Security Agreement - STB Systems Inc. and Bank One, Texas, N.A.


                               SECURITY AGREEMENT


        THIS SECURITY AGREEMENT (this 'AGREEMENT') is made as of November 21,
1997, by STB Systems, Inc., a Texas corporation ('DEBTOR'), in favor of Bank
One, Texas, N.A., a national banking association, as Agent for the Lenders under
the Credit Agreement described below ('SECURED PARTY'). Debtor hereby agrees as
follows:

        Section 1. Definitions and Construction

        Section 1.1. General Definitions. Among the terms used in this Agreement
are the following:

        'COLLATERAL' means all property, of whatever type, which is described in
Section 2.1 as being at any time subject to a security interest hereunder to
Secured Party.

        'CREDIT AGREEMENT' means that certain Credit Agreement dated of even
date herewith among Debtor, Secured Party and certain lenders ('LENDERS'), as
from time to time amended, supplemented or restated.

        'SECURED OBLIGATIONS' has the meaning given it in Section 2.2.

        Section 1.2. Construction. All capitalized terms used in this Agreement
which are defined in the Credit Agreement and not otherwise defined herein shall
have the same meanings herein as set forth therein. All terms used in this
Agreement which are defined in the Uniform Commercial Code currently in effect
in the State of Texas (the 'CODE') and not otherwise defined herein or in the
Credit Agreement shall have the same meanings herein as set forth therein,
except where the context otherwise requires. Unless the context otherwise
requires or unless otherwise provided herein, references in this Agreement to a
particular agreement, instrument or document (including, but not limited to,
references in Section 2.1) also refer to and include all renewals, extensions,
amendments, modifications, supplements or restatements of any such agreement,
instrument or document, provided that nothing contained in this Section shall be
construed to allow, without written consent of Secured Party, any Person to
execute or enter into any such renewal, extension, amendment, modification,
supplement or restatement.

        Section 2. Security Interest

        Section 2.1. Grant of Security Interest. As collateral security for all
of the Secured Obligations, Debtor hereby pledges and assigns to Secured Party
and grants to Secured Party a continuing security interest, for the benefit of
Lenders, in all of the following (the 'COLLATERAL'):

        Accounts. All accounts (as defined in the Code) of any kind and all
        other rights to payment for goods sold or leased or for services which
        have been (or are to be) rendered, regardless




        of whether such accounts or other rights to payment have been earned by
        performance, all chattel paper, documents and instruments of any kind,
        relating to such accounts and all rights in, to or under all security
        agreements, leases and other contracts securing or otherwise relating to
        any such accounts, chattel paper, documents, or instruments (the
        'RECEIVABLES').

        Copyrights. All copyrights, and all copyrights of works based on,
        incorporated in, derived from or relating to works covered by such
        copyrights, and all right, title and interest to make and exploit all
        derivative works based on or adopted from works covered by such
        copyrights, all registrations with respect thereto, all applications
        with respect thereto, and all extensions and renewals with respect to
        any of the foregoing, together with all rights and interests associated
        with the foregoing.

        Equipment. All equipment in all of its forms, wherever located
        (including without limitation the foregoing in any respect, equipment
        used in farming or a profession, if any) (the 'EQUIPMENT').

        Instruments. All instruments in all forms (other than securities) and
        all interest, cash and other instruments or other writings or property
        from time to time received, receivable or otherwise distributed in
        respect of or in exchange for or in renewal or extension of any or all
        of the foregoing instruments (the 'INSTRUMENTS').

        Inventory. All inventory in all of its forms, whether held for sale,
        lease or otherwise, wherever located including, but not limited to, all
        (i) raw materials and work in process therefor, finished goods thereof,
        and materials used or consumed in the manufacture or production thereof,
        (ii) goods in which Obligor has an interest in mass or a joint or other
        interest or right of any kind, and (iii) goods which are returned to or
        repossessed by Obligor (the 'INVENTORY').

        General Intangibles, etc. All general intangibles of any kind
        (including, without limiting the foregoing in any respect, choses in
        action, tax refunds, and insurance proceeds), all chattel paper,
        documents, instruments, security agreements, leases, other contracts and
        money, and all other rights of Obligor (except those constituting
        Receivables to receive payments of money or the ownership of property)
        (the 'GENERAL INTANGIBLES').

        Trademarks. All trademarks, trade names, corporate names, company names,
        business names, fictitious business names, trade styles, service marks,
        logos and any other designs or sources of business identifiers, indicia
        of origin or similar devices, all registrations with respect thereto,
        all applications with respect to the foregoing, and all extensions and
        renewals with respect to any of the foregoing, together with all of the
        goodwill associated therewith, in each case whether now or hereafter
        existing, and all rights and interest associated with the foregoing.

        Other Collateral. To the extent not otherwise covered by the foregoing
        all chattel paper, documents, money and other types of personal
        property.

                                       -2-






        Lockbox; Bank Accounts. The Lockbox, the Collateral Account, and all
        funds and investments held in the Collateral Account from time to time
        or purchased with proceeds thereof, and any and all other moneys,
        securities or other property (and the proceeds therefrom) of the Debtor
        now or hereafter held or received by or in transit to Secured Party or
        any Lender from or for the account of Borrower, whether for safekeeping,
        custody, pledge, transmission, collection or otherwise, any and all
        deposits (general or special, time or demand, provisional or final) of
        the Debtor with Secured Party or any Lender, and any other credits and
        claims of the Debtor at any time existing against Secured Party or any
        Lender, including claims under certificates of deposit.

        Related Collateral and Proceeds. All books and records (including,
        without limitation, customer lists, computer software, computer
        hardware, computer disks and tapes and other materials and records) of
        Debtor pertaining in any way to any or all of the foregoing; all parts
        of, all accessions to, all replacements for, all products of, all
        payments of any type in lieu of or in respect of, and all documents and
        general intangibles covering or relating to any or all of the foregoing;
        all proceeds of any and all of the foregoing Collateral and, to the
        extent not otherwise included, all payments under insurance (whether or
        not Secured Party is the payee thereof) or under any indemnity, warranty
        or guaranty by reason of loss to or otherwise with respect to any of the
        foregoing Collateral.

In each case, the foregoing shall be covered by this Agreement, whether now or
hereafter existing, and whether Debtor's ownership or other rights therein are
now held or hereafter acquired and howsoever Debtor's interest therein may arise
or appear (whether by ownership, security interest, claim or otherwise).

        Section 2.2 Obligations Secured. The security interest created hereby in
the Collateral constitutes continuing collateral security for (i) the
'Obligations' as defined in the Credit Agreement, and of all amounts from time
to time owing by Debtor under the Credit Agreement, the Notes and the other Loan
Documents whether now existing or hereafter arising, (ii) all other loans and
future advances made by Lenders to Debtor and all other debts, obligations and
liabilities of every kind and character of Debtor now or hereafter existing in
favor of Secured Party or Lenders, whether such debts, obligations or
liabilities be direct or indirect, primary or secondary, joint or several, fixed
or contingent, and whether originally payable to Lenders or to a third party and
subsequently acquired by a Lender, and whether such debts, obligations or
liabilities are evidenced by notes, open account, overdraft, endorsement,
security agreement, guaranty, or otherwise (it being contemplated that Debtor
may hereafter become indebted to Lenders in further sum or sums but Lenders
shall have no obligation to extend further indebtedness by reason of this
Agreement) and (iii) the due performance and observance by Debtor of all of its
other obligations from time to time existing under or in respect of any of the
Loan Documents (collectively, the 'SECURED OBLIGATIONS').


                                       -3-






        Section 3. Representations, Warranties and Covenants

        Section 3.1 Representations and Warranties. Debtor represents and
warrants as follows:

(a)     Ownership and Liens. Debtor has good and marketable title to the
        Collateral free and clear of all liens, security interests, encumbrances
        or adverse claims, except for the security interest created by this
        Agreement. No dispute, right of setoff, counterclaim or defense exists
        with respect to all or any part of the Collateral. No effective
        financing statement or other instrument similar in effect covering all
        or any part of the Collateral is on file in any recording office except
        such as may have been filed in favor of Secured Party relating to this
        Agreement.

(b)     Security Interest. Debtor has and will have at all times full right,
        power and authority to grant a security interest in the Collateral to
        Secured Party in the manner provided herein, free and clear of any lien,
        security interest or other charge or encumbrance. This Agreement creates
        a valid and binding security interest in favor of Secured Party in the
        Collateral securing the Secured Obligations.

(c)     Location. Debtor's residence or chief executive office and principal
        place of business, as the case may be, and the office where the records
        concerning the Collateral are kept is located at its address set forth
        next to Debtor's signature below. Unless disclosed to the Secured Party
        in writing, all Collateral constituting Equipment and Inventory is
        located in the State of Texas.

        Section 3.2. Covenants. Unless Secured Party shall otherwise consent in
writing, Debtor will at all times comply with the covenants contained in this
Section 3.2.

(a)     Further Assurances. Debtor will, at its expense and at any time and from
        time to time, promptly execute and deliver all further instruments and
        documents and take all further action that may be necessary or desirable
        or that Secured Party may request in order (i) to perfect and protect
        the security interest created or purported to be created hereby and the
        first priority of such security interest; (ii) to enable Secured Party
        to exercise and enforce its rights and remedies hereunder in respect of
        the Collateral; or (iii) to otherwise effect the purposes of this
        Agreement.

(b)     Inspection of Collateral and Information. Debtor will keep adequate
        records concerning the Collateral and will permit Secured Party and all
        representatives appointed by Secured Party, including independent
        accountants, agents, attorneys, appraisers and any other persons to
        inspect any of the Collateral upon reasonable notice and the books and
        records of or relating to the Collateral at any time during normal
        business hours, and to make photocopies and photographs thereof, and to
        write down and record any information as such representatives shall
        obtain. Debtor will furnish to Secured Party any information which
        Secured Party may from time to

                                       -4-





        time reasonably request concerning any covenant, provision or
        representation contained herein or any other matter in connection with
        the Collateral.

(c)     Condition of Goods. Obligor will maintain, preserve, protect and keep
        all Collateral which constitutes goods in good condition, repair and
        working order (ordinary wear and tear excepted) and will cause such
        Collateral to be used and operated in a good and workmanlike manner, in
        accordance with applicable law and in a manner which will not make void
        or cancelable any insurance with respect to such Collateral. Obligor
        will promptly make or cause to be made all repairs, replacements and
        other improvements to or in connection with the Collateral which are
        necessary or desirable or that Secured Party may reasonably request to
        such end.

(d)     Insurance and Payment of Taxes, etc. Debtor will, at its own expense,
        maintain insurance with respect to all Collateral which constitutes
        goods in such amounts, against such risks, in such form and with such
        insurers, as shall be satisfactory to Secured Party from time to time.
        Debtor (i) will timely pay all property and other taxes, assessments and
        governmental charges or levies imposed upon the Collateral or any part
        thereof; (ii) will timely pay all lawful claims which, if unpaid, might
        become a lien or charge upon the Collateral or any part thereof; and
        (iii) will maintain appropriate accruals and reserves for all such
        liabilities in a timely fashion in accordance with generally accepted
        accounting principles. Debtor may, however, delay paying or discharging
        any such taxes, assessments, charges, claims or liabilities so long as
        the validity thereof is contested in good faith by proper proceedings
        and it has set aside on its books adequate reserves therefor.

(e)     Receivables and General Intangibles. Debtor will, except as otherwise
        provided herein, collect, at its own expense, all amounts due or to
        become due under each of the Receivables and General Intangibles. In
        connection with such collections, Debtor may (and, at Secured Party's
        direction, will) take such action as Debtor or Secured Party may deem
        necessary or advisable to enforce collection or performance of each of
        the Receivables and General Intangibles. Debtor will duly perform and
        cause to be performed all of its obligations with respect to the goods
        or services, the sale or lease or rendition of which gave rise or will
        give rise to each Receivable and all of its obligations to be performed
        under or with respect to the General Intangibles.

(f)     Delivery of Pledged Collateral. All instruments and writings
        constituting Instruments from time to time shall be delivered to Secured
        Party promptly upon the receipt thereof by or on behalf of Obligor. All
        such Instruments shall be held by or on behalf of Secured Party pursuant
        hereto and shall be delivered in suitable form for transfer by delivery
        with any necessary endorsement or shall be accompanied by fully executed
        instruments of transfer or assignment in blank, all in form and
        substance satisfactory to Secured Party.


                                       -5-





(g)     Transfer or Encumbrance. Debtor will not sell, assign (by operation of
        law or otherwise), transfer, exchange, lease or otherwise dispose of any
        of the Collateral, nor will Debtor grant a lien or security interest in
        or execute, file or record any financing statement or other security
        instrument with respect to the Collateral, nor will Debtor deliver
        actual or constructive possession of the Collateral to any other Person,
        other than: (i) sales or leases of Inventory in the ordinary course of
        business, and (ii) sale or other disposal, other than during the
        continuance of an Event of Default, of any item of Equipment which is
        worn out or obsolete and which has been replaced by an item of equal
        suitability and value, owned by Debtor and made subject to the security
        interest under this Agreement, but which is otherwise free and clear of
        any liens, security interest, encumbrance or adverse claim.

(h)     Possession and Compromise of Collateral. Debtor will not cause or permit
        the removal of any item of the Collateral from its possession, control
        and risk of loss. Debtor will not adjust, settle, compromise, amend or
        modify any of the Collateral, other than an adjustment, settlement,
        compromise, amendment or modification in good faith and in the ordinary
        course of business, other than during the continuance of an Event of
        Default, of any Receivable or General Intangible.

(I)     Financing Statement Filings. Debtor will not cause or permit any change
        to be made in its name, identity or corporate structure, or any change
        to be made to a jurisdiction other than as represented in Section 3.1
        hereof (i) in the location of any Collateral, (ii) the location of any
        records concerning any Collateral or (iii) in the location of Debtor's
        residence or chief executive office or chief place of business, as the
        case may be, unless Debtor shall have notified Secured Party of such
        change at lease thirty (30) days prior to the effective date of such
        change, and shall have first taken all action required by Secured Party
        for the purpose of further perfecting or protecting the security
        interest in favor of Secured Party in the Collateral.

(j)     Lockbox and Collateral Account. There is hereby established with Secured
        Party a cash collateral account (the 'COLLATERAL ACCOUNT') in the name
        and under the control of Secured Party into which there shall be
        deposited from time to time the cash proceeds of the Collateral required
        to be delivered to Secured Party pursuant to the following subsections
        of this Section 3.2 or pursuant to any other provision of this Agreement
        or any other Loan Document. Secured Party shall have the right, at any
        time and from time to time, to notify (or to require Debtor to notify)
        any and all obligors under any Receivables, General Intangibles,
        Instruments, or other rights to payment included among the Collateral of
        the assignment thereof to Secured Party under this Agreement and to
        direct such obligors to make payment of all amounts due or to become due
        to Debtor thereunder directly to Secured Party and, upon such
        notification and at the expense of Debtor and to the extent permitted by
        law, to enforce collection of any such Receivables, General Intangibles,
        Instruments, or other rights to payment and to adjust, settle or
        compromise the amount or payment thereof,

                                       -6-






        in the same manner and to the same extent as Debtor could have done.
        Debtor and Secured Party shall deal with the Collateral Account as
        follows:

             (i)    Debtor shall instruct all account debtors and other Persons
                    obligated to make payments to Debtor on any Receivables,
                    General Intangibles, Instruments, or other rights to payment
                    included within the Collateral to make such payments
                    directly to a post office box (the 'Lock Box') which shall
                    be in the name and under the control of Secured Party. So
                    long as no Default or Event of Default shall have occurred
                    and be continuing, all such payments received through the
                    Lock Box shall be deposited into an operating account of
                    Debtor. Upon the occurrence and during the continuance of a
                    Default or Event of Default, (i) all such payments made
                    through the Lock Box shall be deposited in the Collateral
                    Account and (ii) if the proceeds of any Collateral
                    (including any payments with respect to which instructions
                    have been given as provided above) shall be received by it,
                    Debtor shall as promptly as possible deposit such proceeds
                    into the Collateral Account. Until so deposited, all such
                    proceeds shall be held in trust by Debtor for Secured Party
                    and shall not be commingled with any other funds or property
                    of Debtor, and Debtor will not adjust, settle or compromise
                    the amount or payment of any such Receivable, General
                    Intangible, Instrument, or other right to payment or release
                    wholly or partly any account debtor or obligor thereof or
                    allow any credit or discount thereon if the amount thereof
                    exceeds $100,000 in the aggregate during each calendar month
                    (y) unless a Receivable in an amount at least equal to the
                    amount of the reduction of the Receivable so adjusted,
                    settled or compromised is substituted therefor in the
                    Borrowing Base, or (z) as a result thereof the Borrowing
                    Base, as redetermined immediately after such adjustment,
                    settlement or compromise, would equal or exceed the
                    outstanding principal balance of the Loans at such time.
                    Upon any such adjustment, settlement or compromise described
                    in the immediately preceding clause (z) a new Borrowing Base
                    Report shall be delivered to Agent and the Borrowing Base
                    shall be redetermined.

             (ii)   Amounts on deposit in the Collateral Account shall either
                    remain on deposit therein or be invested and re-invested
                    from time to time in such Liquid Investments as Secured
                    Party shall determine, which Liquid Investments shall be
                    held in the name and be under the control of Secured Party
                    until liquidated and applied as provided in the following
                    subsection (iii). Any income received by Secured Party with
                    respect to the balance from time to time standing to the
                    credit of the Collateral Account, including any interest on
                    or proceeds of Liquid Investments, shall also remain, or be
                    deposited, in the Collateral Account. All right, title and
                    interest in and to the amounts on deposit from time to time
                    in the Collateral Account, together with any Liquid
                    Investments from time to time made pursuant to this section
                    shall vest in Secured Party, shall constitute part of the
                    Collateral hereunder, and shall not

                                       -7-






                    constitute payment of the Secured Obligations until applied
                    thereto as herein provided.

             (iii)  Secured Party shall, at Secured Party's discretion, either
                    (A) continue to hold the balance of the Cash Collateral
                    Account and all Liquid Investments as Collateral, or (B)
                    apply any or all of the balance from time to time standing
                    to the credit of the Collateral Account (subject to
                    collection) as specified in Section 4.3 and liquidate any or
                    all Liquid Investments and apply the proceeds thereof as
                    specified in Section 4.3.

             (iV)   As used in this section, 'LIQUID INVESTMENT' means any
                    investment in the name of Secured Party (and, in the opinion
                    of counsel to Secured Party, appropriately subject to a
                    perfected security interest in favor of Secured Party) which
                    matures within one month after it is acquired by Secured
                    Party and is either (A) a certificate of deposit or time
                    deposit issued by Secured Party or (B) an obligation
                    entitled to the full faith and credit of the United States
                    which is in book-entry form and subject to pledge under
                    applicable state law and Treasury regulations.

        Section 4. Remedies, Powers and Authorizations

        Section 4.1. Provisions Concerning the Collateral

        (a)         Power of Attorney. If Default or Potential Default Exists,
                    Debtor hereby irrevocably appoints Secured Party as Debtor's
                    attorney-in-fact and proxy, with full authority in the place
                    and stead of Debtor and in the name of Debtor or otherwise,
                    from time to time in Secured Party's reasonable discretion,
                    to take any action and to execute any instrument which
                    Secured Party may reasonably deem necessary or advisable to
                    accomplish the purposes of this Agreement.

        (b)         Performance by Secured Party. If Debtor fails to perform any
                    agreement or obligation contained herein, Secured Party may
                    itself perform, or cause performance of, such agreement or
                    obligation, and the expenses of Secured Party incurred in
                    connection therewith shall be payable by Debtor under
                    Section 4.5.

        Section 4.2. Event of Default - Remedies. If an Event of Default shall
have occurred and be continuing, and without limiting other rights and remedies
provided herein, under the Loan Documents or otherwise available to Secured
Party, Secured Party may from time to time in its discretion, without limitation
and without notice (a) exercise in respect of the Collateral all the rights and
remedies of a secured party on default under the Code (whether or not the Code
applies to the affected Collateral); (b) require Debtor to, and Debtor hereby
agrees that it will at its expense and upon request of Secured Party forthwith,
assemble all or part of the Collateral as directed by Secured Party and make it
available to Secured Party at a place to be designated by Secured Party which is
reasonably convenient to both parties; (c) reduce its claim to judgment or
foreclose or otherwise

                                       -8-





enforce, in whole or in part, the security interest created hereby by any
available judicial procedure; or (d) apply by appropriate judicial proceedings
for appointment of a receiver for the Collateral, or any part thereof, and
Debtor hereby consents to any such appointment. Debtor agrees that, to the
extent notice of sale shall be required by law, at least ten (10) days' notice
to Debtor of the time and place of any public sale or the time after which any
private sale is to be made shall constitute reasonable notification. Secured
Party shall not be obligated to make any sale of Collateral regardless of notice
of sale having been given. Secured Party may adjourn any public or private sale
from time to time by announcement at the time and place fixed therefor, and such
sale may, without further notice, be made at the time and place to which it was
so adjourned.

        Section 4.3. Application of Proceeds. If any Default or Event of Default
shall have occurred and be continuing, Secured Party may in its discretion apply
any cash held by Secured Party as Collateral, and any cash proceeds received by
Secured Party in respect of any sale of, collection from, or other realization
upon all or any part of the Collateral, to any or all of the following in such
order as Secured Party may elect: (a) to the repayment of the reasonable costs
and expenses, including reasonable attorneys' fees and legal expenses, incurred
by Secured Party in connection with (i) the administration of this Agreement,
(ii) the custody, preservation, use or operation of, or the sale of, collection
from, or other realization upon, any Collateral, (iii) the exercise or
enforcement of any of the rights of Secured Party hereunder, or (iv) the failure
of Debtor to perform or observe any of the provisions hereof; (b) to the payment
or other satisfaction of any liens and other encumbrances upon any of the
Collateral; (c) to the satisfaction of any other Secured Obligations; (d) by
holding the same as Collateral; (e) to the payment of any other amounts required
by applicable law (including, without limitation, Section 9.504(a)(3) of the
Code or any successor or similar, applicable statutory provision); and (f) by
delivery to Debtor or to whomsoever shall be lawfully entitled to receive the
same or as a court of competent jurisdiction shall direct.

        Section 4.4. Deficiency. In the event that the proceeds of any sale,
collection or realization of or upon Collateral by Secured Party are
insufficient to pay all amounts to which Secured Party is legally entitled,
Debtor shall be liable for the deficiency, together with interest thereon at
such other rate as shall be fixed by applicable law, together with the costs of
collection and the reasonable fees of any attorneys employed by Secured Party to
collect such deficiency.

        Section 4.5. Indemnity and Expenses.

        (a)         Debtor hereby indemnifies and agrees to hold harmless
                    Secured Party and each Lender and their respective officers,
                    directors, employees, agents and counsel (each an
                    'INDEMNIFIED PERSON') from and against any and all
                    liabilities, obligations, claims, losses, damages,
                    penalties, actions, judgments, suits, costs, expenses or
                    disbursements of any kind or nature whatsoever ('CLAIMS AND
                    LIABILITIES') which may be imposed on, incurred by, or
                    asserted against any Indemnified Person growing out of or
                    resulting from this Agreement and the transactions and
                    events at any time associated therewith. THE FOREGOING
                    INDEMNIFICATION SHALL APPLY WHETHER OR NOT SUCH CLAIMS AND
                    LIABILITIES ARE IN ANY WAY OR TO ANY EXTENT OWED, IN WHOLE
                    OR IN PART,

                                       -9-





                    UNDER ANY CLAIM OR THEORY OF STRICT LIABILITY, OR ARE CAUSED
                    IN WHOLE OR IN PART BY ANY NEGLIGENT ACT OR OMISSION BY ANY
                    INDEMNIFIED PERSON, except to the limited extent any Claims
                    and Liabilities of an Indemnified Person are proximately
                    caused by such Indemnified Person's gross negligence or
                    willful misconduct. The indemnification provided for in this
                    section shall survive the termination of this Agreement.

        (b)         Debtor will upon demand pay to Secured Party the amount of
                    any and all reasonable costs and expenses, including the
                    fees and disbursements of Secured Party's counsel and of any
                    experts and agents, which Secured Party may incur in
                    connection with (i) the transaction which give rise to this
                    Agreement; (ii) the preparation of this Agreement and the
                    perfection and preservation of this security interest
                    created under this Agreement; (iii) the administration of
                    this Agreement; (iv) the custody, preservation, use or
                    operation of, or the sale of, collection from, or other
                    realization upon, any Collateral; (v) the exercise or
                    enforcement of any of the rights of Secured Party hereunder;
                    or (vi) the failure by Debtor to perform or observe any of
                    the provisions hereof, except expenses resulting from
                    Secured Party's gross negligence or willful misconduct.

Section 5. Miscellaneous

        Section 5.1. Waiver and Amendment. No failure or delay by Secured Party
in exercising any right, power or remedy which Secured Party may have under this
Agreement shall operate as a waiver thereof or of any other right, power of
remedy, nor shall any single or partial exercise by Secured Party of any such
right, power or remedy preclude any other or future exercise thereof or of any
other right, power or remedy. No waiver of any provision of this Agreement and
no consent to any departure therefrom shall ever be effective unless it is in
writing and signed by Secured Party, and then such waiver or consent shall be
effective only in the specific instances and for the purposes for which given
and to the extent specified in such writing. No modification or amendment of or
supplement to this Agreement shall be valid or effective unless the same is in
writing and signed by the party against whom it is sought to be enforced. In
addition, all such amendments and waivers shall be effective only if given with
the necessary approvals of Lenders as required in the Credit Agreement.

        Section 5.2. Notices. Any notice or communication required or permitted
hereunder shall be given as provided in the Credit Agreement.

        Section 5.3. Preservation of Rights. No failure on the part of Secured
Party to exercise, and no delay in exercising, any right hereunder or under any
other Loan Document shall operate as a waiver thereof; nor shall any single or
partial exercise of any such right preclude any other or further exercise
thereof or the exercise of any other right. The rights and remedies of Secured
Party provided herein are cumulative and are in addition to, and not exclusive
of, any rights or remedies provided by law.


                                      -10-





        Section 5.4. Binding Effect and Assignment. This Agreement creates a
continuing security interest in the Collateral and (a) shall be binding on
Debtor and its successors and permitted assigns and (b) shall inure, together
with all rights and remedies of Secured Party hereunder, to the benefit of
Secured Party and Lenders and their respective successors, transferees and
assigns. None of the rights or obligations of Debtor hereunder may be assigned
or otherwise transferred without the prior written consent of Secured Party.

        Section 5.5. Termination. It is contemplated by the parties hereto that
there may be times when no Secured Obligations are outstanding, but
notwithstanding such occurrences, this Agreement shall remain valid and shall be
in full force and effect as to subsequent outstanding Secured Obligations. Upon
written request for the termination hereof delivered by Debtor to Secured Party,
if no Secured Obligations are outstanding, and the Credit Agreement and the
commitment of Lenders to extend credit to Debtor have terminated or expired,
this Agreement and the security interest created hereby shall terminate and
Secured Party will at Debtor's expense, (a) return to Debtor such of the
Collateral as shall not have been sold or otherwise disposed of or applied
pursuant to the terms hereof; and (b) execute and deliver to Debtor such
documents as Debtor shall reasonably request to evidence such termination.

        SECTION 5.8. GOVERNING LAW. THIS AGREEMENT SHALL BE GOVERNED BY AND
CONSTRUED AND ENFORCED IN ACCORDANCE WITH THE LAWS OF THE STATE OF TEXAS AND THE
LAWS OF THE UNITED STATES OF AMERICA; EXCEPT TO THE EXTENT THAT THE PERFECTION
AND THE EFFECT OF PERFECTION OR NON-PERFECTION OF THE SECURITY INTEREST CREATED
HEREBY ARE GOVERNED BY THE LAWS OF A JURISDICTION OTHER THAN THE STATE OF TEXAS.


                                      -11-






        IN WITNESS WHEREOF, Debtor has caused this Agreement to be executed and
delivered by its officer thereunto duly authorized, as of the date first above
written.


Address:                              STB SYSTEMS, INC.

P.O. Box 850957
1651 N. Glenville
Richardson TX 75085-0957
                                      By:  /s/  AUTHORIZED OFFICER
                                         ------------------------------------
                                         Name:
                                         Title:

                                      -12-




 TYPE:  EX-10.11.6
 SEQUENCE:  7
 DESCRIPTION:  EX-10.11.6




                                                                 EXHIBIT 10.11.6

                      FIRST AMENDMENT TO SECURITY AGREEMENT

        THIS FIRST AMENDMENT TO SECURITY AGREEMENT (this 'Amendment') dated as
of December 21, 1999, is made by STB Systems, Inc., a Texas corporation
('Debtor') and Bank One, Texas, N.A., individually and as Agent for the Lenders
under the Credit Agreement described below ('Secured Party').

                                   BACKGROUND

        1.   Debtor, Secured Party and the lenders named therein entered into
that certain Credit Agreement dated as of November 21, 1997, (as heretofore
amended, supplemented, or restated, the 'Original Credit Agreement'), for the
purpose and consideration therein expressed, pursuant to which Debtor executed
(i) in favor of Bank One, Texas, N.A. ('Bank One') that certain promissory note
dated as of November 23, 1999, payable to the order of Bank One in the aggregate
principal amount of $12,500,000 (the 'Original Bank One Note') and (ii) in favor
of Comerica Bank-Texas ('Comerica') that certain promissory note dated as of
November 23, 1999, payable to the order of Comerica in the aggregate principal
amount of $12,500,000; in each case which renewed and extended the promissory
notes described therein (the 'Original Comerica Note'; the Original Bank One
Note and the Original Comerica Note are herein collectively referred to as the
'Original Notes').

        2.   Pursuant to the Original Credit Agreement, Debtor executed in favor
of Secured Party that certain Security Agreement dated as of November 21, 1997
(the 'Original Security Agreement');

        3.   Debtor, Secured Party and the lenders named therein are or are to
become parties to an Amended and Restated Credit Agreement of even date herewith
(as amended, supplemented, or restated, the 'Credit Agreement'), amending and
restating the Original Credit Agreement for the purpose and consideration
therein expressed.

        4.   Pursuant to the Credit Agreement, Debtor executed (i) in favor of
Bank One that certain promissory note of even date herewith, payable to the
order of Bank One in the aggregate principal amount of $12,500,000, renewing and
extending the Original Bank One Note (the 'New Bank One Note') and (ii) in favor
of Comerica that certain promissory note of even date herewith, payable to the
order of Comerica in the aggregate principal amount of $12,500,000, renewing and
extending the Original Comerica Note (the 'New Comerica Note'; the New Bank One
Note and the New Comerica Note, as from time to time amended, and all promissory
notes given in substitution, renewal or extension therefore or thereof, in whole
or in part, being herein collectively called the 'Notes'); and

        4.   Pursuant to the Credit Agreement, Lenders have agreed to extend
credit to Debtor.

        5.   In order to induce Lenders to extend such credit pursuant to the
Credit Agreement, Debtor has agreed to enter into this Amendment for the
purposes as stated herein.




        NOW, THEREFORE, in consideration of the premises and for other good and
valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, Debtor and Secured Party hereby agree as follows:


                                    AGREEMENT

        1.   DEFINED TERMS. Capitalized terms used but not defined herein shall
have the meanings given them in the Credit Agreement.

        2.   OTHER DEFINED TERMS. Unless the context otherwise requires, the
following terms when used in this Amendment shall have the meanings assigned to
them in this Section 2.

             'Amendment' means this First Amendment to Security Agreement.

             'Security Agreement' means the Original Security Agreement as
        amended hereby.

        3.   AMENDMENTS TO ORIGINAL SECURITY AGREEMENT.

             A. General Definitions. The definition of 'Credit Agreement' in
        Section 1.1 of the Original Security Agreement is hereby amended in its
        entirety to read as follows:

             'CREDIT AGREEMENT' means that certain Amended and Restated Credit
        Agreement dated as of December 21, 1999, among Debtor, Secured Party and
        certain lenders (the 'LENDERS'), as from time to time amended,
        supplemented or restated.'

             B. Terms. Secured Party and Debtor hereby agree that (i) all
        references to the 'Notes' in the Original Security Agreement shall be
        deemed to refer to the Notes as defined herein and (ii) all references
        to the 'Loan Documents' in the Original Security Agreement shall be
        deemed to refer to the Loan Documents as defined in the Credit
        Agreement.

             C. Address. Debtor's address on the signature page of the Original
        Security Agreement is hereby amended in its entirety to read as follows:

                             '3400 Waterview
                             Richardson, TX 75080'

        3.   RATIFICATION OF ORIGINAL SECURITY AGREEMENT. Debtor acknowledges
that its obligations and covenants under the Original Security Agreement are not
impaired by the execution and delivery of the Notes or the Credit Agreement and
shall remain in full force and effect. The Original Security Agreement as hereby
amended is hereby ratified and confirmed in all respects. Any reference to the
Security Agreement in any Loan Document shall be deemed to refer to this
Amendment also. The execution, delivery and effectiveness of this



                                       2


Amendment shall not, except as expressly provided herein, operate as a wavier of
any right, power or remedy of Secured Party or Lenders under the Original
Security Agreement or any other Loan Document nor constitute a waiver of any
provision of the Original Security Agreement or any other Loan Document. This
Amendment is a Loan Document, and all provisions in the Credit Agreement
pertaining to Loan Documents apply hereto.

        4.   FURTHER ASSURANCES. Debtor will, at its expense and at any time and
from time to time, promptly execute and deliver all further instruments and
documents and take all further action that may be necessary or desirable or that
Secured Party may request in order (i) to perfect, continue the perfection of,
and protect the security interest created or purported to be created by the
Security Agreement and the first priority of such security interest; (ii) to
enable Secured Party to exercise and enforce its rights and remedies thereunder
in respect of the Collateral; or (iii) to otherwise effect the purposes of the
Security Agreement, including but not limited to: (A) executing and filing such
financing or continuation statements, or amendments thereto, as may be necessary
or desirable or that Secured Party may request in order to perfect, continue the
perfection of, and preserve the security interest created or purported to be
created thereby; (B) delivering to Secured Party (upon request, to the extent
not otherwise required hereunder to be delivered without request) all originals
of chattel paper, documents or instruments which are from time to time included
in the Collateral; and (C) furnishing to Secured Party from time to time
statements and schedules further identifying and describing the Collateral and
such other reports in connection with the Collateral as Secured Party may
reasonably request, all in reasonable detail.

        5.   GOVERNING LAW. THIS AMENDMENT SHALL BE GOVERNED BY AND CONSTRUED
AND ENFORCED IN ACCORDANCE WITH THE LAWS OF THE STATE OF TEXAS AND THE LAWS OF
THE UNITED STATES OF AMERICA; EXCEPT TO THE EXTENT THAT THE PERFECTION AND THE
EFFECT OF PERFECTION OR NON-PERFECTION OF THE SECURITY INTEREST CREATED HEREBY
ARE GOVERNED BY THE LAWS OF A JURISDICTION OTHER THAN THE STATE OF TEXAS.

        6.   COUNTERPARTS. This Amendment may be separately executed in
counterparts and by the different parties hereto in separate counterparts, each
of which when so executed shall be deemed to constitute one and the same
Amendment. This Amendment may be validly executed by facsimile or other
electronic transmission.



            [The remainder of this page is intentionally left blank]



                                       3


        IN WITNESS WHEREOF, the undersigned have executed this Amendment as of
the date first above written.

                                       DEBTOR:

                                       STB SYSTEMS, INC.

                                       By: /s/  BRYAN F. KEYES
                                          ------------------------------------
                                       Name:
                                       Title: Vice President

                                       SECURED PARTY:
                                       BANK ONE, TEXAS, N.A., as Agent

                                       By:  /s/ RICK ROGERS
                                          ------------------------------------
                                       Name:
                                       Title: Managing Director