<PAGE>
PROSPECTUS SUPPLEMENT DATED JUNE 17, 1998
TO PROSPECTUS DATED MAY 8, 1998
$150,000,000
[LOGO]
6% CONVERTIBLE SUBORDINATED NOTES DUE 2005
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THIS PROSPECTUS SUPPLEMENT SHOULD BE READ IN CONJUNCTION WITH THE PROSPECTUS
DATED MAY 8, 1998 (THE "PROSPECTUS"). THE SELLING HOLDERS TABLE ON PAGE 66 OF
THE PROSPECTUS IS HEREBY SUPPLEMENTED TO INCLUDE ADDITIONAL SELLING HOLDERS AS
INDICATED IN THE FOLLOWING TABLE:
<TABLE>
<CAPTION>
NUMBER OF SHARES OF
AGGREGATE COMMON STOCK
PRINCIPAL AMOUNT ISSUABLE UPON
OF NOTES OWNED AND CONVERSION OF NOTES
NAME OF SELLING HOLDER THAT MAY BE SOLD THAT MAY BE SOLD(1)
- - ---------------------------------------------------------------------- ------------------ ---------------------
<S> <C> <C>
BancAmerica Robertson Stephens........................................ $ 2,400,000(2) 84,656
Deeprock & Co......................................................... 500,000(3) 17,636
Glacier Water Services, Inc........................................... 900,000(3) 31,746
NationsBanc Montgomery Securities..................................... 22,150,000(4) 781,305
The Class IC Company, Ltd............................................. 500,000(5) 17,636
</TABLE>
- - ------------------------
(1) Includes only full shares of Common Stock issuable upon conversion of the
Notes based on an initial conversion price of $28.35 per share (initially
equivalent to a conversion price of 35,273 shares per $1,000 principal
amount of Notes). A cash payment will be made in lieu of any fractional
interest upon conversion.
(2) The holdings of this entity are as of June 8, 1998.
(3) The holdings of this entity are as of June 2, 1998.
(4) The holdings of this entity are as of June 15, 1998. NationsBanc Montgomery
Securities has engaged in transactions with and performed various investment
banking and other services for the Company in the past and may do so from
time to time in the future.
(5) The holdings of this entity are as of June 9, 1998.
