<TABLE> <S> <C>

<PAGE>

<ARTICLE> 5
<LEGEND>
THIS SCHEDULE CONTAINS SUMMARY FINANCIAL INFORMATION EXTRACTED FROM XIRCOM,
INC.'S FORMS 10-Q FOR THE QUARTERLY PERIODS ENDED MARCH 31, 1997 AND MARCH 31,
1998, AND THE FORM 10-K FOR THE FISCAL YEAR ENDED SEPTEMBER 30, 1996, AND IS
QUALIFIED IN ITS ENTIRETY BY REFERENCE TO SUCH FINANCIAL STATEMENTS. (RESTATED)
</LEGEND>
<MULTIPLIER> 1,000
       
<S>                             <C>                     <C>                     <C>
<PERIOD-TYPE>                   6-MOS                   12-MOS                   6-MOS
<FISCAL-YEAR-END>                          SEP-30-1997             SEP-30-1996             SEP-30-1998
<PERIOD-START>                             OCT-01-1996              OCT-1-1995             OCT-01-1997
<PERIOD-END>                               MAR-31-1997             SEP-30-1996             MAR-31-1998
<CASH>                                          65,537                  21,377                  72,069
<SECURITIES>                                         0                       0                       0
<RECEIVABLES>                                   52,278                  28,440                  33,587
<ALLOWANCES>                                     2,870                   3,434                   5,919
<INVENTORY>                                     16,680                  13,771                  23,210
<CURRENT-ASSETS>                               139,677                  71,545                 133,909
<PP&E>                                          34,918                  34,467                  43,371
<DEPRECIATION>                                  16,888                  16,331                  18,819
<TOTAL-ASSETS>                                 173,654                 107,201                 159,070
<CURRENT-LIABILITIES>                           37,245                  36,834                  38,628
<BONDS>                                              0                       0                       0
<PREFERRED-MANDATORY>                                0                       0                       0
<PREFERRED>                                          0                       0                       0
<COMMON>                                            23                      20                      23
<OTHER-SE>                                     131,643                  65,583                 119,940
<TOTAL-LIABILITY-AND-EQUITY>                   173,654                 107,201                 159,070
<SALES>                                        113,449                 166,757                 116,679
<TOTAL-REVENUES>                               113,449                 166,757                 116,679
<CGS>                                           70,893                 107,437                  76,922
<TOTAL-COSTS>                                   70,893                 107,437                  76,922
<OTHER-EXPENSES>                                29,751                  50,308                  33,629
<LOSS-PROVISION>                                     0                       0                       0
<INTEREST-EXPENSE>                                   0                       0                       0
<INCOME-PRETAX>                                 12,891                   7,674                   8,151
<INCOME-TAX>                                     3,867                   2,506                   2,444
<INCOME-CONTINUING>                              9,024                   5,168                   5,707
<DISCONTINUED>                                   (226)                     784                       0
<EXTRAORDINARY>                                      0                       0                       0
<CHANGES>                                            0                       0                       0
<NET-INCOME>                                     8,798                   5,952                   5,707
<EPS-PRIMARY>                                      .43                     .31                     .25
<EPS-DILUTED>                                      .41                     .30                     .25
        

</TABLE>