<PAGE>   1
                                                                    EXHIBIT 13.1


                 FIVE YEAR SUMMARY OF SELECTED CONSOLIDATED DATA


<TABLE>
<CAPTION>
                                                                           YEARS ENDED DECEMBER 31,
                                                   -----------------------------------------------------------------------
                                                     1998           1997          1996(1)          1995             1994
                                                   ---------      ---------      ---------       ---------       ---------
                                                                   (in thousands, except per share data)
<S>                                                <C>            <C>            <C>             <C>             <C>      
CONSOLIDATED STATEMENTS OF OPERATIONS DATA:

Revenues                                           $ 312,745      $ 267,858      $ 130,193       $  54,287       $  18,802
Cost of revenues                                     168,654        145,933         73,950          33,469          14,124
                                                   ---------      ---------      ---------       ---------       ---------
     Gross profit                                    144,091        121,925         56,243          20,818           4,678
                                                   ---------      ---------      ---------       ---------       ---------
Operating expenses:

     Research and development                         40,963         25,726         14,413           5,730           2,867
     Selling, general and administrative              65,328         42,653         21,188           9,660           5,051
     DSC litigation costs                                 --             --         18,947           1,623           4,551
                                                   ---------      ---------      ---------       ---------       ---------
          Total operating expenses                   106,291         68,379         54,548          17,013          12,469
                                                   ---------      ---------      ---------       ---------       ---------

Operating income (loss)                               37,800         53,546          1,695           3,805          (7,791)
Other income, net                                      4,055          4,866          2,388          (1,367)             26
                                                   ---------      ---------      ---------       ---------       ---------
Income (loss) before income taxes                     41,855         58,412          4,083           2,438          (7,765)
Income taxes (benefit)                                14,648         21,612         (3,154)             97              --
                                                   ---------      ---------      ---------       ---------       ---------

Net income (loss)                                  $  27,207      $  36,800      $   7,237       $   2,341       $  (7,765)
                                                   =========      =========      =========       =========       =========

Basic net income (loss) per share (2)              $    0.36      $    0.52      $    0.30       $    0.27       $   (1.27)
                                                   =========      =========      =========       =========       =========
Shares used in basic per share computations           74,788         70,131         24,146           8,746           6,093
                                                   =========      =========      =========       =========       =========
Diluted net income (loss) per share(2)             $    0.34      $    0.48      $    0.11       $    0.05       $   (1.27)
                                                   =========      =========      =========       =========       =========
Shares used in diluted per share computations         79,511         77,469         68,048          50,684           6,093
                                                   =========      =========      =========       =========       =========
</TABLE>

<TABLE>
<CAPTION>
                                                                            AS OF DECEMBER 31,
                                                      -----------------------------------------------------------------
                                                        1998          1997          1996          1995           1994
                                                      --------      --------      --------      --------       --------
                                                                                (in thousands)
<S>                                                   <C>           <C>           <C>           <C>            <C>     
CONSOLIDATED BALANCE SHEETS DATA:
Cash, cash equivalents and marketable securities      $110,753      $105,196      $108,430      $ 11,118       $  3,858
Working capital                                        209,324       193,640       145,338        18,770          6,809
Total assets                                           307,883       273,293       175,679        36,680         14,884
Redeemable convertible preferred stock                      --            --            --        37,777         23,546
Stockholders' equity (deficit)                         268,300       223,720       158,023       (15,765)       (15,706)
</TABLE>

(1)     Includes a charge of $15.8 million to reflect a cash payment of $10.1
        million and the issuance of 1,451,574 shares of Common Stock to DSC in
        settlement of outstanding litigation. Without this charge, operating
        income for the year ended December 31, 1996 would have been $17.5
        million.

(2)     See "Note 1 of Notes to Consolidated Financial Statements" for an
        explanation of the determination of the number of shares used in
        computing basic and diluted net income per share.