<PAGE>
                                                                   Exhibit 10.20


                        SOFTWARE OEM LICENSE AGREEMENT


    This Software License and OEM Agreement ("Agreement") is entered into this
19th day of May, 1997 (the "Effective Date") by and between Summit Design, Inc.,
a Delaware corporation with principal offices at 9305 SW Gemini Drive, 
Beaverton, Oregon 97008 and Test Systems Strategies, Inc., an Oregon corporation
(collectively, "SDI"), and Credence Systems Corporation, a Delaware corporation
with principal offices at 215 Fourier Avenue, Fremont, California 94539 ("CSC").

                                   RECITALS

    WHEREAS, CSC desires to purchase licenses to certain SDI software products,
and SDI desires to sell such licenses to CSC in accordance with the terms of
this Agreement; and

    WHEREAS, SDI desires to grant to CSC, and CSC desires to receive from SDI,
a non-exclusive license to bundle certain of SDI's products with certain CSC
products and to distribute such SDI products, in object code format only, with
CSC's products in accordance with the terms of this Agreement;

    NOW, THEREFORE, in consideration of the foregoing and the mutual covenants
contained herein, the parties agree as follows:


                                   Section 1
                                  DEFINITIONS

    For purposes of this Agreement the following terms shall have the meanings
set forth below:

    1.1  CSC PRODUCTS.  "CSC Products" means those CSC automatic test equipment
products which are described on SCHEDULE A attached to this Agreement, as it may
be amended from time to time by mutual agreement of the parties.

    1.2  SDI DOCUMENTATION.  "SDI Documentation" means all written or
electronic technical documentation furnished by SDI during the term of this
Agreement that relates to the VTB Software.

    1.3  VTB.  "VTB Software" means SDI's proprietary software, in 
machine-readable, compiled object code format only, as more fully described 
on SCHEDULE B, including any bug fixes, corrections, or other modifications 
hereinafter furnished to CSC by SDI in connection with the VTB Software, 
whether requested by CSC pursuant to a Maintenance Agreement between CSC and 
SDI or initiated by SDI.

    1.4  MAINTENANCE AGREEMENT.  "Maintenance Agreement" shall mean the
maintenance agreement for maintenance of the VTB Software in the form set forth
in SCHEDULE C.

<PAGE>

    1.5  END USER LICENSE AGREEMENT.  "End User License Agreement" shall mean
the end user license agreement for the VTB Software in the form set forth in
SCHEDULE E.


                                   Section 2
                        PURCHASE GRANT AND DELIVERABLES

    2.1  VTB SOFTWARE LICENSE PURCHASE.  CSC shall purchase licenses to the VTB
Software for the prices and in the quantity set forth in SCHEDULE D, in
accordance with the terms set forth in SCHEDULE D.  Each of such licenses shall
be subject to the terms of the End User License Agreement.

    2.2  MAINTENANCE PURCHASE.  CSC and SDI shall execute the Maintenance
Agreement set forth in SCHEDULE C, as of the date hereof.  CSC shall sign an
irrevocable purchase order for such Maintenance Agreement for eighteen (18)
months of maintenance for an aggregate purchase price of $2,000,000.  Payment
shall be made upon Closing (as defined in the Asset Purchase Agreement among
CSC, SDI and Test Systems, Inc.) ("Closing") by wire transfer to a bank account
designated by SDI. 

    2.3  DISTRIBUTION LICENSE.  Subject to the terms and conditions of this 
Agreement, SDI hereby grants to CSC and its affiliates, under all of SDI's 
intellectual property rights in and to the VTB Software, a worldwide, 
non-exclusive, non-transferable (except as provided in Section 10.2 below) 
license to use the VTB Software for internal purposes (provided a license for 
such use has been purchased from SDI) and distribute units of VTB Software 
purchased hereunder through its normal distribution channels, in 
machine-readable, compiled object code format only, and only when bundled 
with CSC Products or sold to customers of CSC who have purchased CSC 
Products.  For each CSC Product sold to a customer, CSC shall only issue one 
(1) VTB Software license and the VTB Software shall only be distributed to 
end users who agree to be bound by the terms of the End User License 
Agreement.  Except as expressly provided in Section 2.4 below, CSC shall have 
no right to sublicense the rights granted hereunder by SDI, provided that CSC 
and its affiliates may use subdistributors in their distribution efforts.  
CSC agrees that it shall be responsible for the compliance of its affiliates 
and subdistributors of the relevant terms of this Agreement.  CSC shall not 
distribute or market the VTB Software in any manner except as expressly 
provided in this Section 2.3.  Notwithstanding the foregoing, SDI agrees that 
it shall not distribute the VTB Software through OEM's which are automatic 
test equipment vendors to the semiconductor industry prior to January 1, 2000.

    2.4  SUBLICENSING OF VTB SOFTWARE BY CSC.

         2.4.1     RESTRICTIONS.  Each unit of VTB Software shall be
distributed by CSC with a license in the form set forth on SCHEDULE E.

         2.4.2     INDEMNITY.  CSC shall be solely responsible for, and SDI
shall have no obligation to honor, any warranties that CSC provides to its
customers with respect to the VTB Software that are in addition to, or
inconsistent with, the warranties provided by SDI in this 

                                       -2-
<PAGE>

Agreement or the End User License Agreement.  CSC shall defend any claim 
against SDI arising in connection with any such warranties to CSC's 
customers, express, implied, statutory, or otherwise, and shall pay any 
settlements or damages awarded to SDI that are based on any such warranty.

         2.4.3     INFRINGEMENTS.  CSC agrees to use reasonable commercial
efforts to enforce violations or infringements under any agreements for the VTB
Software with its customers and to inform SDI promptly of any known violation,
infringement or breach.

    2.5  DOCUMENTATION.  SDI shall provide the SDI Documentation included with
each unit of the VTB Software.

    2.6  PROPRIETARY NOTICES.  CSC shall not remove, efface or obscure any
copyright notices or other proprietary notices or legends from any SDI materials
provided hereunder.

    2.7  OWNERSHIP.  SDI shall retain all right, title and interest, including
all intellectual property rights, in and to the VTB Software and SDI
Documentation, except as otherwise provided in the Software Development
Agreement of even date herewith.

    2.8  REPORTING.  CSC shall, within thirty (30) days of the end of each
calendar quarter during the term of this Agreement, prepare a report summarizing
the number and type of copies of VTB Software distributed during such quarter.

    2.9  AUDIT.  CSC shall maintain complete and accurate accounting records,
in accordance with sound accounting practices, to support and document VTB
Software licenses distributed in connection with this Agreement.  Such records
shall be retained for a period of at least two (2) years after the year to which
they pertain. 

    2.10 VTB SOFTWARE STEERING COMMITTEE.  SDI and CSC will each appoint two
(2) representatives to a steering committee to coordinate information on the
development of the VTB Product in accordance with Section 2.1 of the Software
Development Agreement of even date herewith.


                                   Section 3
                                SDI TRADEMARKS

    CSC acknowledges that the symbols, trademarks and service marks adopted by
SDI or its suppliers to identify the VTB Software, as set forth in SCHEDULE F
attached to this Agreement (the "Trademarks"), belong to SDI and its suppliers
and that CSC shall have no rights in such Trademarks except as expressly set
forth herein.  All VTB Software distributed by CSC hereunder and all
documentation, associated brochures, packaging and advertising shall display the
Trademarks in accordance with SDI's reasonable instruction, samples of all
materials that may be distributed by CSC displaying the Trademarks shall be
submitted to SDI upon SDI's reasonable request, and the Trademarks shall be used
only in a form so approved by SDI.

                                       -3-
<PAGE>

                                   Section 4
                                     TERM

    4.1  INITIAL TERM.  This Agreement shall become effective on the Effective
Date and shall remain in effect until January 1, 2000.  This Agreement may be
renewed upon the mutual written agreement of the parties.  Each party's remedy
for breach of this Agreement shall be an action for damages or injunctive
relief; neither party shall be entitled to terminate this Agreement for any
reason.

    4.2  SURVIVAL.  The sublicenses granted to end users pursuant to
Section 2.4.1 shall survive the expiration of this Agreement pursuant to their
terms.  Also, provisions of Sections 2.7 (Ownership), 2.10 (Audit), 4 (Term),
5 (Confidentiality), 9 (Limitation of Liability) and 10 (Miscellaneous) shall
survive the expiration of this Agreement.


                                   Section 5
                                CONFIDENTIALITY

    5.1  OBLIGATIONS.  Each party (the "receiving party") acknowledges and
agrees that any business and technical information provided to the receiving
party by the other party (the "disclosing party") hereunder constitutes the
confidential and proprietary information of the disclosing party, and that the
receiving party's protection thereof is essential to this Agreement and a
condition to the receiving party's use and possession thereof.  The receiving
party shall retain in strict confidence and not disclose to any third party
(except as authorized by this Agreement) without the disclosing party's express
written consent, any and all such information.  CSC acknowledges and agrees that
the VTB Software is confidential and proprietary information of SDI.

    5.2  EXCEPTIONS.  The receiving party shall be relieved of this obligation
of confidentiality to the extent any such information:

                   (i)   was in the public domain at the time it was disclosed
    or has become in the public domain through no fault of the receiving party;

                   (ii)  the receiving party can prove was known to the
    receiving party, without restriction, at the time of disclosure as shown by
    the files of the receiving party in existence at the time of disclosure;

                   (iii) is disclosed by the receiving party with the prior
    written approval of the disclosing party;

                   (iv)  the receiving party can prove was independently
    developed by the receiving party without any use of the disclosing party's
    confidential information and by 

                                       -4-
<PAGE>

    employees or other agents of the receiving party who have not had access to 
    any of the disclosing party's confidential information; or

                   (v)   becomes known to the receiving party, without
    restriction, from a source other than the disclosing party without breach
    of this Agreement by the receiving party and otherwise not in violation of
    the disclosing party's rights.

    5.3  SOURCE CODE PROTECTIONS.  Unless as otherwise permitted under this
Agreement or another written agreement between CSC and SDI, CSC shall not under
any circumstances attempt, or knowingly permit others to attempt, to decompile,
decipher, disassemble, reverse engineer or otherwise determine the source code
for the VTB Software.

    5.4  CONFIDENTIALITY AGREEMENTS.  The receiving party, prior to permitting
access by any individual to any of the disclosing party's confidential
information, shall enter into a confidentiality agreement with each such
individual which (i) incorporates the protections and restrictions set forth
herein for the disclosing party's confidential information; (ii) provides that
the individual's obligations with respect to the disclosing party's confidential
information shall continue after termination of the individual's employment,
consulting relationship or other relationship with the receiving party; and
(iii) provides that the disclosing party is a direct and intended beneficiary of
the agreement and entitled to enforce it directly against the individual.

    5.5  NOTIFICATION OF SECURITY BREACH.  The receiving party agrees to notify
the disclosing party promptly in the event of any breach of its security under
conditions in which it would appear that the trade secrets contained in the VTB
Software were prejudiced or exposed to loss.  The receiving party shall, upon
request of the disclosing party, take all other reasonable steps necessary to
recover any compromised trade secrets disclosed to or placed in the possession
of the receiving party by virtue of this Agreement.  The cost of taking such
steps shall be borne solely by the receiving party.

    5.6  INJUNCTIVE RELIEF.  Each receiving party acknowledges that any breach
of any of its obligations with respect to confidentiality or use of the
disclosing party's confidential information hereunder is likely to cause or
threaten irreparable harm to the disclosing party, and, accordingly, the
receiving party agrees that in the event of such breach the disclosing party
shall be entitled to seek equitable relief to protect its interest therein,
including but not limited to preliminary and permanent injunctive relief, as
well as money damages.


                                   Section 6
                        REPRESENTATIONS AND WARRANTIES

    6.1  WARRANTY OF TITLE.  SDI warrants and represents to CSC that (i) CSC
shall acquire good and clear title to the VTB Software, free and clear of all
liens and encumbrances, (ii) all materials and services provided hereunder
including, without limitation, the VTB Software, are either owned or properly
licensed by SDI or are in the public domain and the use thereof by CSC, its

                                       -5-
<PAGE>

representatives, distributors or dealers will not infringe any proprietary
rights of any third party; provided, however, that SDI's obligations under
Section 7 shall be CSC's sole remedy for any breach of this warranty; and
(iii) SDI has the full power to enter into this Agreement, to carry out its
obligations under this Agreement and to grant the rights and licenses granted to
CSC in this Agreement.

    6.2  PRODUCT WARRANTY.  SDI warrants the VTB Software under the warranty
set forth in the End User License Agreement.


                                   Section 7
                                INDEMNIFICATION

    7.1  INDEMNIFICATION BY SDI.  SDI agrees to indemnify, defend and hold
harmless CSC, its affiliates, and their respective officers, directors,
employees, distributors, agents, successors and assigns from and against any and
all loss, damage, settlement or expense (including reasonable legal expenses),
as incurred, resulting from or arising out of any claims which allege that the
VTB Software or the use or sale thereof infringe upon, misappropriate or violate
any patents, copyrights, or trade secret rights or other proprietary rights of
persons, firms or entities who are not parties to this Agreement; provided that
CSC (i) promptly notifies SDI, in writing, of any notice or claim of such
alleged infringement or misappropriation involving the VTB Software of which it
becomes aware; (ii) permits SDI to control, the defense, settlement, adjustment
or compromise of any such claim; (iii) the claim does not result from
modification of the VTB Software which modification is not authorized by SDI;
and (iv) the claim does not result from the combination of the VTB Software with
software or equipment not provided by SDI if the VTB Software alone would not be
the subject of the claim.  CSC may employ counsel, at its own expense (provided
that if such counsel is necessary because SDI does not assume control, SDI will
bear such expense), to assist it with respect to any such claim.  CSC shall have
no authority to settle any claim on behalf of SDI.

    7.2  INJUNCTION.  If by reason of such infringement claim, CSC or its
customers shall be prevented or are likely to be prevented by legal means from
selling or using any VTB Software, or if, in SDI's opinion, such claim is likely
to occur, SDI will use its commercially reasonable efforts, at its expense, to: 
(i) obtain all rights required to permit the sale or use of the VTB Software by
CSC; or (ii) modify or replace such VTB Software to make then non-infringing
(and extend this indemnity thereof), provided that any such replacement or
modified VTB is functionally equivalent to the VTB Software.  If SDI is unable
to achieve either of the options set forth above within a reasonable period of
time after the issuance of the injunction, or reasonably believes that an
injunction will issue and that such options cannot be achieved within a
reasonable period of time, then neither party will sell or distribute the VTB
Software in accordance with the terms of such injunction or SDI's reasonable
instructions.  Notwithstanding the foregoing, all payments due from CSC
hereunder shall be paid whether or not the VTB Software may be used, sold or
distributed by any of the parties under such injunction or instructions of SDI. 
This Section 7 states SDI's entire obligation with respect to claims that the
VTB Software or any rights therein infringe or misappropriate the rights of any
third party.

                                       -6-
<PAGE>

                                   Section 8
                            CSC WAVEBRIDGE PRODUCTS

    CSC agrees to sell CSC Wavebridge products to SDI's customers who have
purchased VTB Software from SDI.  Upon CSC's approval, subject to SDI executing
CSC's standard Sales Representative Agreement, SDI may solicit orders from its
VTB Software customers for CSC Wavebridge products, in which case CSC shall pay
to SDI a commission of forty percent (40%) of the amount received from CSC under
such sale.


                                   Section 9
                            LIMITATION OF LIABILITY

    EXCEPT FOR THE INDEMNIFICATION OBLIGATIONS IN SECTIONS 2.4.2 AND 7, AND THE
CONFIDENTIALITY OBLIGATIONS IN SECTION 5, IN NO EVENT SHALL EITHER PARTY'S
LIABILITY ARISING OUT OF THIS AGREEMENT OR THE TERMINATION OF THIS AGREEMENT
EXCEED THE AMOUNTS PAID BY CSC TO SDI PURSUANT TO THIS AGREEMENT.  IN NO EVENT
SHALL EITHER PARTY HAVE ANY LIABILITY FOR ANY INDIRECT, INCIDENTAL, SPECIAL OR
CONSEQUENTIAL DAMAGES, HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, ARISING
OUT OF THIS AGREEMENT, INCLUDING BUT NOT LIMITED TO LOSS OF ANTICIPATED PROFITS,
EVEN IF SUCH PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.  THESE
LIMITATIONS SHALL APPLY NOTWITHSTANDING ANY FAILURE OF ESSENTIAL PURPOSE OF ANY
LIMITED REMEDY.


                                  Section 10
                                 MISCELLANEOUS

    10.1 CONFIDENTIALITY OF AGREEMENT.  Both SDI and CSC agree that the terms
and conditions of this Agreement shall be treated as confidential information
and that no reference to the terms and conditions of this Agreement or to
activities pertaining thereto can be made in any form without the prior written
consent of the other party; provided, however, that the general existence of
this Agreement shall not be treated as confidential information  and that either
party may disclose the terms and conditions of this Agreement:

                   (i)   as required by any court or other governmental body;

                   (ii)  as otherwise required by law including SDI's
    obligations under applicable securities laws;

                   (iii) to legal counsel of the parties;

                                       -7-
<PAGE>

                   (iv)  in confidence, to accountants, banks, proposed
    investors, and financing sources and their advisors;

                   (v)   in confidence, in connection with the enforcement of
    this Agreement or rights under this Agreement; or 

                   (vi)  in confidence, in connection with a merger or
    acquisition or proposed merger or acquisition, or the like.

    10.2 ASSIGNMENT.  Neither this Agreement nor any rights, licenses or
obligations hereunder, may be assigned by either party without the prior written
approval of the non-assigning party.  Notwithstanding the foregoing, either
party may assign this Agreement to a subsidiary or any acquiror of all or of
substantially all of such party's may assign this Agreement to any acquiror of
all or of substantially all of such party's equity securities, assets or
business relating to the subject matter of this Agreement, except to a direct
competitor of the other party.  As a condition to such purported assignment, the
purported assignor shall provide to the other party written confirmation prior
to such assignment of such successor's assumption of this Agreement.  Any
attempted assignment in violation of this Section shall be void and without
effect.  Subject to the foregoing, this Agreement will benefit and bind the
parties' successors and assigns.

    10.3 NOTICES.  All notices between the parties shall be in writing and
shall be deemed to have been given if personally delivered or sent by certified
or registered mail (return receipt) or telecopy to the addresses set forth as
follows, or such other address as is provided by notice as set forth herein:

    If to SDI to:            Summit Design, Inc. 
                             9305 SW Gemini Drive 
                             Beaverton, Oregon 97008
                             Attn:  Larry J. Gerhard 

    with a copy to:          Wilson Sonsini Goodrich & Rosati
                             650 Page Mill Road
                             Palo Alto, California 94304-1050
                             Attn:  Steven Bernard 

    If to CSC to:            Credence Systems Corporation
                             215 Fourier Avenue
                             Fremont, California 94539
                             Attn:  Wilmer R. Bottoms

    with a copy to:          Brobeck, Phleger & Harrison LLP
                             2200 Geng Road
                             Palo Alto, California 94303
                             Attn:  Warren Lazarow

                                       -8-
<PAGE>

    Notices shall be deemed effective upon receipt or, if delivery is not
effected by reason of some fault of the addressee, when tendered.

    10.4 RELATIONSHIP OF THE PARTIES.  The parties hereto expressly understand
and agree that each party is an independent contractor in the performance of
each and every part of this Agreement, is solely responsible for all of its
employees and agents and its labor costs and expenses arising in connection
therewith.  Neither party nor its agents or employees are the representatives of
the other party for any purpose and neither party has the power or authority as
agent, employee or any other capacity to represent, act for, bind or otherwise
create or assume any obligation on behalf of the other party for any purpose
whatsoever.

    10.5 IMPORT AND EXPORT.  Upon CSC's request, SDI shall provide all
information under its control which is necessary or useful for CSC to obtain any
export or import licenses required for CSC to ship or receive VTB Software,
including, but not limited to, certificates of origin, (NAFTA, etc.),
manufacturer's affidavits, and Buy America qualification, if applicable.  This
information is to be provided within ten (10) business days of CSC's request.

    10.6 GOVERNING LAW; FORUM SELECTION.  This Agreement shall be governed by
the laws of the State of California, without reference to its conflict of laws
principles.  All disputes arising out of this Agreement shall be subject to the
exclusive jurisdiction and venue of the California state courts of Santa Clara
County, California (or, if there is exclusive federal jurisdiction, the United
Stated District Court for the Northern District of California), and the parties
consent to the personal and exclusive jurisdiction of these courts.

    10.7 SEVERABILITY.  Any term or provision of this Agreement held to be
illegal or unenforceable shall, if possible, be interpreted so as to be
construed as valid, but in any event the validity or enforceability of the
remainder hereof shall not be affected.

    10.8 EXPORT REGULATIONS.  CSC understands that SDI is subject to regulation
by agencies of the U.S. government, including the U.S. Department of Commerce,
which prohibit export or diversion of certain technical products to certain
countries.  CSC warrants that it will comply in all respects with the export and
re-export restrictions applicable to the technology and documentation licensed
hereunder.

    10.9 WAIVER.  The waiver of, or failure to enforce, any breach or default
hereunder shall not constitute the waiver of any other or subsequent breach or
default.

    10.10     ENTIRE AGREEMENT.  This Agreement, along with the Schedules
attached hereto which are incorporated herein by reference, sets forth the
entire Agreement between the parties and supersedes any and all prior proposals,
agreements, and representations between them, whether written or oral.  This
Agreement may be changed only by mutual agreement of the parties in writing.

                 [Remainder of page intentionally left blank.]

                                       -9-
<PAGE>


     IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be 
signed by duly authorized officers or representatives as of the Effective 
Date.

SUMMIT DESIGN, INC.                    CREDENCE SYSTEMS CORPORATION


By: /s/ Larry J. Gerhard               By: /s/  Richard Y. Okumoto  
   -------------------------------        --------------------------------------

Name: Larry J. Gerhard                 Name: Richard Y. Okumoto        
     -----------------------------          ------------------------------------

Title: President, CEO                  Title: Executive Vice President & CFO
      ----------------------------           -----------------------------------

Date: 5/19/97                          Date: 5/19/97                       
     -----------------------------          ------------------------------------

                                       -10-
<PAGE>


                                  SCHEDULE A

                                 CSC PRODUCTS

VISTA/DUO SERIES TESTERS

SC SERIES TESTERS

<PAGE>
                                  SCHEDULE B

                                 VTB SOFTWARE

    
VISUAL TESTBENCH COMPONENTS

Visual Testbench consists of modified Visual HDL for Verilog and VHDL, Visual
Testbench harness code, Visual HDL simulation interface, various internal TDS
routines, WDB input/output routines and Visual Testbench on-line documentation. 
For customer delivery these source code modules are compiled to a single Visual
Testbench binary executable module

A Testbench  is created using the Visual HDL Flow chart editor, Block diagram
editor and  Waveform/Timing diagram  editor.   The Testbench is connected to the
simulated circuit using the Visual HDL Block Diagram editor and the Visual
Testbench Launch editor.

The Testbench harness is compiled with the customer's simulator and design as to
stimulate and examine the circuit under investigation.  The Testbench harness
reads and writes TSSI WDB databases through binary linkable library functions.

The examples include Visual HDL databases and Verilog or VHDL codes sufficient
to demonstrate basic and advanced product operation.  The examples are
operational and will produce legitimate WDB output.

DOCUMENTATION
Visual Testbench documentation consists of a binary file in Framemaker mif
format describing theory of operation, external controls, and function call
interface of the product.  The mif file is interpreted by a view for run time
viewing of the test.

<PAGE>

                                  SCHEDULE C

                             MAINTENANCE AGREEMENT

    This Maintenance Agreement ("Agreement") is entered into between Summit 
    Design, Inc., a Delaware Corporation ("Summit") and Credence Systems Corp. 
    ("CSC") for the products described in the Software OEM License Agreement 
    between Summit and CSC ("the Software"), which is incorporated herein by 
    this reference.

    IN CONSIDERATION OF THE MUTUAL COVENANTS SET FORTH HEREIN, THE PARTIES 
    AGREE AS FOLLOWS:

1.  FEES

    During the term of this Agreement and any renewal term thereof, Customer 
    shall pay a  maintenance fee for each term ("the Maintenance Fee") as 
    determined by the parties.  The Maintenance Fee is due upon the execution of
    this Agreement, or the expiration of any applicable warranty period for the 
    above-described Software ("Software"), whichever last occurs.  

2.  TERM

    The term of this Agreement shall be eighteen (18) months.  Thereafter, this
    Agreement can be renewed for successive annual terms within the ninety (90) 
    day period immediately prior to the expiration of the current term or any 
    renewal term.  After the eighteen months, this Agreement may be terminated 
    by either party upon thirty (30) days' written notice:  however, in the 
    event of termination by Customer, Summit shall not be obligated to refund 
    any advance maintenance fees, and any fees due and payable shall remain due 
    and payable without adjustment for early termination.

3.  CUSTOMER OBLIGATIONS

    To facilitate Summit's performance under this Agreement, Customer shall: 

    3.1  Promptly notify Summit in writing or by telephone of the need for
         maintenance services, the Software License Agreement Number, the Serial
         Numbers and Release Numbers of the Software, the location of the 
         Software site number, a description of the CPU on which the Software is
         being used, and the nature of the problem.

    3.2  Cooperate with Summit as reasonably necessary to identify the nature 
         and cause of the problem.

    3.3  Allow Summit access to Customers' hardware, products, systems and
         information (including confidential information), as may be reasonably 
         necessary to facilitate Summit's identification of the nature, cause 
         and potential remedy of the problem, all subject to Customers' security
         and safety rules.

<PAGE>

4.  SUMMIT'S OBLIGATIONS

    4.1  During the term of the Agreement and any renewal term thereof, Summit 
         shall respond to CSC requirements for telephone technical support and 
         bug fix requests.


5.  SPECIAL TERMS AND CONDITIONS

    5.1. This maintenance agreement does not provide for upgrade releases. 

    5.2  This Agreement shall apply to the Software in its standard form, and 
         shall not apply to custom enhancements and modifications.  Any 
         requested service on custom enhancements and modifications shall be 
         charged to Customer at Summit Design's standard service rates then in 
         effect.

    5.3  This Agreement shall apply only to the original release of the 
         Software.

    5.4  Although Summit will exert reasonable efforts to provide prompt 
         service, Summit is not liable for damages resulting from delay in the 
         provision of service caused by circumstances beyond reasonable control.

    5.5  Summit's maintenance obligations under this Agreement do not include; 
         (a) services connected with system reconfiguration or relocation, (b) 
         service resulting from neglect, misuse or accidental damages to the 
         Software, (c) service resulting from modifications or repairs of the 
         Software without Summit's authority, (d) service resulting from the 
         failure of Customer to provide and maintain a suitable installation 
         environment, (e) service resulting from the use of the Software for 
         other than the purposes for which it was designed, (f) the provision 
         of supplies, accessories, or media.

<PAGE>


                                  SCHEDULE D

                            LICENSE FEE AND PAYMENT


Per Copy License Fee:   
      US $***

Payment and Delivery Schedule:

    CSC shall issue to SDI an irrevocable purchase order for *** VTB Software 
licenses for the amount of $16,000,000 on the Closing.  Also on the Closing, 
CSC shall establish an irrevocable letter of credit with a nationally 
recognized financial institution reasonably acceptable to SDI, in the amount 
of $16,000,000 for payment of such *** VTB Software licenses.  SDI shall have 
the right to ship up to the number of licenses corresponding to the maximum 
payments set forth below and SDI shall receive the payment calculated at $*** 
per license, drawn from the letter of credit upon each such shipment.  If SDI 
does not ship the permitted maximum during a quarter, the shortfall will be 
carried forward to the next quarter's maximum amount.

        Year and
        Calendar                           Quarterly                    Annual
         Quarter                            Maximum                    Maximum
       ----------                          ---------                  ---------
       1997 Q1
       1997 Q2
       1997 Q3                             $  ***
       1997 Q4                             $  ***
       1997 Total                                                     $   ***
       1998 Q1                             $  ***
       1998 Q2                             $  ***
       1998 Q3                             $  ***
       1998 Q4                             $  ***
       1998 Total                                                     $   ***
       1999 Q1                             $  ***
       1999 Q2                             $  ***
       1999 Q3                             $  ***
       1999 Q4                             $  ***
       1999 Total                                                     $   ***

    Shipment of VTB Software shall be made by the fifteenth day of the first 
month for each quarter and payment shall be drawn from the letter of credit 
on the same day.  VTB Software will be shipped to CSC via overnight courier.  

*    Certain information on this page has been omitted and filed separately 
     with the Commission.  Confidential treatment has been requested with 
     respect to the omitted portions.

<PAGE>
                                  SCHEDULE E

                          END USER LICENSE AGREEMENT

This is a legal Agreement between you, the end user, and Summit Design, Inc.  
By opening this sealed media package and/or by using the Software, you are 
agreeing to be bound by the terms of this Agreement.

GRANT OF LICENSE.  Summit Design, Inc. ("Summit") grants you the right to use 
one (1) copy of the enclosed Summit software program and accompanying 
documentation (together with any upgrades supplied by Summit, the "Software") 
according to the conditions specified below.  Usage area to be less than one 
kilometer in radius and subject to the terms and conditions of this 
Agreement. All rights not expressly granted herein are reserved by Summit, 
its suppliers, licensors, or successors.

YOU MAY:
a.  Install the Software and its License Manager (FlexLM) on only one
    computer or workstation;
b.  make no more than one (1) copy of the Software in machine readable form,
    solely for back-up purposes, provided that you reproduce all proprietary 
    notices on the copy; and
c.  physically transfer the Software from one computer to another, provided
    that the Software is used on only one computer at a time, and within a usage
    area to be less than one kilometer in radius.

YOU MAY NOT:
a.  Use the Software on more than one computer or workstation at a time;
b.  modify, translate, reverse engineer, decompile, disassemble, create
    derivative works based on, or copy (except to create the back-up copy) the
    Software;
c.  rent, lend, transfer, distribute, or grant any rights in the Software in
    any form to any person without the written consent of Summit;
d.  remove any proprietary notices, labels, or marks from the Software; or
e.  operate the Software on networks where two client nodes using Summit
    products of this type are greater than two (2) kilometers from each other 
    (WAN).

UPGRADE PRODUCTS.  Any upgrades to the Software may only be used in conjunction
with the prior version of the Software.

LIMITED WARRANTY AND DISCLAIMER.  Summit warrants that for a period of ninety
(90) days from the date of sale of the Software to you, the media on which the
Software is furnished will, under normal use, be free from defects in materials
and workmanship.  Summit's entire liability and your exclusive remedy under this
warranty (which is subject to you returning the Software to Summit) will be, at
Summit's option, to replace the media or to refund the purchase price and
terminate this Agreement.  Except for these express limited warranties, Summit
makes, and you receive, no warranties or conditions, express, implied,
statutory, or otherwise, and Summit specifically disclaims any implied
warranties of merchantability, noninfringement and fitness for a particular
purpose.  Summit does not warrant that the Software will meet your requirements
or that the operation of the Software will be uninterrupted or error free.  You
assume the responsibility for the selection of your requirements, software, and
hardware to achieve your intended results; for installation; for use; and that
the operations of the Software will be uninterrupted or error free.  Some States
do not allow the exclusion of implied warranties so that the above exclusions
may not apply to you.  This warranty gives you specific legal rights.  You may
also have other rights which vary from State to State.

PROPRIETARY RIGHTS.  This license is not a sale.  Title and copyrights to the
Software and accompanying documentation, including the enclosed copies and any
copy made by you, remain with Summit or its suppliers, licensors, or successors.

LIMITATION OF LIABILITY.  Summit's liability arising out of this Agreement shall
not exceed the amounts paid by you to obtain the Software.  In no event will
Summit be liable for any loss of data, lost opportunity of profits, cost of
cover, or special, incidental, consequential, or indirect damages arising from
the use of the Software in this Agreement, however caused and on any theory of
liability.  These limitations will apply even if Summit or an authorized dealer
has been advised of the possibility of such damage, and notwithstanding any
failure of essential purpose of any limited remedy.  You acknowledge that the
amount paid for the Software reflects this allocation of risk.  Some States do
not allow the limitation or exclusion of liability for incidental or
consequential damages, so the above limitation or exclusion may not apply to
you.


<PAGE>

EXPORT RESTRICTIONS.  You agree that you will not export or re-export the
Software in any form without the appropriate United States and foreign
government licenses, and Summit written approval.  Your failure to comply with
this provision is a material breach of this contract.  If you need advice on
such export laws and regulations, you should contact the U.S. Department of
Commerce, Export Division, Washington, DC 20230, USA , for clarification.

TERMINATION.  This Agreement is effective until terminated.  You may terminate
this Agreement at any time by removing from your system and destroying all
copies of the Software and the accompanying documentation.  Unauthorized copying
of the software or the accompanying documentation or otherwise failing to comply
with the terms and conditions of this Agreement will result in automatic
termination of this Agreement and will make available to Summit other legal
remedies.  Upon termination of this Agreement, the license granted herein will
terminate and you must immediately destroy the Software and accompanying
documentation, and all back-up copies thereof.

U.S. GOVERNMENT USE.  The Software and accompanying documentation are deemed to
be "commercial computer software" and "commercial computer software
documentation," respectively, pursuant to DFAR Section 227.7202 and FAR Section
12.212, as applicable.  Any use, modification, reproduction, release,
performing, displaying or disclosing of the Software and accompanying
documentation by the U. S. Government shall be governed solely by the terms of
this Agreement and shall be prohibited except to the extent expressly permitted
by the terms of this Agreement.

MISCELLANEOUS.  This is the entire Agreement between the parties relating to 
the subject matter hereof and no waiver or modification of the Agreement 
shall be valid unless signed by each party.  The waiver of a breach of any 
term hereof shall in no way be construed as a waiver of any other term or 
breach hereof.  If any provision of this Agreement shall be held by a court 
of competent jurisdiction to be contrary to law, the remaining provisions of 
this Agreement shall remain in full force and effect.  This Agreement is 
governed by the laws of the State of Oregon without reference to conflict of 
laws principles.  All disputes arising out of this Agreement shall be subject 
to the exclusive jurisdiction of the state and federal courts located in 
Multnomah County, Oregon, and the parties agree and submit to the personal 
and exclusive jurisdiction and venue of these courts.  Should you have any 
question about this Agreement, or if you desire to contract Summit Design, 
Inc., please write: Summit Design, Inc., 9305 S.W. Gemini Drive, Beaverton, 
Oregon 97008 USA (503-643-9281).

BEFORE OPENING THIS ENVELOPE, carefully read the License Agreement on the
reverse side of this envelope.  By opening this envelope and/or by using the
software contained herein, you are agreeing to be bound by the terms of the
License Agreement.

<PAGE>
                                  SCHEDULE F

                                  TRADEMARKS

    
Visual Test             Serial No.   75/002, 501      US
Visual Test             11216-TM1003                  US
Visual Testbench        11216-TM1034                  International Class 9