plus the number of
shares which the aggregate offering price of the total number of shares so
offered would purchase at such Current Market Price, and of which the
denominator shall be the number of shares of Common




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<PAGE>   9

Stock outstanding on the date fixed for determination of stockholders entitled
to receive such rights and warrants plus the total number of additional shares
of Common Stock offered for subscription or purchase. Such adjustment shall be
successively made whenever any such rights and warrants are issued, and shall
become effective immediately after the opening of business on the day next
following the date fixed for determination of stockholders entitled to receive
such rights or warrants. To the extent that shares of Common Stock are not
delivered after the expiration of such rights or warrants, the Conversion Price
shall be readjusted to the Conversion Price which would then be in effect had
the adjustments made upon the issuance of such rights or warrants been made on
the basis of delivery of only the number of shares of Common Stock actually
delivered. In the event that such rights or warrants are not so issued, the
Conversion Price shall again be adjusted to be the Conversion Price which would
then be in effect if such date fixed for the determination of stockholders
entitled to receive such rights or warrants had not been fixed. In determining
whether any rights or warrants entitle the holders to subscribe for or purchase
shares of Common Stock at less than such Current Market Price, and in
determining the aggregate offering price of such shares of Common Stock, there
shall be taken into account any consideration received by the Company for such
rights or warrants, the value of such consideration, if other than cash, to be
determined by the Board of Directors (whose determination shall be conclusive
and described in a resolution of the Board of Directors).

        (c) In case outstanding shares of Common Stock shall be subdivided into
a greater number of shares of Common Stock, the Conversion Price in effect at
the opening of business on the day next following the day upon which such
subdivision becomes effective shall be proportionately reduced, and conversely,
in case outstanding shares of Common Stock shall be combined into a smaller
number of shares of Common Stock, the Conversion Price in effect at the opening
of business on the day next following the day upon which such combination
becomes effective shall be proportionately increased, such reduction or
increase, as the case may be, to become effective immediately after the opening
of business on the day next following the day upon which such subdivision or
combination becomes effective.

        (d) In case the Company shall, by dividend or otherwise, distribute to
all holders of its Common Stock shares of any class of capital stock of the
Company (other than any dividends or distributions to which subsection (a) of
this Section 502 applies) or evidences of its indebtedness or assets (including
securities, but excluding any rights or warrants referred to in subsection (b)
of this Section 502, and excluding any dividend or distribution (x) paid
exclusively in cash or (y) referred to in subsection (a) of this Section 502
(any of the foregoing hereinafter in this subsection (d) called the "SUBJECT
SECURITIES")), then, in each such case (unless the Company elects to reserve
such Subject Securities for distribution to the Holders upon the conversion of
the Notes so that any such Holder converting Notes will receive upon such
conversion, in addition to the shares of Common Stock to which such Holder is
entitled, the amount and kind of such Subject Securities which such Holder would
have received if such Holder had converted its Notes into Common Stock
immediately prior to the Record Date (as defined in subsection (h) of this
Section 502) for such distribution of the Subject Securities)), the Conversion
Price shall be reduced so that the same shall be equal to the price determined
by multiplying the Conversion Price in effect on the Record Date with respect to
such distribution by a fraction of which the numerator shall be the Current
Market Price per share of




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<PAGE>   10

the Common Stock on such Record Date less the fair market value (as determined
by the Board of Directors, whose determination shall be conclusive, and
described in a resolution of the Board if Directors) on such Record Date of the
portion of the Subject Securities so distributed applicable to one share of
Common Stock and the denominator shall be the Current Market Price per share of
the Common Stock on such Record Date, such reduction to become effective
immediately prior to the opening of business on the day next following such
Record Date; provided, however, that in the event the then fair market value (as
so determined) of the portion of the Subject Securities so distributed
applicable to one share of Common Stock is equal to or greater than the Current
Market Price per share of the Common Stock on such Record Date, in lieu of the
foregoing adjustment, adequate provision shall be made so that each Holder shall
have the right to receive upon conversion the amount of Subject Securities such
Holder would have received had such Holder converted each Note on such Record
Date. In the event that such dividend or distribution is not so paid or made,
the Conversion Price shall again be adjusted to be the Conversion Price which
would then be in effect if such dividend or distribution had not been declared.
If the Board of Directors determines the fair market value of any distribution
for purposes of this subsection (d) by reference to the actual or when issued
trading market for any securities, it must in doing so consider the prices in
such market over the same period used in computing the Current Market Price of
the Common Stock.

        Under the provisions of the Company's Preferred Shares Rights Plan (the
"RIGHTS PLAN"), upon conversion of the Notes into Common Stock, to the extent
that the Rights Plan is still in effect upon such conversion, the Holders of
Notes will receive, in addition to the Common Stock, the rights described
therein (whether or not the rights have separated from the Common Stock at the
time of conversion), subject to the limitations set forth in the Rights Plan.

        Rights or warrants distributed by the Company to all holders of Common
Stock entitling the holders thereof to subscribe for or purchase shares of the
Company's capital stock (either initially or under certain circumstances), which
rights or warrants, until the occurrence of a specified event or events
("TRIGGER EVENT"): (i) are deemed to be transferred with such shares of Common
Stock; (ii) are not exercisable; and (iii) are also issued in respect of future
issuances of Common Stock, shall be deemed not to have been distributed for
purposes of this Section 502 (and no adjustment to the Conversion Price under
this Section 502 will be required) until the occurrence of the earliest Trigger
Event, whereupon such rights and warrants shall be deemed to have been
distributed and an appropriate adjustment (if any is required) to the Conversion
Price shall be made under this subsection (d). If any such right or warrant,
including any such existing rights or warrants distributed prior to the date of
this Supplemental Indenture, are subject to events, upon the occurrence of which
such rights or warrants become exercisable to purchase different securities,
evidences of indebtedness or other assets, then the date of the occurrence of
any and each such event shall be deemed to be the date of distribution and
record date with respect to new rights or warrants with such rights (and a
termination or expiration of the existing rights or warrants without exercise by
any of the holders thereof). In addition, in the event of any distribution (or
deemed distribution) of rights or warrants, or any Trigger Event or other event
(of the type described in the preceding sentence) with respect thereto that was
counted for purposes of calculating a distribution amount for which an
adjustment to the Conversion Price under this Section 502 was made, (1) in the
case of any such rights or warrants which shall all have been redeemed or
repurchased without exercise by any




                                      -8-
<PAGE>   11

holders thereof, the Conversion Price shall be readjusted upon such final
redemption or repurchase to give effect to such distribution or Trigger Event,
as the case may be, as though it were a cash distribution, equal to the per
share redemption or repurchase price received by a holder or holders of Common
Stock with respect to such rights or warrants (assuming such holder had retained
such rights or warrants), made to all holders of Common Stock as of the date of
such redemption or repurchase, and (2) in the case of such rights or warrants
which shall have expired or been terminated without exercise by any holders
thereof, the Conversion Price shall be readjusted as if such rights and warrants
had not been issued.

        For purposes of this subsection (d) and subsections (a) and (b) of this
Section 502, any dividend or distribution to which this subsection (d) is
applicable that also includes shares of Common Stock, or rights or warrants to
subscribe for or purchase shares of Common Stock (or both), shall be deemed
instead to be (1) a dividend or distribution of the evidences of indebtedness,
assets or shares of capital stock other than such shares of Common Stock or
rights or warrants to purchase shares of Common Stock (and any Conversion Price
reduction required by this subsection (d) with respect to such dividend or
distribution shall then be made) immediately followed by (2) a dividend or
distribution of such shares of Common Stock or such rights or warrants (and any
further Conversion Price reduction required by subsections (a) and (b) of this
Section 502 with respect to such dividend or distribution shall then be made),
except (A) the Record Date of such dividend or distribution shall be substituted
as "the date fixed for the determination of stockholders entitled to receive
such dividend or other distribution" and "the date fixed for such determination"
within the meaning of subsections (a) and (b) of this Section 502 and (B) any
shares of Common Stock included in such dividend or distribution shall not be
deemed "outstanding at the close of business on the date fixed for such
determination" within the meaning of subsection (a) of this Section 502.

        (e) In case the Company shall, by dividend or otherwise, distribute to
all holders of its Common Stock cash (excluding (x) any quarterly cash dividend
on the Common Stock to the extent the aggregate cash dividend per share of
Common Stock in any fiscal quarter does not exceed the greater of (A) the amount
per share of Common Stock of the next preceding quarterly cash dividend on the
Common Stock to the extent that such preceding quarterly dividend did not
require any adjustment of the Conversion Price pursuant to this subsection (e)
(as adjusted to reflect subdivisions or combinations of the Common Stock), and
(B) 3.75% of the arithmetic average of the Closing Price (determined as set
forth in subsection (h) of this Section 502) during the ten Trading Days (as
defined in) during the ten Trading Days (as defined in subsection (h) of this
Section 502) immediately prior to the date of declaration of such dividend, and
(y) any dividend or distribution in connection with the liquidation, dissolution
or winding up of the Company, whether voluntary or involuntary), then, in such
case, the Conversion Price shall be reduced so that the same shall equal the
price determined by multiplying the Conversion Price in effect immediately prior
to the close of business on the Record Date for such dividend or distribution,
as the case may be, by a fraction the numerator of which shall be the Current
Market Price of the Common Stock on such Record Date less the amount of cash so
distributed (and not excluded as provided above) applicable to one share of
Common Stock and the denominator shall be such Current Market Price of the
Common Stock, such reduction to be effective immediately prior to the opening of
business on the day next following such Record Date; provided, however, that in
the event the portion of the cash so distributed




                                      -9-
<PAGE>   12

applicable to one share of Common Stock is equal to or greater than the Current
Market Price of the Common Stock on such Record Date, in lieu of the foregoing
adjustment, adequate provision shall be made so that each Holder shall have the
right to receive upon conversion the amount of cash such Holder would have
received had such Holder converted each Note on such Record Date. In the event
that such dividend or distribution is not so paid or made, the Conversion Price
shall again be adjusted to be the Conversion Price which would then be in effect
if such dividend or distribution had not been declared. If any adjustment is
required to be made as set forth in this subsection (e) as a result of a
distribution that is a quarterly dividend, such adjustment shall be based upon
the amount by which such distribution exceeds the amount of the quarterly cash
dividend permitted to be excluded pursuant hereto. If an adjustment is required
to be made as set forth in this subsection (e) above as a result of a
distribution that is not a quarterly dividend, such adjustment shall be based
upon the full amount of the distribution.

        (f) In case a tender or exchange offer made by the Company or any
Subsidiary for all or any portion of the Common Stock shall expire and such
tender or exchange offer (as amended upon the expiration thereof) shall require
the payment to stockholders of consideration per share of Common Stock having a
fair market value (as determined by the Board of Directors, whose determination
shall be conclusive and described in a resolution of the Board of Directors)
that as of the last time (the "EXPIRATION TIME") tenders or exchanges may be
made pursuant to such tender or exchange offer (as it may be amended) exceeds
the Current Market Price of the Common Stock on the Trading Day next succeeding
the Expiration Time, the Conversion Price shall be reduced so that the same
shall equal the price determined by multiplying the Conversion Price in effect
immediately prior to the Expiration Time by a fraction of which the numerator
shall be the number of shares of Common Stock outstanding (including any
tendered or exchanged shares) at the Expiration Time multiplied by the Current
Market Price of the Common Stock on the Trading Day next succeeding the
Expiration Time and the denominator shall be the sum of (x) the fair market
value (determined as aforesaid) of the aggregate consideration payable to
stockholders based on the acceptance (up to any maximum specified in the terms
of the tender or exchange offer) of all shares validly tendered or exchanged and
not withdrawn as of the Expiration Time (the shares deemed so accepted, up to
any such maximum, being referred to as the "PURCHASED SHARES") and (y) the
product of the number of shares of Common Stock outstanding (less any Purchased
Shares) at the Expiration Time and the Current Market Price of the Common Stock
on the Trading Day next succeeding the Expiration Time, such reduction to become
effective immediately prior to the opening of business on the day next following
the Expiration Time. In the event that the Company is obligated to purchase
shares pursuant to any such tender or exchange offer, but the Company is
permanently prevented by applicable law from effecting any such purchases or all
such purchases are rescinded, the Conversion Price shall again be adjusted to be
the Conversion Price which would then be in effect if such tender or exchange
offer had not been made.

        (g) In case of a tender or exchange offer made by a person other than
the Company or any Subsidiary for an amount which increases the offeror's
ownership of Common Stock to more than twenty-five percent (25%) of the Common
Stock outstanding and shall involve the payment by such person of consideration
per share of Common Stock having a fair market value (as determined by the Board
of Directors, whose determination shall be conclusive, and described in a
resolution of the




                                      -10-
<PAGE>   13

Board of Directors) at the last time (the "OFFER EXPIRATION TIME") tenders or
exchanges may be made pursuant to such tender or exchange offer (as it shall
have been amended) that exceeds the Current Market Price of the Common Stock on
the Trading Day next succeeding the Offer Expiration Time, and in which, as of
the Offer Expiration Time the Board of Directors is not recommending rejection
of the offer, the Conversion Price shall be reduced so that the same shall equal
the price determined by multiplying the Conversion Price in effect immediately
prior to the Offer Expiration Time by a fraction of which the numerator shall be
the number of shares of Common Stock outstanding (including any tendered or
exchanged shares) at the Offer Expiration Time multiplied by the Current Market
Price of the Common Stock on the Trading Day next succeeding the Offer
Expiration Time and the denominator shall be the sum of (x) the fair market
value (determined as aforesaid) of the aggregate consideration payable to
stockholders based on the acceptance (up to any maximum specified in the terms
of the tender or exchange offer) of all shares validly tendered or exchanged and
not withdrawn as of the Offer Expiration Time (the shares deemed so accepted, up
to any such maximum, being referred to as the "ACCEPTED PURCHASED SHARES") and
(y) the product of the number of shares of Common Stock outstanding (less any
Accepted Purchased Shares) on the Offer Expiration Time and the Current Market
Price of the Common Stock on the Trading Day next succeeding the Offer
Expiration Time, such reduction to become effective immediately prior to the
opening of business on the day next following the Offer Expiration Time. In the
event that such person is obligated to purchase shares pursuant to any such
tender or exchange offer, but such person is permanently prevented by applicable
law from effecting any such purchases or all such purchases are rescinded, the
Conversion Price shall again be adjusted to be the Conversion Price which would
then be in effect if such tender or exchange offer had not been made.
Notwithstanding the foregoing, the adjustment described in this subsection (g)
shall not be made if, as of the Offer Expiration Time, the offering documents
with respect to such offer disclose a plan or intention to cause the Company to
engage in any transaction described in Article Eight of the Indenture.

        (h) For purposes of this Section 502, the following terms shall have the
meaning indicated:

               (1) "CLOSING PRICE" with respect to any securities on any day
shall mean the closing sale price regular way on such day or, in case no such
sale takes place on such day, the average of the reported closing bid and asked
prices, regular way, in each case as quoted on the Nasdaq National Market, or,
if such security is not listed or admitted to trading on the Nasdaq National
Market, on the principal national security exchange or quotation system on which
such security is quoted or listed or admitted to trading, or, if not quoted or
listed or admitted to trading on any national securities exchange or quotation
system, the average of the closing bid and asked prices of such security on the
over-the-counter market on the day in question as reported by the National
Quotation Bureau Incorporated, or a similar generally accepted reporting
service, or if not so available, in such manner as furnished by any New York
Stock Exchange member firm selected from time to time by the Board of Directors
for that purpose, or a price determined in good faith by the Board of Directors
or, to the extent permitted by applicable law, a duly authorized committee
thereof, whose determination shall be conclusive.




                                      -11-
<PAGE>   14

               (2) "CURRENT MARKET PRICE" shall mean the average of the daily
Closing Prices per share of Common Stock for the ten consecutive Trading Days
immediately prior to the date in question; provided, however, that (1) if the
"ex" date (as hereinafter defined) for any event (other than the issuance or
distribution or Fundamental Change requiring such computation) that requires an
adjustment to the Conversion Price pursuant to subsections (a), (b), (c), (d),
(e), (f) or (g) of this Section 502 occurs during such ten consecutive Trading
Days, the Closing Price for each Trading Day prior to the "ex" date for such
other event shall be adjusted by multiplying such Closing Price by the same
fraction by which the Conversion Price is so required to be adjusted as a result
of such other event, (2) if the "ex" date for any event (other than the
issuance, distribution or Fundamental Change requiring such computation) that
requires an adjustment to the Conversion Price pursuant to subsections (a), (b),
(c), (d), (e), (f) or (g) of this Section 502 occurs on or after the "ex" date
for the issuance or distribution requiring such computation and prior to the day
in question, the Closing Price for each Trading Day on and after the "ex" date
for such other event shall be adjusted by multiplying such Closing Price by the
reciprocal of the fraction by which the Conversion Price is so required to be
adjusted as a result of such other event, and (3) if the "ex" date for the
issuance, distribution or Fundamental Change requiring such computation is prior
to the day in question, after taking into account any adjustment required
pursuant to clause (1) or (2) of this proviso, the Closing Price for each
Trading Day on or after such "ex" date shall be adjusted by adding thereto the
amount of any cash and the fair market value (as determined by the Board of
Directors or, to the extent permitted by applicable law, a duly authorized
committee thereof in a manner consistent with any determination of such value
for purposes of subsection (d), (f) or (g) of this Section 502, whose
determination shall be conclusive and described in a resolution of the Board of
Directors or such duly authorized committee thereof, as the case may be) of the
evidences of indebtedness, shares of capital stock or assets being distributed
applicable to one share of Common Stock as of the close of business on the day
before such "ex" date. For purposes of any computation under subsections (f) or
(g) of this Section 502, the Current Market Price of the Common Stock on any
date shall be deemed to be the average of the daily Closing Prices per share of
Common Stock for such day and the next two succeeding Trading Days; provided,
however, that if the "ex" date for any event (other than the tender or exchange
offer requiring such computation) that requires an adjustment to the Conversion
Price pursuant to subsections (a), (b), (c), (d), (e), (f) or (g) of this
Section 502 occurs on or after the Expiration Time or Offer Expiration Time, as
the case may be, for the tender or exchange offer requiring such computation and
prior to the day in question, the Closing Price for each Trading Day on and
after the "ex" date for such other event shall be adjusted by multiplying such
Closing Price by the reciprocal of the fraction by which the Conversion Price is
so required to be adjusted as a result of such other event. For purposes of this
paragraph, the term "ex" date, (1) when used with respect to any issuance or
distribution, means the first date on which the Common Stock trades regular way
on the relevant exchange or in the relevant market from which the Closing Price
was obtained without the right to receive such issuance or distribution, (2)
when used with respect to any subdivision or combination of shares of Common
Stock, means the first date on which the Common Stock trades regular way on such
exchange or in such market after the time at which such subdivision or
combination becomes effective, and (3) when used with respect to any tender or
exchange offer means the first date on which the Common Stock trades regular way
on such exchange or in such market after the Offer Expiration Time of such
offer.




                                      -12-
<PAGE>   15

                  (3) "FAIR MARKET VALUE" shall mean the amount which a willing
buyer would pay a willing seller in an arm's length transaction.

                  (4) "RECORD DATE" shall mean, with respect to any dividend,
distribution or other transaction or event in which the holders of Common Stock
have the right to receive any cash, securities or other property or in which the
Common Stock (or other applicable security) is exchanged for or converted into
any combination of cash, securities or other property, the date fixed for
determination of stockholders entitled to receive such cash, securities or other
property (whether such date is fixed by the Board of Directors or by statute,
contract or otherwise).

                  (5) "TRADING DAY" shall mean (x) if the applicable security is
listed or admitted for trading on the New York Stock Exchange or another
national security exchange, a day on which the New York Stock Exchange or
another national security exchange is open for business or (y) if the applicable
security is quoted on the Nasdaq National Market, a day on which trades may be
made on thereon or (z) if the applicable security is not so listed, admitted for
trading or quoted, any day other than a Saturday or Sunday or a day on which
banking institutions in the State of New York are authorized or obligated by law
or executive order to close.

        (i) The Company may make such reductions in the Conversion Price, in
addition to those required by subsections (a), (b), (c), (d), (e), (f) or (g) of
this Section 502 as the Board of Directors considers to be advisable to avoid or
diminish any income tax to holders of Common Stock or rights to purchase Common
Stock resulting from any dividend or distribution of stock (or rights to acquire
stock) or from any event treated as such for income tax purposes.

        To the extent permitted by applicable law, the Company from time to time
may reduce the Conversion Price by any amount for any period of time if the
period is at least twenty (20) days, the reduction is irrevocable during the
period and the Board of Directors shall have made a determination that such
reduction would be in the best interests of the Company, which determination
shall be conclusive. Whenever the Conversion Price is reduced pursuant to the
preceding sentence, the Company shall mail to holders of record of the Notes a
notice of the reduction at least fifteen (15) days prior to the date the reduced
Conversion Price takes effect, and such notice shall state the reduced
Conversion Price and the period during which it will be in effect.

        (j) No adjustment in the Conversion Price shall be required unless such
adjustment would require an increase or decrease of at least one percent (1%) in
such price; provided, however, that any adjustments which by reason of this
subsection (j) are not required to be made shall be carried forward and taken
into account in any subsequent adjustment. All calculations under this Article
Five shall be made by the Company and shall be made to the nearest cent or to
the nearest one-hundredth (1/100) of a share, as the case may be. No adjustment
need be made for rights to purchase Common Stock pursuant to a Company plan for
reinvestment of dividends or interest. To the extent the Notes become
convertible into cash, assets, property or securities (other than capital stock
of the Company), no adjustment need be made thereafter as to the cash, assets,
property or such securities. Interest will not accrue on the cash.




                                      -13-
<PAGE>   16

        (k) In any case in which this Section 502 provides that an adjustment
shall become effective immediately after a record date for an event, the Company
may defer until the occurrence of such event (i) issuing to the Holder of any
Note converted after such record date and before the occurrence of such event
the additional shares of Common Stock issuable upon such conversion by reason of
the adjustment required by such event over and above the Common Stock issuable
upon such conversion before giving effect to such adjustment and (ii) paying to
such Holder any amount in cash in lieu of any fraction pursuant to the
Indenture.

         For purposes of this Section 502, the number of shares of Common Stock
at any time outstanding shall not include shares held in the treasury of the
Company but shall include shares issuable in respect of scrip certificates
issued in lieu of fractions of shares of Common Stock. The Company will not pay
any dividend or make any distribution on shares of Common Stock held in the
treasury of the Company.


                                   ARTICLE SIX
            REDEMPTION AT OPTION OF HOLDERS UPON A FUNDAMENTAL CHANGE

Section 601 Purchase of Securities at Option of the Holder Upon Fundamental
Change.

        (a) If there shall occur a Fundamental Change at any time prior to the
Stated Maturity of the Notes or the redemption of the Notes, then each Holder of
Notes shall have the right, at such Holder's option, to require the Company to
redeem all of such Holder's Notes, or any portion thereof that is an integral
multiple of $1,000 principal amount, on the date (the "REPURCHASE DATE") that is
thirty (30) days after the date of the Company Notice (as defined in subsection
(b) of this Section 601) of such Fundamental Change (or, if such 30th day is not
a Business Day, the next succeeding Business Day). Such repayment shall be made
at a price equal to 100% of the principal amount to be redeemed. The Company
shall also pay to such Holders accrued but unpaid interest on the redeemed Notes
to, but excluding, the Repurchase Date; provided that, if such Repurchase Date
is February 15 or August 15, then the interest payable on such date shall be
paid to the holders of record of the Notes on the next preceding February 1 or
August 1, respectively.

        The term "FUNDAMENTAL CHANGE" shall mean the occurrence of any
transaction or event in connection with which all or substantially all the
Common Stock shall be exchanged for, be converted into, acquired for, or
constitute solely the right to receive, consideration (whether by means of an
exchange offer, liquidation, tender offer, consolidation, merger, combination,
reclassification, recapitalization or otherwise) which is not all or
substantially all common stock listed (or, upon consummation of or immediately
following such transaction or event, which will be listed) on a United States
national securities exchange or approved for quotation on the Nasdaq National
Market or any similar United States system of automated dissemination of
quotations of securities prices.

        (b) On or before the tenth day after the occurrence of a Fundamental
Change, the Company shall mail or cause to be mailed by first class mail to all
holders of record on the date of the Fundamental Change a notice (the "COMPANY
NOTICE") of the occurrence of such Fundamental




                                      -14-
<PAGE>   17

Change and of the redemption right at the option of the Holders arising as a
result thereof. The Company shall also deliver a copy of the Company Notice to
the Trustee at such time as it is mailed to Holders of Notes.

        Each Company Notice shall specify the circumstances constituting the
Fundamental Change, the Repurchase Date, the latest time (not less than thirty
(30) days after the date of the Company's notice of a Fundamental Change) on the
Repurchase Date by which the Holder must exercise the redemption right (the
"FUNDAMENTAL CHANGE EXPIRATION TIME"), that the Holder shall have the right to
withdraw any Notes surrendered prior to the Fundamental Change Expiration Time,
a description of the procedure which a Holder must follow to exercise such
redemption right and to withdraw any surrendered Notes, the place or places
where the Holder is to surrender such Holder's Notes, and the amount of unpaid
interest accrued on each Note to the Repurchase Date.

        No failure of the Company to give the foregoing notices and no defect
therein shall limit the Holders' redemption rights or affect the validity of the
proceedings for the repurchase of the Notes pursuant to this Section 601.

        (c) For a Note to be so repaid at the option of the Holder, the Company
must receive at the office or agency of the Company maintained for that purpose
or, at the option of such Holder, the Corporate Trust Office, such Note with the
form entitled "Option to Elect Repurchase Upon A Fundamental Change" on the
reverse thereof duly completed, together with such Notes duly endorsed for
transfer, on or before the Fundamental Change Expiration Time. All questions as
to the validity, eligibility (including time of receipt) and acceptance of any
Note for repayment shall be determined by the Company, whose determination shall
be final and binding absent manifest error.

        (d) On or prior to the Repurchase Date, the Company will deposit with
the Trustee or with one or more paying agents (or, if the Company is acting as
its own paying agent, set aside, segregate and hold in trust as provided in
Section 1003 of the Indenture) an amount of money sufficient to repay on the
Repurchase Date all the Notes to be repaid on such date at the appropriate
redemption price, together with accrued but unpaid interest to (but excluding)
the Repurchase Date; provided that if such payment is made on the Repurchase
Date it must be received by the Trustee or paying agent, as the case may be, by
10:00 a.m. New York City time, on such date. Payment for Notes surrendered for
redemption (and not withdrawn) prior to the Fundamental Change Expiration Time
will be made promptly (but in no event more than five (5) Business Days)
following the Repurchase Date by mailing checks for the amount payable to the
Holders of such Notes entitled thereto as they shall appear on the registry
books of the Company.

Section 602 Compliance With Securities Laws Upon Purchase of Notes.

        The Company will comply with the applicable tender offer rules under the
Exchange Act to the extent then applicable in connection with the redemption
rights of the Holders of Notes in the event of a Fundamental Change.

Section 603 Successive Consolidations, Mergers, Etc.


                                      -15-
<PAGE>   18

        In the case of a reclassification, change, consolidation, merger,
combination, sale or conveyance to which Section 801 of the Indenture applies,
in which the Common Stock of the Company is changed or exchanged as a result
into the right to receive stock, securities or other property or assets
(including cash), which includes shares of Common Stock of the Company or
another person that are, or upon issuance will be, traded on a United States
national securities exchange or approved for trading on an established automated
over-the-counter trading market in the United States and such shares constitute
at the time such change or exchange becomes effective in excess of 50% of the
aggregate fair market value of such stock, securities or other property or
assets (including cash) into which the Common Stock of the Company is or is to
be changed or exchanged or (as determined by the Company, which determination
shall be conclusive and binding), then the person formed by such consolidation
or resulting from such merger or which acquires such assets, as the case may be,
shall execute and deliver to the Trustee a supplemental indenture (accompanied
by an Opinion of Counsel that such supplemental indenture complies with the
Trust Indenture Act as in force at the date of execution of such supplemental
indenture) modifying the provisions of this Indenture relating to the right of
Holders of the Notes to cause the Company to repurchase the Notes following a
Fundamental Change, including without limitation the applicable provisions of
this Section 601 and the definitions of Common Stock and Fundamental Change, as
appropriate, as determined in good faith by the Company (which determination
shall be conclusive and binding), to make such provisions apply to such other
person if different from the Company and the common stock issued thereby (in
lieu of the Company and the Common Stock of the Company).


                                  ARTICLE SEVEN
                                  MISCELLANEOUS

Section 701 Consent of Holders Required.

        In addition to those modifications or amendments requiring the consent
of the Holder of each Outstanding Note effected thereby specified in Section 902
of the Indenture, there can be no modification or amendment that would change
the obligation of the Company to redeem any Note upon the happening of a
Fundamental Change in a manner adverse to the Holder of Notes without the
consent of the Holder of each outstanding Note effected thereby.

Section 702 Applicability of Certain Indenture Provisions.

        Each of the defeasance and covenant defeasance provisions of Article
Thirteen of the Indenture shall apply to the Notes; provided, however, that the
Company will not be able to defease the right of the Holders to convert the
Notes pursuant to Article Fourteen of the Indenture.

Section 703 Reference to and Effect on the Indenture.

        This Supplemental Indenture shall be construed as supplemental to the
Indenture and all the terms and conditions of this Supplemental Indenture shall
be deemed to be part of the terms and




                                      -16-
<PAGE>   19

conditions of the Indenture. Except as set forth herein, the Indenture
heretofore executed and delivered is hereby ratified, approved and confirmed.
The provisions of this Supplemental Indenture shall for the purposes of this
series of Securities supersede the provisions of the Indenture heretofore
executed and delivered to the extent the Indenture heretofore executed and
delivered is inconsistent herewith. This Supplemental Indenture is subject to
the provisions of the Trust Indenture Act, and shall, to the extent applicable,
be governed by such provisions.

Section 704 Supplemental Indenture May be Executed In Counterparts.

        This instrument may be executed in any number of counterparts, each of
which shall be an original; but such counterparts shall together constitute but
one and the same instrument.

Section 705 Effect of Headings.

        The Article and Section headings herein are for convenience only and
shall not affect the construction hereof.

Section 706 Separability

        In case any one or more of the provisions contained in this Supplemental
Indenture or in the Notes shall for any reason be held to be invalid, illegal or
unenforceable in any respect, such invalidity, illegality or unenforceability
shall not effect any other provisions of this Supplemental Indenture or of the
Notes, but this Supplemental Indenture and the Notes shall be construed as if
such invalid or illegal or unenforceable provision had never been contained
herein or therein.



                                      -17-
<PAGE>   20

        IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed all as of the day and year first above written.

                                        LSI LOGIC CORPORATION




                                        By: /s/ Wilfred J. Corrigan
                                            ----------------------------------
                                        Name: Wilfred J. Corrigan
                                        Title: Chairman and Chief Executive
                                               Officer





                                        STATE STREET BANK AND TRUST COMPANY OF
                                        CALIFORNIA, N. A., as Trustee




                                        By: /s/ Joni D'Amico
                                            ----------------------------------
                                            Authorized Signatory



<PAGE>   21

                                     Annex 1

                           [Form of Face of Security]

[IF THE SECURITY IS A GLOBAL SECURITY, INSERT -- THIS SECURITY IS A GLOBAL
SECURITY WITHIN THE MEANING OF THE INDENTURE HEREINAFTER REFERRED TO AND IS
REGISTERED IN THE NAME OF A DEPOSITARY OR A NOMINEE THEREOF. THIS SECURITY MAY
NOT BE EXCHANGED IN WHOLE OR IN PART FOR A SECURITY REGISTERED, AND NO TRANSFER
OF THIS SECURITY IN WHOLE OR IN PART MAY BE REGISTERED, IN THE NAME OF ANY
PERSON OTHER THAN SUCH DEPOSITARY OR A NOMINEE THEREOF, EXCEPT IN THE LIMITED
CIRCUMSTANCES DESCRIBED IN THE INDENTURE.]

                              LSI LOGIC CORPORATION

                    4% Convertible Subordinated Note due 2005

No. _________                                                     $_____________

                                                                      CUSIP:

        LSI Logic Corporation, a corporation duly organized and existing under
the laws of Delaware (herein called the "COMPANY," which term includes any
successor Person under the Indenture hereinafter referred to), for value
received, hereby promises to pay to ________________, or registered assigns, the
principal sum of ___________________ Dollars on February 15, 2005 and to pay
interest thereon from February 18, 2000 or from the most recent Interest Payment
Date to which interest has been paid or duly provided for, semi-annually on
February 15 and August 15 in each year, commencing August 15, 2000, at the rate
of 4% per annum, until the principal hereof is paid or made available for
payment. The interest so payable, and punctually paid or duly provided for, on
any Interest Payment Date will, as provided in such Indenture, be paid to the
Person in whose name this Security (or one or more Predecessor Securities) is
registered at the close of business on the Regular Record Date for such
interest, which shall be the February 1 or August 1 (whether or not a Business
Day), as the case may be, next preceding such Interest Payment Date. Any such
interest not so punctually paid or duly provided for will forthwith cease to be
payable to the Holder on such Regular Record Date and may either be paid to the
Person in whose name this Security (or one or more Predecessor Securities) is
registered at the close of business on a Special Record Date for the payment of
such Defaulted Interest to be fixed by the Trustee, notice whereof shall be
given to Holders of Securities of this series not less than 10 days prior to
such Special Record Date, or be paid at any time in any other lawful manner not
inconsistent with the requirements of any securities exchange on which the
Securities of this series may be listed, and upon such notice as may be required
by such exchange, all as more fully provided in said Indenture.

        Payment of the principal of (and premium, if any) and any interest on
this Security will be made at the office or agency of the Company maintained for
such purpose in the Borough of




<PAGE>   22

Manhattan, The City of New York, or at the option of the Holder of this
Security, at the Corporate Trust Office, in such coin or currency of the United
States of America as at the time of payment is legal tender for payment of
public and private debts; provided, however, that at the option of the Company
payment of interest may be made either (i) by check mailed to the address of the
Person entitled thereto as such address shall appear in the Security Register;
provided, further, that a Holder with an aggregate principle amount in excess of
$10,000,000 will, at the written election of the Holder, filed on or before the
relevant Record Date with the Trustee, be paid by wire transfer in immediately
available funds, or (ii) by transfer to an account maintained by such Holder
located in the United States. Interest will be computed on the basis of a
360-day year comprised of twelve 30-day months.

        Reference is hereby made to the further provisions of this Security set
forth on the reverse hereof, which further provisions shall for all purposes
have the same effect as if set forth at this place.

        Unless the certificate of authentication hereon has been executed by the
Trustee referred to on the reverse hereof by manual signature, this Security
shall not be entitled to any benefit under the Indenture or be valid or
obligatory for any purpose.

        IN WITNESS WHEREOF, the Company has caused this instrument to be signed
manually or by facsimile by their duly authorized officers and by its corporate
seal to be affixed or imported hereon.

Dated:    February 18, 2000               LSI LOGIC CORPORATION



                                          By:___________________________________
                                              Title:

Attest:

By:___________________________________
    Title:

        The Trustee's certificates of authentication shall be in substantially
the following form:

        This is one of the Securities of the series designated herein referred
to in the within-mentioned Indenture.

                                          STATE STREET BANK AND TRUST COMPANY OF
                                          CALIFORNIA, N.A.
                                          As Trustee



                                      -20-
<PAGE>   23

                                          By:___________________________________
                                                    Authorized Signatory




                                      -21-
<PAGE>   24

                           FORM OF REVERSE OF SECURITY

        This Security is one of a duly authorized issue of securities of the
Company (herein called the "SECURITIES") issued and to be issued in one or more
series under a Subordinated Indenture, dated as of February 15, 2000 (herein
called the "INDENTURE," which term shall have the meaning assigned to it in such
instrument), between the Company and State Street Bank and Trust Company of
California, N.A., as Trustee (herein called the "TRUSTEE," which term includes
any successor trustee under the Indenture), and reference is hereby made to the
Indenture and all indentures supplemental thereto for a statement of the
respective rights, limitations of rights, duties and immunities thereunder of
the Company, the Trustee, the holders of Senior Indebtedness and the Holders of
the Securities and of the terms upon which the Securities are, and are to be,
authenticated and delivered. This Security is one of the series designated on
the face hereof and is issued pursuant to a Supplemental Trust Indenture
supplementing the Indenture, dated as of February 15, 2000, from the Company to
Trustee relating to the issuance of the "4% Convertible Notes due 2005" of this
series (the "SUPPLEMENTAL INDENTURE").

        The Securities will not be subject to redemption prior to February 20,
2003 and will be redeemable on and after such date at the option of the Company,
in whole or in part, upon not less than 30 days' notice to the Holders, at the
Redemption Prices (expressed as a percentage of principal amount) set forth
below.

        The Redemption Price (expressed as a percentage of principal amount) is
as follows:

<TABLE>
<CAPTION>
                                                                                      REDEMPTION
        YEAR                                                                          PRICE
        ----                                                                          -----
<S>                                                                                   <C>
        Beginning on February 20, 2003 and ending on February 14, 2004                  101.6%
        Beginning on February 15, 2004 and ending on February 14, 2005                  100.8%
</TABLE>

and 100% at February 15, 2005, in each case together with accrued and unpaid
interest to, but excluding, the Redemption Date; provided, however, that
interest installments whose Stated Maturity is on such Redemption Date will be
payable to the Holders of such Securities, or one or more Predecessor
Securities, of record at the close of business on the relevant Record Dates
referred to on the face hereof, all as provided in the Indenture.

        The Securities are not subject to redemption through operation of any
sinking fund.

        In the event of redemption of this Security in part only, a new Security
or Securities of this series and of like tenor for the unredeemed portion hereof
will be issued in the name of the Holder hereof upon the cancellation hereof.

        If a Fundamental Change (as defined in the Supplemental Indenture)
occurs at any time prior to February 15, 2005 or the redemption of the
Securities, the Securities will be redeemable on the



                                      -22-
<PAGE>   25

30th day after notice thereof at the option of the Holder. Such payment shall be
made at a purchase price equal to the principal amount of the Security plus
accrued and unpaid interest to, but excluding, the Repurchase Date (as defined
in the Supplemental Indenture). The Company shall mail to all Holders a notice
of the occurrence of a Fundamental Change and of the redemption right arising as
a result thereof on or before the 10th Business Day after the occurrence of such
Fundamental Change. For a Security to be so repaid at the option of the Holder,
the Company must receive at the office or agency of the Company maintained for
that purpose according to the terms of the Indenture, such Security with the
form entitled "Option to Elect Redemption Upon a Fundamental Change" on the
reverse thereof duly completed, together with such Securities duly endorsed for
transfer, on or before the 30th day after the date of the Company's notice (or
if such 30th day is not a Business Day, the immediately preceding Business Day).

        The indebtedness evidenced by this Security is, to the extent and in the
manner provided in the Indenture, subordinate and subject in right of payment to
the prior payment in full of all Senior Indebtedness of the Company, and this
Security is issued subject to such provisions of the Indenture with respect
thereto. Each Holder of this Security, by accepting the same, (a) agrees to and
shall be bound by such provisions, (b) authorizes and directs the Trustee on his
or her behalf to take such action as may be necessary or appropriate to
effectuate the subordination so provided and (c) appoints the Trustee as his or
her attorney-in-fact for any and all such purposes.

        The Indenture contains provisions for defeasance at any time of the
entire indebtedness of this Security or certain restrictive covenants and Events
of Default with respect to this Security, in each case upon compliance with
certain conditions set forth in the Indenture, except that the Company will not
be able to defease the right of the Holders to convert this Security pursuant to
Article Fourteen of the Indenture.

        Subject to the provisions of the Indenture, the Holder of this Security
is entitled, at its option, at any time on or before February 15, 2005 (except
that, in case this Security or any portion hereof shall be redeemed, such right
shall terminate with respect to this Security or portion hereof, as the case may
be, so redeemed at the close of business on the first Business Day next
preceding the date fixed for redemption as provided in the Indenture, unless the
Company defaults in making the payment due upon redemption or except as
otherwise provided in the Indenture), to convert the principal amount of this
Security (or any portion hereof which is $1,000 or an integral multiple thereof)
into fully paid and non-assessable shares of the Common Stock of the Company, as
said shares shall be constituted at the date of conversion, at the initial
Conversion Price specified below or at the adjusted Conversion Price in effect
at the date of conversion determined as provided in the Supplemental Indenture,
upon surrender of this Security, together with the conversion notice hereon duly
executed, to be accompanied (if so required by the Company) by instruments of
transfer, in form satisfactory to the Company and to the Trustee, duly executed
by the Holder or by its duly authorized attorney in writing. Such surrender
shall, if made during any period beginning at the close of business on a Regular
Record Date and ending at the opening of business on the Interest Payment Date
next following such Regular Record Date (unless this Security or the portion
being converted shall have been called for redemption on a Redemption Date
during the period beginning at the close of business on a Regular Record Date
and ending at the opening of business on the first




                                      -23-
<PAGE>   26

Business Day after the next succeeding Interest Payment Date, or if such
Interest Payment Date is not a Business Day, the second such Business Day), also
be accompanied by payment in funds acceptable to the Company of an amount equal
to the interest payable on such Interest Payment Date on the principal amount of
this Security then being converted. Subject to the aforesaid requirement for
payment and, in the case of a conversion after the Regular Record Date next
preceding any Interest Payment Date and on or before such Interest Payment Date,
to the right of the Holder of this Security (or any Predecessor Security) of
record at such Regular Record Date to receive an installment of interest (with
certain exceptions provided in the Indenture), no adjustment is to be made on
conversion for interest accrued hereon or for dividends on shares of Common
Stock issued on conversion. The initial Conversion Price of the Notes was
$140.569 per share of Common Stock. The initial Conversion Price was adjusted to
$70.2845 effective at the opening of business on February 17, 2000, to account
for the distribution by the Company at the close of business on February 16,
2000 of a stock dividend of one share of Common Stock for each share of Common
Stock outstanding. The Company is not required to issue fractional shares upon
any such conversion, but shall make adjustment therefor as provided in the
Indenture. The Conversion Price is subject to adjustment as provided in the
Indenture. In the event of conversion of this Security in part only, a new
Security or Securities for the unconverted portion hereof shall be issued in the
name of the Holder hereof upon the cancellation hereof.

        If an Event of Default with respect to Securities of this series shall
occur and be continuing, the principal of the Securities of this series may be
declared due and payable in the manner and with the effect provided in the
Indenture.

        The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the
Company and the rights of the Holders of the Securities of each series to be
affected under the Indenture at any time by the Company and the Trustee with the
consent of the Holders of more than 50% in principal amount of the Outstanding
Securities of each series to be affected. The Indenture also contains provisions
permitting the Holders of specified percentages in principal amount of the
Securities of each series at the time Outstanding, on behalf of the Holders of
all Securities of such series, to waive compliance by the Company with certain
provisions of the Indenture and certain past defaults under the Indenture and
their consequences. Any such consent or waiver by the Holder of this Security
shall be conclusive and binding upon such Holder and upon all future Holders of
this Security and of any Security issued upon the registration of transfer
hereof or in exchange herefor or in lieu hereof, whether or not notation of such
consent or waiver is made upon this Security.

        As provided in and subject to the provisions of the Indenture, the
Holder of this Security shall not have the right to institute any proceeding
with respect to the Indenture or for the appointment of a receiver or trustee or
for any other remedy thereunder, unless such Holder shall have previously given
the Trustee written notice of a continuing Event of Default with respect to the
Securities of this series, the Holders of not less than 25% in principal amount
of the Securities of this series at the time Outstanding shall have made written
request to the Trustee to institute proceedings in respect of such Event of
Default as Trustee and offered the Trustee reasonable indemnity, and the Trustee
shall not have received from the Holders of a majority in principal amount of
Securities of




                                      -24-
<PAGE>   27

this series at the time Outstanding a direction inconsistent with such request,
and shall have failed to institute any such proceeding, for 60 days after
receipt of such notice, request and offer of indemnity. The foregoing shall not
apply to any suit instituted by the Holder of this Security for the enforcement
of any payment of principal hereof or any premium or interest hereon on or after
the respective due dates expressed herein.

        No reference herein to the Indenture and no provision of this Security
or of the Indenture shall alter or impair the obligation of the Company, which
is absolute and unconditional, to pay the principal of and any premium and
interest on this Security at the times, place and rate, and in the coin or
currency, herein prescribed.

        As provided in the Indenture and subject to certain limitations therein
set forth, the transfer of this Security is registrable in the Security
Register, upon surrender of this Security for registration of transfer at the
office or agency of the Company in any place where the principal of and any
premium and interest on this Security are payable, duly endorsed by, or
accompanied by a written instrument of transfer in form satisfactory to the
Company and the Security Registrar duly executed by, the Holder hereof or its
attorney duly authorized in writing, and thereupon one or more new Securities of
this series and of like tenor, of authorized denominations and for the same
aggregate principal amount, will be issued to the designated transferee or
transferees.

        The Securities of this series are issuable only in registered form
without coupons in denominations of $1,000 and any integral multiple thereof. As
provided in the Indenture and subject to certain limitations therein set forth,
Securities of this series are exchangeable for a like aggregate principal amount
of Securities of this series and of like tenor of a different authorized
denomination, as requested by the Holder surrendering the same.

        No service charge shall be made for any such registration of transfer or
exchange, but the Company may require payment of a sum sufficient to cover any
tax or other governmental charge payable in connection therewith.

        Prior to due presentment of this Security for registration of transfer,
the Company, the Trustee and any agent of the Company or the Trustee may treat
the Person in whose name this Security is registered as the owner hereof for all
purposes, whether or not this Security be overdue, and neither the Company, the
Trustee nor any such agent shall be affected by notice to the contrary.

        This Security shall be deemed to be a contract made under the laws of
New York and for all purposes shall be construed in accordance with the laws of
New York, without regard to principles of conflicts of laws.

        All terms used in this Security which are defined in the Indenture shall
have the meanings assigned to them in the Indenture.



                                      -25-
<PAGE>   28

                                  ABBREVIATIONS

        The following abbreviations, when used in the inscription of the face of
this Security, shall be construed as though they were written out in full
according to applicable laws or regulations:


TEN COM   - as tenants in common           UNIF GIFT MIN ACT - ________
TEN ENT   - as tenants by the entireties
            (Cust)
JT TEN    - as joint tenants with right    Custodian ____________ under Uniform
            of survivorship and not as                  (Minor)
            tenants in common              Gifts to Minors Act ________________
                                                                     (State)

               Additional abbreviations may also be used though not in the above
list.



                                CONVERSION NOTICE

        To LSI Logic Corporation:

        The undersigned owner of this Security hereby irrevocably exercises the
option to convert this Security, or portion hereof (which is $1,000 or an
integral multiple thereof) below designated, into shares of Common Stock of the
Company in accordance with the terms of the Indenture referred to in this
Security, and directs that the shares issuable and deliverable upon the
conversion, together with any check in payment for fractional shares and any
Securities representing any unconverted principal amount hereof, be issued and
delivered to the registered Holder hereof unless a different name has been
indicated below. If this Notice is being delivered on a date after the close of
business on a Regular Record Date and prior to the opening of business on the
related Interest Payment Date (unless this Security or the portion thereof being
converted has been called for redemption on a Redemption Date after the close of
business on a Regular Record Date and prior to the opening of business on the
first Business Day after the next succeeding Interest Payment Date, or if such
Interest Payment Date is not a Business Day, the next such Business Day), this
Notice is accompanied by payment, in funds acceptable to the Company, of an
amount equal to the interest payable on such Interest Payment Date of the
principal of this Security to be converted. If shares are to be issued in the
name of a person other than the undersigned, the undersigned will pay all
transfer taxes payable with respect hereto. Any amount required to be paid by
the undersigned on account of interest accompanies this Security.



                                      -26-
<PAGE>   29

   Principal Amount to be Converted
(in an integral multiple of $1,000, if less
                  than all)
             $ ___________
                                                  Owner:

Dated: ____________                               ______________________________

                                                  ______________________________

                                                  Signature(s) must be
                                                  guaranteed by a qualified
                                                  guarantor institution with
                                                  membership in an approved
                                                  signature guarantee program
                                                  pursuant to Rule 17Ad-15 under
                                                  the Securities Exchange Act of
                                                  1934 if shares of Common Stock
                                                  are to be delivered, or
                                                  Securities to be issued, other
                                                  than to and in the name of the
                                                  registered owner.

                                                  ______________________________
                                                  Signature Guaranty

        Fill in for registration of shares of Common Stock and Security if to be
issued otherwise than to the registered Holder.



_________________________________              _________________________________
(Name)                                         Social Security or Other Taxpayer
                                               Identification Number
_________________________________
(Address)

_________________________________



                                      -27-
<PAGE>   30

                           OPTION TO ELECT REPURCHASE
                            UPON A FUNDAMENTAL CHANGE

To:     LSI Logic Corporation

        The undersigned registered owner of this Security hereby irrevocably
acknowledges receipt of a notice from LSI Logic Corporation (the "COMPANY") as
to the occurrence of a Fundamental Change with respect to the Company and
requests and instructs the Company to redeem the entire principal amount of this
Security, or the portion thereof (which is $1,000 or an integral multiple
thereof) below designated, in accordance with the terms of the Indenture
referred to in this Security at the redemption price, together with accrued
interest to, but excluding, such date, to the registered Holder hereof.

Dated: ____________

                                                  ______________________________

                                                  ______________________________
                                                  Signature(s)

                                                  Signature(s) must be
                                                  guaranteed by a qualified
                                                  guarantor institution with
                                                  membership in an approved
                                                  signature guarantee program
                                                  pursuant to Rule 17Ad-15 under
                                                  the Securities Exchange Act of
                                                  1934.

                                                  ______________________________
                                                  Signature Guaranty

Principal amount to be redeemed
(in an integral multiple of $1,000, if less than all):

___________________________________

NOTICE: The signature to the foregoing Election must correspond to the Name as
written upon the face of this Security in every particular, without alteration
or any change whatsoever.




                                      -28-