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                                                                   Exhibit 10.21
                                AMENDMENT NO. 1
                                       TO
                          AGREEMENT AND PLAN OF MERGER

                 THIS AMENDMENT NO. 1 TO AGREEMENT AND PLAN OF MERGER ("the
Amendment"), is entered into as of this 10th day of March, 1997, among Smith
Micro Software, Inc., a Delaware corporation ("Buyer"), PCI Video Products,
Inc., a Delaware corporation and a wholly owned subsidiary of Buyer ("the
Merger Subsidiary") and Performance Computing, Inc., an Oregon corporation
("the Company"), and shall serve to amend that certain Agreement and Plan of
Merger dated as of March 14, 1996, among the parties as follows:

                                    RECITALS

                 WHEREAS, the parties hereto entered into the Agreement and
Plan of Merger dated as of March 14, 1996 ("the Agreement") providing for the
Merger of the Company into the Merger Subsidiary on the Effective Time; and

                 WHEREAS, the parties desire to modify the terms of payments
due 365 days following the Closing as set forth in Sections 7.4 and 8.4 of the
Agreement;

                 INTENDING TO BE LEGALLY BOUND and in consideration of the
premises and mutual covenants and agreements contained herein and in the
Agreement, Buyer, Merger Subsidiary and the Company hereby agree as follows:

                                   AMENDMENT

                 The Agreement shall be amended to clarify the intentions and
agreements of the parties thereto in the manner and to the extent set forth
below.  All defined terms contained in this Agreement shall have the same
meaning as provided in the Agreement, unless otherwise specifically provided
herein.  All Section numbers set forth herein shall correspond to the Section
number of the Agreement being amended hereby.

         7.4     Milestones.  Section 7.4 of the Agreement shall be amended and
restated in its entirety as follows:

                 If all the targets set forth in Exhibit B hereto are achieved
                 during the 365 days following the Closing, then within ten
                 business days after March 14, 1997, Buyer shall pay to former
                 Company employees who are then current employees of Buyer or
                 the Merger Subsidiary Business (the "Current Employees")
                 $200,000 in the aggregate in cash.  Subject to the last
                 sentence of this Section 7.4, the payments pursuant to this
                 Section 7.4 will be paid to such





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                 Current Employees that are so designated by Buyer, after
                 consultation with the Sellers who are then employed by Buyer;
                 provided, that in all events, if all milestones are met, Buyer
                 shall pay out to such current Employees the entire $200,000.
                 If some, but less than all, of the targets set forth in
                 Exhibit B are achieved during the 365 days following the
                 Closing, then within ten business days after March 14, 1997,
                 Buyer shall pay to the Current Employees, in the same
                 percentages, form and manner set forth above, payments with an
                 aggregate value equal to the product of (i) $200,000 and (ii)
                 the aggregate of the percentages assigned to each of the
                 targets set forth on Exhibit B that are actually achieved
                 during such period.


         8.4     Earn Out.  Section 8.4 of the Agreement shall be amended and
restated in its entirety as follows:

                 If all of the targets set forth on Exhibit B hereto are
                 achieved during the 365 days following the Closing, then
                 within ten business days after March 14, 1997, Buyer shall pay
                 to Sellers Six Hundred Thousand Dollars ($600,000) in cash pro
                 rata based on each Seller's proportionate equity interest in
                 the Company immediately prior to the Closing.  If some, but
                 less than all of the targets set forth on Exhibit B are
                 achieved during the 365 days following the Closing, then
                 within ten business days after March 14, 1997, Buyer shall pay
                 to Sellers in the same percentages and manner set forth above,
                 the product of (i) Six Hundred Thousand Dollars ($600,000)
                 and (ii) the aggregate of the percentages assigned to each of
                 the targets set forth on Exhibit B that are actually achieved
                 during such period.


                 Except as specifically provided hereinabove, all other
provisions of the Agreement shall remain in full force and effect and are
hereby ratified and confirmed by the parties.





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                 IN WITNESS WHEREOF, the parties hereto have caused this
Amendment to be duly executed by their respective authorized officers as of the
day and year first above written.

                               Buyer:  Smith Micro Software, Inc.


                               By:  /s/ William W. Smith, Jr.  
                                    --------------------------------------------
                                    William W. Smith, Jr.  
                                    Title: President and Chief Executive Officer



                               Merger Subsidiary:  PCI Video Products, Inc.


                               By:  /s/ William W. Smith, Jr.  
                                    --------------------------------------------
                                    William M. Smith, Jr.  
                                    Title: President and Chief Executive Officer



                               The Company:  Performance Computing Inc.


                               By:  /s/ Daniel C. Budge 
                                    --------------------------------------------
                                    Daniel C. Budge 
                                    Title:  President



                               Sellers (executing solely for purposes of those 
                               provisions applicable to them):


                               /s/ Daniel C. Budge 
                               -------------------------------------------------
                               Daniel C. Budge


                               /s/ David N. Glass 
                               -------------------------------------------------
                               David N. Glass


                               /s/ Carol E.G. Vallens 
                               -------------------------------------------------
                               Carol E.G. Vallens





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