<PAGE>
 
                                                                   Exhibit 10.16

CONTRACT OF PURCHASE AND SALE


THIS CONTRACT OF PURCHASE AND SALE ("Agreement") is made this ___ day of April,
1997, and constitutes an agreement by Objective Systems Integrators, Inc. or its
assigns ("Buyer"), to purchase from the John A. Sobrato 1979 Trust, a California
limited partnership ("Seller"), the real property of approximately 14 acres
located within Lake Forest Business Park in Folsom, California, together with
all improvements, licenses, rights and easements attached to, appurtenant to,
located on or used in connection with such real property (collectively, the
"Property"), legally defined as follows:

Lot 3, as shown on the official Plat of Lake Forest Industrial Park, recorded in
the office of the County Recorder of Sacramento County, on October 22, 1980, APN
071-0530-003.

The Property shall be purchased on the following terms and conditions:

        1.      Purchase and Sale. Seller agrees to sell to Buyer, and Buyer
agrees to purchase from Seller, the Property upon the terms and conditions
herein set forth.

        2.      Purchase Price. The purchase price ("Purchase Price") for the
Property below shall be Two Million Five Hundred Ninety One Thousand Eight
Hundred Twenty and No/100 Dollars ($2,591,820.00), subject to adjustment as
provided in this paragraph. The foregoing Purchase Price is based on the
assumption that the area of the Property is exactly fourteen (14) acres. On or
before the Revocation Date (as defined herein), Buyer shall have the right to
cause to be prepared and delivered to Seller a survey of the Property prepared
by a licensed civil engineer or licensed land surveyor containing such
engineer's or surveyor's certification of the area of the Property contained
within the boundary lines of the Property (including landscape, utility and
other easements but excluding any area which is within the right of way of any
existing public street or highway). Such survey shall establish the area of the
Property, absent manifest error. If the area of the Property established by such
survey is more or less than fourteen (14) acres, the Purchase Price shall be
adjusted to that amount which is equal to the product obtained by multiplying
Four Dollars and Twenty-Five Cents ($4.25) per square foot by the area of the
Property expressed in square feet.

        3.      Payment of Purchase Price. The Purchase Price for the Property
shall be payable as follows:

                A.      Deposit. The date upon which an original of this
Agreement is executed by Seller and delivered to Buyer shall be deemed the
"Effective Date". Within three (3) days following the Effective Date, Buyer
shall deliver to Santa Clara Land Title Insurance Company ("Title Company") cash
or certified funds in the amount of Fifty Thousand and No/100 Dollars
($50,000.00) ("Initial Cash Deposit"). The Initial Cash Deposit shall be
returnable upon demand by Buyer until 5:00 p.m. (PST) on the date that is sixty
(60) days after the Effective Date ("Revocation Date"). If Buyer does not make
such demand on or before the Revocation Date, Buyer shall increase the Initial
Cash Deposit to a total of One Hundred Thousand and No/100 Dollars ($100,000.00)
("Total Cash Deposit"). Except as otherwise provided in the Agreement, after the
Revocation Date the Initial and Total Cash Deposits shall be either (i) paid to
Seller as part of the Purchase Price at Close of Escrow, (ii) returned to Buyer
in the event this Agreement is terminated because of the failure of a condition
for the benefit of Buyer or because of a material default by Seller, or (iii)
paid to Seller as liquidated damages pursuant to paragraph 16A hereof in the
event this Agreement is terminated because of a default by Buyer of its
obligation to purchase the Property. The Total Cash Deposit shall be deposited
by Escrow Holder in an interest bearing account and interest shall be payable to
Buyer's account and shall be applied and credited toward payment of the Purchase
Price. In the event of Buyer's default hereunder, Escrow Holder is authorized to
deliver to Seller the Total Cash Deposit, including accrued interest upon demand
from Seller.
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                B.      Cash Balance. Buyer shall deliver additional cash or
certified funds (the "Cash Balance") which, when added to the Total Cash
Deposit, shall equal closing ("Closing"), which Closing shall occur on or before
ninety (90) days following the Effective Date ("Scheduled Closing Date").

        4.      Buyer's Conditions Precedent to Close of Escrow. Buyer's
obligation to purchase the Property pursuant to this Agreement is subject to the
following conditions and contingencies:

                A.      Approval of Preliminary Title Report. Buyer shall have
fourteen (14) business days from Seller's delivery of a current preliminary
title report on the Property issued by the Title Company (including copies of
all underlying exceptions to title referenced in such title report) to notify
Seller in writing ("Buyer's Title Notice") of any objections or conditional
approval of any matters shown in the Report. The failure of Buyer to give
Buyer's Title Notice within the 14 day period shall be deemed to constitute
Buyer's approval of condition of title to the property. If Buyer disapproves or
conditionally approves any matter of title shown, in the report, then Seller
may, but is not obligated to, within 10 days after its receipt of Buyer's Title
Notice, elect to eliminate or ameliorate to Buyer's satisfaction, the
disapproved or conditionally approved title matters, by giving Buyer written
notice of those disapproved or conditionally approved title matter's ("Seller's
Title Notice"), if any, that Seller agrees to eliminate or ameliorate, by the
closing date, provided that Seller shall have no obligation to pay any
consideration or incur any liability in order to eliminate or ameliorate such
disapproved title matters. If Seller does not elect to eliminate or ameliorate
disapproved or conditionally approved title matters, or if Buyer reasonably
disapproves Seller's Title Notice, or if Seller fails to timely deliver Seller's
Title notice, then Buyer shall have the right, upon delivery to Seller and
Escrow Holder (on or before five days following the expiration of Seller's
election period) of a written notice to either: (i) waive its prior disapproval
in which event said disapproved matters shall be deemed approved; or (ii)
terminate this Agreement and the Escrow created pursuant hereto and receive a
refund of the Initial Cash Deposit. Failure to take either one of these actions
described above shall be deemed Buyers election to take the action described in
(i) above. If the Title Company issues any supplement to the preliminary title
report for the Property delivered to Buyer which supplement identifies any new
matters not contained in the first preliminary title report, then Buyer shall
have the right to deliver written notice of its objection to the same, in the
manner described above, and Seller shall have the same right to eliminate or
ameliorate such new title matter, all in accordance with the same procedure, and
the same time frames, as stated above, but measured from the date Buyer receives
such supplement to the preliminary title report (and Close of Escrow shall be
extended to the extent necessary to allow the procedures described in this
subparagraph 4(A) to be completed with respect to any such new matter described
by an such supplement to the first preliminary title report.) Notwithstanding
anything contained herein, Buyer shall have no obligation to approve, and seller
shall eliminate prior to Close of Escrow as exceptions to title, any mortgage,
deed of trust, judgment lien, tax lien, mechanic's lien, or other encumbrance
securing the payment of money.

                B.      Inspection of Property. Buyer and its consultants shall
have the right to enter the Property only during normal business hours upon
reasonable notice to Seller for the purpose of inspecting all aspects of the
Property to determine its present condition including the right to conduct
reasonable soils tests, environmental assessment work, engineering studies and
surveys. Buyer shall indemnify and hold Seller and the property harmless from
any damage, liability, expense, claim, cost, lien, action or judgment including
the cost of Seller's reasonable attorney's fees for or related to labor or
services performed or materials furnished to or for Buyer or for personal
injury, death or property damage arising out of or resulting from actions taken
by Buyer or any of its employees, agents or independent contractors during any
entries upon the Property. Buyer shall restore the Property to good, safe, and
clean condition and repair after concluding such tests and activities. Buyer
further agrees to reimburse Seller for all physical damage to the Property
caused by such testing if Buyer does not purchase the property.

                C.      Review of Documents. Seller shall, within five (5)
business days following the Effective Date, deliver to Buyer for Buyer's review
and approval (collectively "Property Documents"): (i) a copy of the most recent
tax bills for the Property; and (ii) copies of any soil and groundwater
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contamination reports, and any other environmental audit report to the extent
such reports have been prepared and are within Seller's possession or control;
and (iii) copies of all documents in Seller's possession or control which relate
to the ownership, development, or condition of the Property (excluding documents
recorded in the public records.) Buyer may order such environmental site
assessments as Buyer may desire and Seller will cooperate to enable the reports
to be made. Buyer shall pay the costs of such reports and agrees to reimburse
Seller for any physical damage to the Property caused by such testing. In the
event Buyer discovers any substance or material that has been determined by any
state, federal or local authority or regulatory body to be capable of posing a
risk of injury to health, safety, and/or property ("Hazardous Materials") on the
Property at any time prior to Closing, or if Buyer discovers that contamination
of property adjacent to the Property poses a material threat of contaminating
the Property by migration, Buyer shall have the option to terminate this
agreement by written notice and shall receive a full refund of the Total Cash
Deposit with accrued interest thereon.

                D.      Independent Judgment. make its own determination as to
the scope of the due diligence investigation of the Property within the time
period as provided for in this Section 4. In making such determination, Buyer
acknowledges and agrees that Buyer has not and shall not rely on any of the
studies, reports, documents, work product, maps or other materials or
information pertaining to the soil and ground water contamination or other
environmental contamination reports, if any, delivered or made available to
Buyer from Seller, Seller's agents or representatives (collectively, "Seller's
Reports"). It is specifically understood and agreed that, to the extent that
Seller delivers (or makes available) to Buyer any Seller's Reports, Seller does
so strictly as an accommodation to Buyer. In the event Buyer does not purchase
the Property, Buyer shall use reasonable efforts to keep all information
obtained by Buyer relating to the Property (which information is referred to
herein as "Confidential Information") confidential and shall not disclose any
Confidential Information to a third party without the consent of Seller. Buyer's
obligation to use reasonable efforts shall include, but not be limited to the
following: (i) notifying its employees (but not any agents or contractors of
Buyer) of the confidential nature of the Confidential Information and of the
agreement contained in the immediately preceding sentence, and (ii) not
disclosing the Confidential Information to any newspaper, journal, magazine or
other news media, or any other person. Nothing in the paragraph shall be deemed
to preclude Buyer from disclosing any information (a) that has been released
into the public domain, or (b) pursuant to law or judicial process.
 
                E.      Buyer's Right to Terminate. In the event Buyer, in its
sole and absolute discretion, does not desire to purchase the Property for any
reason, Buyer shall have until 5:00 p.m. (PST) on the Revocation Date to elect
to terminate this Agreement and receive a full refund of its Initial Cash
Deposit plus any interest earned on the Initial Cash Deposit. Buyer shall
exercise such right to terminate, if at all, by delivering to Seller a written
notice to terminate which notice shall be received by Seller on or before the
Revocation Date. In the event Buyer does not timely notify Seller of its
intention to terminate this Agreement on or before the Revocation Date, this
Agreement shall remain in full force and the parties shall proceed to closing in
accordance with the terms of the Agreement. In the event Seller fails to deliver
any of the Property Documents to Buyer within five business (5) days following
the Effective Date, the Revocation Date and Scheduled Closing Date shall
automatically be extended by the number of days equal to the number of days
delay in delivering all Property Documents beyond such five (5) business-day
period.

        5.      Policy of Title Insurance on Real Property. Seller agrees to
convey to Buyer (or its assignee), by grant deed, good, marketable and insurable
title to the Property, subject only to the title exceptions approved or deemed
approved by Buyer pursuant to Section 4(A) above ("Permitted Exceptions"). For
purposed of this Agreement, good, marketable and insurance title shall mean such
title as evidenced by the Title Company issuing to Buyer at the Closing a CLTA
Owner's Policy of Title Insurance in form and substance reasonably satisfactory
to Buyer (the "Policy"), insuring Buyer or its assignee in the amount of the
Purchase Price that title to the Property is vested in Buyer on the Closing,
subject only to the exceptions to title approved by Buyer under Section 4(A).
Buyer may elect to obtain ALTA title insurance coverage, rather than the CLTA
Owner's Policy described above, subject to the
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following conditions: (I) provision of such coverage shall not delay the close
of escrow; (ii) Buyer shall pay all additional costs of obtaining such coverage,
including the cost of any required survey; (iii) Buyer shall obtain and deliver
to the Title Company any required survey and order the Title Company's
inspection of the Property in sufficient time in advance so that any additional
exceptions resulting from the Title Company's review of the survey and
inspection will be reviewed and approved or disapproved by Buyer in the manner
described in subparagraph 4A hereof, and (iv) Seller shall have the option (but
not the obligation ) to cure any such disapproved exceptions as described in
subparagraph 4A hereof;

        6.      Covenants Regarding Closing. 

                A.      Seller's Deliveries to Title Company. Seller agrees to
deliver to Title Company on or prior to the Closing, (i) a Grant Deed duly
executed and acknowledged by Seller, conveying the Property to Buyer (or its
assignee); (ii) a federal non-foreign person affidavit (FIRPTA Affidavit); (iii)
a California Form 590 withholding exemption certificate; and (iv) Seller's share
of costs and prorations for closing required to be paid by Seller hereunder.

                B.      Other Covenants of Seller. Prior to Closing, Seller
covenants and agrees that it will: (i) keep in full force all insurance policies
affecting the Property; (ii) keep the Property in its present condition; and
(iii) keep the Property free and clear from any and all claims, liens, demands
arising out of any work performed or materials furnished with respect to the
Property.

                C.      Buyer's Deliveries to Title Company. Buyer agrees to
deliver to Title Company, on or prior to the Closing, for disbursement as
provided in the Agreement (i) the Cash Balance, together with Buyer's share of
costs and prorations required to be paid buy Buyer under this Agreement; and
(ii) evidence satisfactory to Title Company that Buyer is qualified to hold and
own real estate in the State of California.

        7.      Escrow Opening and Closing Costs. Upon Effective Date, an escrow
shall be opened by the Parties at Title Company for the Closing which shall
occur on or before the Scheduled Closing Date. In the event Buyer elects to
close escrow before the Scheduled Closing Date, Buyer shall give written notice
to Seller of such election at least five (5) business days preceding the elected
earlier date for Closing and the closing shall occur on such earlier date. Buyer
and Seller agree to execute such documents as the Title Company may reasonable
require to open escrow and close the transaction contemplate by this Agreement.

        8.      Costs and Expenses. Seller shall pay the premium for the Policy,
the escrow fee, and one-half (1/2) of the documentary transfer taxes and city
transfer taxes payable in connection with the recordation of the Grant Deed, and
all such other closing costs related to the conveyance of the Property
customarily paid by sellers in Sacramento County. Buyer shall pay one-half (1/2)
of the documentary transfer taxes and city transfer taxes payable in connection
with the recordation of the Grant Deed and all such other closing costs related
to the conveyance of the Property customarily paid by Buyer in Sacramento County
and shall assume all assessments of record. Buyer shall pay legal fees and fees
of other consultants retained by Buyer and Seller shall be responsible for the
payment of legal fees and fees of other consultants retained by Seller. Real
estate taxes, rents, utilities and other expenses shall be prorated as of the
date of the Closing.

        9.      Disbursements and Other Actions At the Closing. When, and only
when the Title Company (i) has received all the funds, documents and items
described in Section 6, and (ii) is in a position to issue the Policy to Buyer
in the form described in Section 5 above, then the Title Company is authorized
to take the following actions at or immediately after the Closing:

                A.      Recording. Cause the Grant Deed, and any other documents
which the parties may mutually direct, to be recorded in the Official Records of
Sacramento County;
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                B.      Funds. All items chargeable to the account of Seller
pursuant hereto, including the payment for recording and escrow fees shall be
deducted from the Purchase Price deposited by Buyer as follows and the remaining
balance shall be paid to Seller or as Seller may direct;

                C.      Disbursement of Documents to Buyer. Disburse to Buyer
the Bill of Sale and Assignment of Rights, and, after recording, the Grant Deed;
and

                D.      Issuance of Policy. Cause the Title Policy to be issued
and delivered to Buyer in accordance with Section 5.

        10.     Seller's Representations and Warranties. The following
constitute representations and warranties of Seller which are true and accurate
as of the date hereof and which shall be true and correct as of the Closing.

                A.      Seller has the legal power, right and authority to enter
into this Agreement and to consummate the transactions contemplated hereby and
no other action by Seller is requisite to the valid and binding execution,
delivery and performance of this Agreement.
        
                B.      This Agreement and all documents required hereby to be
executed by Seller shall be valid, legally binding obligations of and
enforceable against Seller in accordance with their terms.

                C.      Neither the execution and delivery of this Agreement,
nor the assumption of the obligations herein set forth, nor the consummation of
the transactions herein contemplated will conflict with or result in a breach of
any conditions or provisions of, or constitute a default under, any contract,
agreement, or other obligation to which Seller is a party.

                D.      Seller has no knowledge, except as otherwise disclosed
to Buyer in this Agreement or in writing delivered prior to close of escrow, of
the existence or prior existence on the Property of any Hazardous Material. To
Seller's knowledge, no summons, citation, directive, order or other
communication has been issued to Seller arising out of or relating to the
presence of Hazardous Materials on the Property.

                E.      Seller has not received written notice of any pending or
planned public improvements or assessments that involve or will involve the
Property or result in any charge or lien against the Property.

                F.      Seller has received no written notice of, and has no
knowledge of, (I) any pending or threatened action or proceedings relating to
the Property or, if such claim relates to the Property, against Seller, or (ii)
any pending or threatened condemnation or zoning proceeding affecting the
Property.

                G.      To Seller's knowledge, title to the Property is not
subject to any liens, encumbrances, easements, licenses, leases or other
exceptions to fee title except those which are described by the preliminary
title report received by Buyer.

                H.      To Seller's knowledge, there is no agreement or other
undertaking with any person or governmental entity that limits the use or
development of the Property or the availability of all necessary utilities for
the development of the Property, nor is there any state of facts or condition
affecting the Property which would materially and adversely affect Seller's
ability to develop the Property, except as set forth in the zoning, building
codes and other laws of general applicability to the Property.

        11.     Buyer's Representations. The following constitute
representations and warranties of Buyer which are true and accurate as of the
date hereof and which shall be true and correct as of the Closing:
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                A.      Buyer has the legal power, right and authority to enter
into this Agreement and to consummate the transactions contemplated hereby and
no other action by Buyer is requisite to the valid and binding execution,
delivery and performance of the Agreement, except as expressly set forth herein.

                B.      This Agreement and all documents requires hereby to be
executed by Buyer shall be valid, legally binding obligations of and enforceable
against Buyer in accordance with their terms.

                C.      Neither the execution and delivery of this Agreement,
nor the assumption of the obligations herein set forth, nor the consummation of
the transactions herein contemplated will conflict with or result in a breach of
any conditions or provisions of, or constitute a default under, any contract,
agreement, or other obligation to which Seller is a party.

        12.     Sold in "As Is" Condition. Buyer is acquiring the Property
strictly "AS-IS" and "WITH ALL FAULTS", in the condition of the Building that
exists on the Revocation Date and assumes the risk that adverse physical
conditions may not have been revealed by its investigation. Except with respect
to those express covenants, representations and warranties made in Section 10,
Buyer acknowledges and agrees that neither Seller or Seller's agents or
representatives, have made any covenants, representations or warranties of any
kind or nature whatsoever, either express or implied, oral or written, with
respect to (i) the physical condition of the Property, (ii) the development
potential of the Property (iii) any Seller Reports furnished pursuant to Section
4, or (iv) any other matters related thereto or to this Agreement. Except for
those express representations made in Section 10 by Seller, Buyer further agrees
that it is not relying on any covenant, representation or warranty, express or
implied, oral or written, with respect to (i) the physical condition of the
Property, (ii) the development potential of the Property (iii) any Seller
Reports furnished pursuant to Section 4, or (iv) any other matters related
thereto or to this Agreement.

        13.      Condemnation and Destruction. If, prior to the Closing, all or
any of the Property is destroyed by fire or other cause or if the property is
made the subject of eminent domain proceedings, Buyer may, at its option, elect
to (i) terminate the Agreement, in which event each party shall pay one-half the
costs of any cancellation fee charged by Title Company, or (ii) continue this
Agreement in effect and proceed to close in accordance with this Agreement. If
Buyer elects to close, Buyer shall be entitled to receive and keep any
compensation, awards, insurance proceeds or other relief and Buyer and Seller
shall proceed with the Closing without modification of the terms of the
Agreement and without any reduction in the Purchase Price. If Buyer does not
elect to close, Buyer shall receive a refund of the Initial Cash Deposit or
Total Cash Deposit plus any accrued interest. Upon the request of Buyer, Seller
agrees to execute such reasonable documents and take such actions as may be
reasonably necessary for Buyer to receive the insurance proceeds and/or
condemnations awards described in this Section 13.

        14.     Notices. All notices of other communications required or
permitted hereunder shall be in writing, and shall be personally delivered or
sent by registered or certified mail, postage prepaid, return receipt requested,
and shall be deemed given upon delivery (if personally delivered) or forty eight
(48) hours after deposit in the United States Mail (if mailed):
          
To Buyer:                       To Seller:              To Title Company:
Objective Integrators, Inc.     Sobrato Development     Santa Clara Land Title
Blue Ravine Road                10600 N. DeAnza Blvd.   701 Miller Street
Folsom, CA  95630               Cupertino, CA  95014    San Jose, CA  95110     
Attn:  Phil Cardman             Attn:  Phil Taylor      Attn: Linda Tugade
Notice of change of address shall be given to the other party by written notice
in accordance with this Section 14.

        15.     Brokers. Each party represents and warrants to the other that it
has engaged no broker, agent, or finder, licensed or otherwise, except CB
Commercial Real Estate and Colliers Ileff Thorn whose commission shall be paid
by Seller provided escrow closes in accordance with Section 9 above. In such
<PAGE>
 
event, the amount of commission paid to CB Commercial shall be equal to 3% of
the Purchase Price and the amount of commission paid to Colliers Ileff Thorn
shall be equal to 2% of the Purchase Price. In the event that escrow fails to
close for any reason, no commission shall be payable (including as a result of a
default by Seller or Buyer, the failure of a condition, or rescission), and
under no circumstances shall Buyer have any obligation to pay any commission or
damages for failing to close to any broker engaged either by Seller or Buyer in
connection with this transaction. In the event of any additional claim for a
finder's fee or commission in connection with the negotiation, execution, or
consummation of this transaction based upon either party's representation, or
agreement, such party shall indemnify, hold harmless, and defend the other party
from and against such claim or liability including without limitation reasonable
attorney's fees and court costs.

        16.     Legal and Equitable Enforcement of this Agreement:

                A.      Default by Buyer. IN THE EVENT THE CLOSING DOES NOT
OCCUR AS HEREIN PROVIDED BY REASON OF ANY DEFAULT OF BUYER, BUYER AND SELLER
AGREE THAT IT WOULD BE IMPRACTICAL AND EXTREMELY DIFFICULT TO ESTIMATE THE
DAMAGES WHICH SELLER MAY SUFFER AS A RESULT THEREOF. THEREFORE BUYER AND SELLER
DO HEREBY AGREE THAT A REASONABLE ESTIMATE OF THE TOTAL NET DETRIMENT THAT
SELLER WOULD SUFFER IN THE EVENT THAT BUYER DEFAULTS AND FAILS TO COMPLETE THE
PURCHASE OF THE PROPERTY IN ACCORDANCE WITH THE TERMS OF THIS AGREEMENT AS A
RESULT THEREOF IS AND SHALL BE, AS SELLER'S SOLE AND EXCLUSIVE REMEDY, AN AMOUNT
EQUAL TO THE INITIAL CASH DEPOSIT OR TOTAL CASH DEPOSIT (IN ACCORDANCE WITH THE
TERMS OF THIS AGREEMENT ONLY) THEN IN THE POSSESSION OF THE TITLE COMPANY AND
ANY ACCRUED INTEREST THEREON. BUYER AND SELLER ACKNOWLEDGE AND AGREE THAT SAID
AMOUNT IS A REASONABLE SUM AND SHALL BE THE FULL, AGREED AND LIQUIDATED DAMAGES
FOR BREACH OF THIS AGREEMENT BY BUYER, ALL OTHER CLAIMS TO DAMAGES AND ANY OTHER
RELIEF, RIGHT OR REMEDY, AT LAW OR IN EQUITY, TO WHICH SELLER MIGHT OTHERWISE BE
ENTITLED BY REASON OF BUYER'S DEFAULT BEING HEREIN EXPRESSLY WAIVED BY SELLER.
IN THE EVENT THAT BUYER DEFAULTS AND FAILS TO COMPLETE THE PURCHASE OF THE
PROPERTY IN ACCORDANCE WITH THE TERMS OF THIS AGREEMENT, THIS AGREEMENT SHALL BE
TERMINATED AND NEITHER PARTY SHALL HAVE ANY FURTHER RIGHTS OR OBLIGATIONS
HEREUNDER, EACH TO THE OTHER EXCEPT FOR THE RIGHT OF SELLER TO RECEIVE SUCH
LIQUIDATED DAMAGES.

Initials:         Buyer  ________                    Seller  ________

                B.      Default by Seller. In the event the Closing does not
occur as herein provided by reason of any default by available at law or in
equity under California law, including the right (i) to terminate this Agreement
and to receive the prompt refund of the Initial Cash Deposit or Total Cash
Deposit (together with all accrued interest thereon), as applicable, plus
reimbursement by Seller of all costs, fees, and expenses incurred by Buyer in
connection with this transaction, including reasonable attorney's fees, or (ii)
to enforce specific performance of this Agreement or (iii) to pursue any other
remedy available to Buyer in law or in equity, including its claim for damages.

        17.     Work Product. Effective upon and in the event of a termination
of this agreement for any reason, Buyer shall assign and deliver to Seller, and
does hereby assign without the need for any further act or instrument, all
reports, plans, studies, documents, written information and the like which has
been generated by buyer in house or by Buyer's third party consultants, whether
prior to the opening of escrow or during the period of escrow in connection with
Buyers proposed acquisition, use, sale or development of the property
(collectively "Work Product"). In such event , Buyer shall deliver the Work
Product which has been assigned to seller not later than five (5) days after the
termination of this Agreement. The work product shall be fully paid for and
shall not be subject to any lien, encumbrance or claim of any kind.
<PAGE>
 
Buyer shall also return all information and materials given to it by Seller or
its consultants during escrow, in the same condition as delivered to Buyer.

        18.     Miscellaneous.

                A.      Attorney's Fees. In the event of the bringing of any
action or suit by a party hereto against another party hereunder by reason of
any breach or interpretation of this Agreement, then in that event the
prevailing party shall be entitled to recover from the other party all costs and
expenses of the action or suit, including reasonable attorneys' fees. In
addition, the prevailing party shall be entitled to recover all costs and
expenses including reasonable attorney's fees incurred by the prevailing party
in enforcing any judgment against the other party. The foregoing provision
relating to post-judgment costs is intended to be severable from all other
provisions of this Agreement.

                B.      Buyer's cooperation in a Section 1031 Tax Deferred
Exchange. Seller shall have the right to require the transfer of the Property be
effected by means of an IRS code Section 1031 tax deferred exchange and that the
Seller's rights and obligations under this Agreement may be assigned and/or
novated to another party for the purpose of completing such exchange without the
consent of Buyer. Buyer agrees to cooperate with the Seller and said other party
in a manner reasonably necessary to complete said exchange at no additional cost
or liability to Buyer, which cooperation shall include, without limitation,
executing such documents as made be reasonably necessary to effectuate such
exchange.

        Seller shall hold Buyer harmless from and indemnify and defend it
against any and all actions, causes of actions, claims, liens or other
proceedings, judgments, obligations, damages, losses or other liabilities, and
from all costs incurred in connection with the defense of any such claim or
claims, including reasonable attorney's fees and costs arising from, relating to
or connected with (i) any claim against Buyer arising out of or relating to its
participation in any exchange effectuated or attempted by Seller involving the
Property, and (ii) any other aspect of the accommodation by Buyer of any
exchange effected or attempted by Seller involving the Property. Seller's
indemnity obligation under this Section shall survive the Closing. In no event
shall (i) Buyer be required to take title to any other property in carrying out
this provision; or (ii) any such exchange extend the Scheduled Closing Date or
(iii) Buyer be required to assume any debt or execute any representation,
warranty, or indemnity for the benefit of a third party. Seller shall be
responsible for all costs and expenses reasonably incurred by Buyer in
implementing a tax deferred exchange benefiting Seller.

                C.      Costs. Unless otherwise specifically provided for
herein, Seller shall be responsible for all costs and expenses incurred by
Seller in effecting these transactions and Buyer shall be responsible for all
costs and expenses incurred by Buyer in effecting these transactions.

                D.      Entire Agreement. This Agreement contains the entire
agreement and understanding between the parties relating to the subject matter
hereof and may only be modified or amended by a written instrument executed by
the party against which enforcement of such amendment is sought. This Agreement
supersedes any prior agreements or negotiations of the parties. If any provision
or portion hereof shall be unenforceable, the remaining provisions or portions
of this Agreement shall be construed as if such provision or portion had not
been inserted herein. Each party has had independent legal advice on this
Agreement, or the opportunity to do so, and the meaning of the provisions
hereof; any interpretation shall be made in a neutral manner not for or against
either party based upon any attribution to such party as the source of the
language in question.

                E.      Time of Essence. Time is of the essence of each and
every term, condition, obligation and provision hereof and failure to comply
with this provision shall be a material breach of this Agreement.
<PAGE>
 
                F.      Counterparts. This Agreement may be executed in
counterparts, each of which shall be deemed an original, but all of which,
together, shall constitute one and the same agreement binding all parties
signatory to any counterpart.

                G.      Governing Law. This Agreement shall be governed by,
interpreted under, and construed and enforceable in accordance with, the laws of
the State of California. Venue shall be in Sacramento County.

                H.      No Third Party Benefit. This Agreement is intended to
benefit only the Buyer and Seller and no other person or entity shall acquire
any rights hereunder provided that this sentence shall not limit the right of
Buyer to assign its rights under this Agreement.

                I.      No Waiver. No failure to act or enforce a right
available to either party shall act as a waiver of that party's right and no
waiver of any right shall act as a waiver of any other right or of any future
application of the same right.

                J.      Severability: If any term or provision of this Agreement
is held unenforceable or invalid by a court of competent jurisdiction, the
remainder of the Agreement shall not be invalidated thereby but shall be
enforceable in accordance with its terms, omitting the invalid or unenforceable
term.

                K.      Successors And Assigns: The covenants and conditions of
this Agreement shall apply to and bind the heirs, successors, executors,
administrators and assigns of all the parties hereto; and all of the parties
hereto shall be jointly and severally liable hereunder. Notwithstanding anything
to the contrary in the Agreement, Buyer shall have the right to assign the
Agreement, or any of its rights, duties or obligations hereunder, to an entity
in connection with the implementation of any financing for the purchase of the
Property, including a sale/leaseback, any transaction commonly known as a
"synthetic lease", "tax ownership/operating lease", or "off balance sheet
financing", or any other arrangement with a related or unrelated entity pursuant
to which the assignee grants to Buyer (or any subsidiary or affiliate of Buyer)
the right to lease the Property following closing of the transaction
contemplated by this Agreement. In connection with any assignment by Buyer
permitted by this subparagraph, Buyer shall not be required to delegate any of
its duties under the Agreement, nor shall the assignee be required to assume any
of the obligations or liabilities of Buyer under the Agreement (including
liability for Buyer's representations and warranties under the Agreement), but
whether or not such duties are delegated or assumed, Buyer shall remain
personally liable for the performance of all of its obligations under this
Agreement following any such assignment. Additionally, Buyer, at no cost to
Seller, may cause Seller to transfer the Property at Close of Escrow to a
designee or nominee of Buyer.


IN WITNESS WHEREOF, Buyer and Seller have executed this Agreement and year first
above written.

Buyer:                                                Seller:
Objective Systems Integrators, Inc.    The John A. Sobrato 1979 Trust


By:  /s/ Philip N. Cardman                   By:  _____________________________
     ------------------------------
Date:  April 7, 1997                         Date:  ___________________________
     ------------------------------
Its:  VP and General Counsel                 Its:  ____________________________
     ------------------------------

The undersigned brokerage firms execute this Agreement solely for the purpose of
approving and accepting the provisions and limitations of Paragraph 15 hereof
entitled "Brokers."
<PAGE>
 
CB COMMERCIAL REAL ESTATE

By:  ____________________________________

COLLIERS ILEFF THORN

By:  ____________________________________




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