[EXECUTION]


                         FIRST AMENDMENT TO CREDIT AGREEMENT

     THIS FIRST AMENDMENT TO CREDIT AGREEMENT (herein called this "Amendment")
made as of January 30,1998 by and among STB Systems, Inc., a Texas corporation
(herein called "Borrower"), Bank One, Texas, N.A., individually and as agent
(herein called "Agent") and the Lenders referred to in the Original Credit
Agreement described below ("Original Lenders").


                                     WITNESSETH:

     WHEREAS, Borrower and Lenders have entered into that certain Credit
Agreement dated as of November 21, 1997 (the "Original Agreement"), for the
purposes and consideration therein expressed, pursuant to which Lenders became
obligated to make loans to Borrower as therein provided; and

     WHEREAS, Borrower and Lenders desire to amend the Original Agreement to
increase the commitment amount, add an additional Lender and amend certain other
terms and provisions thereof;

     NOW, THEREFORE, in consideration of the premises and the mutual covenants
and agreements contained herein and in the Original Agreement, in consideration
of the loans which may hereafter be made by Lenders to Borrower, and for other
good and valuable consideration, the receipt and sufficiency of which are hereby
acknowledged, the parties hereto do hereby agree as follows:

                                      ARTICLE I.

                              DEFINITIONS AND REFERENCES

     Section 1.1 TERMS DEFINED IN THE ORIGINAL AGREEMENT. Unless the context
otherwise requires or unless otherwise expressly defined herein, the terms
defined in the Original Agreement shall have the same meanings whenever used in
this Amendment.

     Section 1.2. 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 1.2.

          "AMENDMENT" means this First Amendment to Credit Agreement.

          "AMENDMENT DOCUMENTS" means this Amendment and the Renewal Notes.




          "CREDIT AGREEMENT" means the Original Agreement as amended hereby.

          "LENDERS" means, collectively, the Original Lenders and Comerica Bank-
California.


                                     ARTICLE II.

                           AMENDMENTS TO ORIGINAL AGREEMENT

     Section 2.1. The definition of "COMMITMENT" in Section 1.1. of the Original
Agreement is hereby amended in its entirety to read as follows:

          "'COMMITMENT' means the amount of $40,000,000."

     Section 2.2. The definition of "MAJORITY LENDERS" in Section 1.1 of the
Original Agreement is hereby amended in its entirety to read as follows:

          "'MAJORITY LENDERS' means Lenders whose aggregate Percentage Shares
equal or exceed seventy-five percent (75 %)."

     Section 2.3. COMMITMENT FEES. Subsection 2.5(a)(ii) of the Original
Agreement is hereby amended in its entirety to read as follows:

     "(ii) In consideration of the commitment of each Lender except for Bank
     One, to make Loans, Borrower will pay to Agent for the account of each such
     Lender, a commitment fee determined on a daily basis by applying a rate of
     twenty-five basis points (0.25%) per annum to each such Lender's Percentage
     Share of the unused portion of the Commitment on each day during the
     Commitment Period, determined for each such day by deducting from the
     amount of the Commitment at the end of such day the Facility Usage. This
     commitment fee shall be due and payable in arrears on the tenth day of each
     Fiscal Quarter for the immediately preceding Fiscal Quarter and at the end
     of the Commitment Period.

                                     ARTICLE III.

                              ASSIGNMENT AND ACCEPTANCE

     Bank One and Sanwa (in this article, Bank One and Sanwa are collectively
called "Assignors") and Comerica Bank - California ("Assignee"), hereby agree as
follows:


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     Section 3.1. Assignors hereby sell and assign to Assignee, without recourse
and without representation or warranty except as expressly set forth herein, and
Assignee hereby purchases and assumes from Assignors, an interest in and to
Assignors' rights and obligations under the Credit Agreement and the other Loan
Documents as of the date hereof equal to the percentage interest specified on
Annex I hereto of ALL OUTSTANDING RIGHTS AND OBLIGATIONS under the Credit
Agreement and the other Loan Documents. After giving effect to such sale and
assignment, Assignee's and Assignors' Percentage Shares of the Commitment and
the amount of Assignee's and Assignors' Percentage Share of Outstanding Loans
will be as set forth on Annex I hereto.

     Section 3.2. Bank One, with respect to the interests assigned by it
hereunder (a) represents and warrants that with respect to the interests
assigned by it hereunder, it is the legal and beneficial owner of the interest
being assigned by it hereunder and that such interest is free and clear of any
adverse claim; (b) makes no representation or warranty and assumes no
responsibility with respect to any statements, warranties or representations
made in or in connection with the Loan Documents or the execution, legality,
validity, enforceability, genuineness, sufficiency or value of the Loan
Documents or any other instrument or document furnished pursuant thereto; (c)
makes no representation or warranty and assumes no responsibility with respect
to the financial condition of any Restricted Person or the performance or
observance by any Restricted Person of any of its obligations under the Loan
Documents or any other instrument or document furnished pursuant thereto; and
(d) delivers herewith the Note held by Bank One and requests that Agent exchange
such Note for new Notes payable to the order of Assignee in an amount equal to
the Percentage Share of the Commitment assumed by Assignee pursuant hereto and
to Bank One in an amount equal to the Percentage Share of the Commitment
retained by the Bank One as specified on Annex I.

     Section 3.3. Sanwa, with respect to the interests assigned by it hereunder
(a) represents and warrants that with respect to the interests assigned by it
hereunder, it is the legal and beneficial owner of the interest being assigned
by it hereunder and that such interest is free and clear of any adverse claim;
(b) makes no representation or warranty and assumes no responsibility with
respect to any statements, warranties or representations made in or in
connection with the Loan Documents or the execution, legality, validity,
enforceability, genuineness, sufficiency or value of the Loan Documents or any
other instrument or document furnished pursuant thereto; (c) makes no
representation or warranty and assumes no responsibility with respect to the
financial condition of any Restricted Person or the performance or observance by
any Restricted Person of any of its obligations under the Loan Documents or any
other instrument or document furnished pursuant thereto; and (d) delivers
herewith the Note held by Sanwa and requests that Agent exchange such Note for
new Notes payable to the order of Assignee in an amount equal to the Percentage
Share of the Commitment assumed by Assignee pursuant hereto and to Sanwa in an
amount equal to the Percentage Share of the Commitment retained by the Sanwa as
specified on Annex I.

     Section 3.4. Assignee (a) confirms that it has received a copy of the
Credit Agreement, together with copies of the financial statements referred to
in Section 6.2 thereof and such other


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documents and information as it has deemed appropriate to make its own credit
analysis and decision to enter into this Amendment; (b) agrees that it will,
independently and without reliance upon Agent, Assignors or any other Lender and
based on such documents and information as it shall deem appropriate at the
time, continue to make its own credit decisions in taking or not taking action
under the Credit Agreement; (c) confirms that it is an Eligible Transferee; (d)
appoints and authorizes Agent to take such action as agent on its behalf and to
exercise such powers and discretion under the Credit Agreement as are delegated
to Agent by the terms thereof, together with such powers and discretion as are
reasonably incidental thereto; (e) agrees that it will perform in accordance
with their terms all of the obligations that by the terms of the Credit
Agreement are required to be performed by it as a Lender; and (f) delivers
herewith any U.S. Internal Revenue Service or other forms required under Section
3.6(d).

     Section 3.5. Upon such acceptance and recording by Agent, (a) Assignee
shall be a party to the Credit Agreement and, to the extent provided in this
Amendment, have the rights and obligations of a Lender thereunder and (b)
Assignors shall, to the extent provided in this Article, relinquish their rights
and be released from their obligations under the Credit Agreement.

     Section 3.6. Upon such acceptance and recording by Agent, from and after
the effective date of this Amendment, Agent shall make all payments under the
Credit Agreement and the Notes in respect of the interest assigned hereby
(including, without limitation, all payments of principal, interest and
commitment fees with respect thereto) to Assignee. Assignors and Assignee shall
make all appropriate adjustments in payments under the Credit Agreement and the
Notes for periods prior to the effective date of this Amendment directly between
themselves.


                                     ARTICLE IV.

                             CONDITIONS OF EFFECTIVENESS

     Section 4.1. EFFECTIVE DATE. This Amendment shall become effective as of
the date first above written when, and only when all of the following have been
satisfied:

          (a)  DOCUMENTS. Agent shall have received, at Agent's office, and
     executed by, if applicable, Lenders, Borrower and/or Guarantors, all of the
     following documents in form and substance satisfactory to Agent:

               (i)    this Amendment;

               (ii)   the Notes with appropriate insertions, in the form
          attached hereto as Exhibit A, payable to the order of each Lender on
          or before the Maturity Date (such Notes herein called the "Renewal
          Notes"), in a principal amount equal to the amount set out in Annex I
          hereto;


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               (iii)  Consents of Guarantors in a form satisfactory to Agent;

               (iv)   the written opinion of Borrower's counsel dated as of the
          date of this Amendment, addressed to Agent, to the effect that this
          Amendment and each Renewal Note has been duly authorized, executed and
          delivered by Borrower and that the Credit Agreement and each Renewal
          Note constitute the legal, valid and binding obligations of Borrower,
          enforceable in accordance with their terms (subject, as to enforcement
          of remedies, to applicable bankruptcy, reorganization, insolvency and
          similar laws and to general principles of equity);

               (v)    a certificate of the Secretary of Borrower dated the date
          of this Amendment certifying that (A) attached thereto is a true and
          complete copy of resolutions adopted by the Board of Directors of
          Borrower authorizing the execution, delivery and performance of this
          Amendment and each Renewal Note and certifying the names and true
          signatures of the officers of Borrower authorized to sign this
          Amendment and each Renewal Note and (B) all of the representations and
          warranties set forth in Article V hereof are true and correct at and
          as of the time of such effectiveness; and

               (vi)   such other supporting documents as Agent may reasonably
          request.

          (b)  FEES. Agent shall have received, for the benefit of Lenders, an
     additional facility fee in the amount of $20,000.


                                      ARTICLE V.

                            REPRESENTATIONS AND WARRANTIES

     Section 5.1. REPRESENTATIONS AND WARRANTIES OF BORROWER. In order to induce
each Lender to enter into this Amendment, Borrower represents and warrants as to
itself and each Restricted Person, to Lenders that:

          (a)  All representations and warranties contained in Article V of the
     Original Agreement are true on and as of the date hereof (except to the
     extent that the facts upon which such representations are based have been
     changed by transactions and events expressly permitted by the Credit
     Agreement.

          (b)  Borrower is duly authorized to execute and deliver this Amendment
     and each Renewal Note and is and will continue to be duly authorized to
     borrow monies and to perform its obligations under the Credit Agreement.
     Each Restricted Person has duly taken all corporate action necessary to
     authorize the execution and delivery of this


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     Amendment and each Renewal Note and to authorize the performance of the
     obligations hereunder and thereunder.

          (c)  The execution and delivery by Borrower of this Amendment and each
     Renewal Note, the performance by Borrower of its obligations hereunder and
     thereunder and the consummation of the transactions contemplated hereby and
     thereby do not and will not conflict with any provision of law, statute,
     rule or regulation or of the articles of incorporation and bylaws of
     Borrower, or of any material agreement, judgment, license, order or permit
     applicable to or binding upon Borrower, or result in the creation of any
     lien, charge or encumbrance upon any assets or properties of Borrower.
     Except for those which have been obtained, no consent, approval,
     authorization or order of any court or governmental authority or third
     party is required in connection with the execution and delivery by Borrower
     of this Amendment and each Renewal Note or to consummate the transactions
     contemplated hereby and thereby.

          (d)  When duly executed and delivered, each of this Amendment, the
     Credit Agreement and the Renewal Notes will be a legal and binding
     obligation of Borrower, enforceable in accordance with its terms, except as
     limited by bankruptcy, insolvency and similar laws applying to creditors'
     rights generally and by principles of equity applying to creditors' rights
     generally.

          (e)  The Consolidated financial statements of Borrower dated as of
     October 31, 1997 fairly present the Consolidated financial position at such
     dates and the Consolidated statement of operations and the changes in
     Consolidated financial position for the periods ending on such dates for
     Borrower. Copies of such financial statements have heretofore been
     delivered to Agent. Since October 31, 1997, no material adverse change has
     occurred in the financial condition or businesses or in the Consolidated
     financial condition or businesses of Borrower.


                                     ARTICLE VI.

                                    MISCELLANEOUS

     Section 6.1. RATIFICATION OF AGREEMENTS. The Original Agreement as hereby
amended is hereby ratified and confirmed in all respects. The Loan Documents, as
they may be amended or affected by the various Amendment Documents, are hereby
ratified and confirmed in all respects. Any reference to the Credit Agreement in
any Loan Document shall be deemed to be a reference to the Original Agreement as
hereby amended. Any reference to the Notes in any other Loan Document shall be
deemed to be a reference to the Renewal Notes issued and delivered pursuant to
this Amendment. Any reference to Lenders in any other Loan Document shall be
deemed to be a reference to the Lenders signatory hereto. The execution,
delivery and effectiveness of this Amendment and the Renewal Notes shall not,
except as expressly provided herein or therein,


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operate as a waiver of any right, power or remedy of Lenders under the Credit
Agreement, the Notes, or any other Loan Document nor constitute a waiver of any
provision of the Credit Agreement, the Notes or any other Loan Document.

     Section 6.2. SURVIVAL OF AGREEMENTS. All representations, warranties,
covenants and agreements of Borrower herein shall survive the execution and
delivery of this Amendment and the performance hereof, including without
limitation the making or granting of the Loans and the issuance and delivery of
the Renewal Notes, and shall further survive until all of the Obligations are
paid in full. All statements and agreements contained in any certificate or
instrument delivered by Borrower any Restricted Person hereunder or under the
Credit Agreement to any Lender shall be deemed to constitute representations and
warranties by, and/or agreements and covenants of, Borrower under this Amendment
and under the Credit Agreement.

     Section 6.3. LOAN DOCUMENTS. This Amendment and each Renewal Note are each
a Loan Document, and all provisions in the Credit Agreement pertaining to Loan
Documents apply hereto and thereto.

     Section 6.4. GOVERNING LAW. This Amendment shall be governed by and
construed in accordance with the laws of the State of Texas and any applicable
laws of the United States of America in all respects, including construction,
validity and performance.

     Section 6.5. 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 AND THE OTHER LOAN DOCUMENTS REPRESENT THE FINAL AGREEMENT
BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS, OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES. THERE ARE NO
UNWRITTEN ORAL AGREEMENTS OF THE PARTIES.

               [THE REMAINDER OF THIS PAGE IS INTENTIONALLY LEFT BLANK]


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

                                        STB SYSTEMS, INC.
                                        Borrower

                                        By:  /s/ James L. Hopkins
                                           --------------------------------
                                           Name: James L. Hopkins
                                           Title: Vice President, Chief
                                                  Financial Officer

                                        BANK ONE, TEXAS, N.A.
                                        Agent and Lender

                                        By: ILLEGIBLE
                                           --------------------------------
                                           Name:
                                           Title:

                                        SANWA BUSINESS CREDIT CORPORATION
                                        Lender

                                        By: ILLEGIBLE
                                           --------------------------------
                                           Name:
                                           Title:

                                        COMERICA BANK-CALIFORNIA
                                        Lender

                                        By: ILLEGIBLE
                                           --------------------------------
                                           Name:
                                           Title:




                                       ANNEX I



                                                    
Percentage Share assigned by Bank One:                 12.5%
Amount assigned by Bank One:                           $5,000,000

Percentage Share assigned by Sanwa:                    12.5%
Amount assigned by Sanwa:                              $5,000,000

Assignee's Percentage Share:                           25%
Amount of Assignee's Percentage Share:                 $10,000,000

Assignee's Commitment:                                 $10,000,000

Principal amount of Note payable to Assignee:          $10,000,000

Principal amount of Note payable to Bank One:          $15,000,000

Principal amount of Note payable to Sanwa:             $15,000,000