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                                  EXHIBIT 3.21

                  CERTIFICATE OF DETERMINATION OF PREFERENCES
                                       OF
                            SERIES T PREFERRED STOCK
                                       OF
                                   DISC, INC.


      We, J. Richard Ellis and Henry Madrid, hereby certify that we are the
President and the Chief Financial Officer, respectively, of DISC, INC., a
corporation organized and existing under the General Corporation Law of the
State of California, and further, DO HEREBY CERTIFY:

      That pursuant to the authority conferred upon the Board of Directors by
the Articles of Incorporation of the said Corporation, the said Board of
Directors on March 31, 1999 adopted the following resolution creating a series
of 16,089 shares of Preferred Stock designated as Series T Preferred Stock, none
of which shares have been issued:

            "RESOLVED, that pursuant to the authority vested in the Board of
      Directors of the corporation by the Articles of Incorporation, the Board
      of Directors does hereby provide for the issuance of a series of Preferred
      Stock, no par value, of the Corporation, to be designated "Series T
      Preferred Stock," initially consisting of 16,089 shares and to the extent
      that the designations, powers, preferences and relative and other special
      rights and the qualifications, limitations and restrictions of the Series
      T Preferred Stock are not stated and expressed in the Articles of
      Incorporation, does hereby fix and herein state and express such
      designations, powers, preferences and relative and other special rights
      and the qualifications, limitations and restrictions thereof, as follows
      (all terms used herein which are defined in the Articles of Incorporation
      shall be deemed to have the meanings provided therein):


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            Section 1. Designation and Amount. The shares of such series shall
      be designated as "Series T Preferred Stock," no par value, and the number
      of shares constituting such series shall be 16,089.

            Section 2. Dividends and Distributions.

                    (A) Subject to the prior and superior right of the holders
      of any shares of Series C Preferred Stock ranking prior and superior to
      the shares of Series T Preferred Stock with respect to dividends, and pari
      passu with the rights of the holders of shares of Series D Preferred
      Stock, Series E Preferred Stock, Series F Preferred Stock, Series G
      Preferred Stock, Series H Preferred Stock, Series I Preferred Stock,
      Series J Preferred Stock, Series K Preferred Stock, Series L Preferred
      Stock, Series M Preferred Stock, Series N Preferred Stock, Series O
      Preferred Stock, Series P Preferred Stock, Series Q Preferred Stock,
      Series R Preferred Stock and Series S Preferred Stock with respect to
      dividends, subject to the rights of any series of Preferred Stock which
      may hereafter come into existence, the holders of shares of Series T
      Preferred Stock shall be entitled to receive when, as and if declared by
      the Board of Directors out of funds legally available for the purpose,
      dividends in the same amount per share as declared on the Common Stock,
      treating such number of shares of Series T Preferred Stock for this
      purpose as equal to the number of shares of Common Stock into which it is
      then convertible. In the event any dividends are declared or paid on the
      outstanding shares of any series of Preferred Stock with dividend rights
      ranking pari passu with the Series T Preferred Stock, dividends shall
      simultaneously be declared and paid on the outstanding shares of Series T
      Preferred Stock, pari passu with the shares of such other series of
      Preferred Stock with dividend rights ranking pari passu with the Series T
      Preferred Stock, based upon the number of shares of Common Stock into
      which shares of Series T Preferred Stock and such other series of
      Preferred Stock with dividend rights ranking pari passu with the Series T
      Preferred Stock are then convertible. In the event the Corporation shall
      at any time after the date of the filing of this Certificate of
      Determination of Preferences (the "Rights Declaration Date") (i) declare
      any dividend on Common Stock payable in shares of Common Stock, (ii)
      subdivide the outstanding Common Stock, or (iii) combine the outstanding
      Common Stock into a smaller number of shares, then in each such case, the
      amount of Common Stock or other consideration to which holders of shares
      of Series T Preferred Stock were entitled immediately prior to such event
      under the preceding sentences of this Section 2(A) shall be adjusted as
      set forth in Section 4(C) hereof.

                    (B) The Corporation shall declare a dividend or distribution
      on the Series T Preferred Stock as provided in paragraph (A) above prior
      to declaring a dividend payable on shares of Common Stock.

            Section 3. Voting Rights. The holders of shares of Series T
      Preferred Stock shall have the following voting rights:

                    (A) Each holder of Series T Preferred Stock is entitled to a
      number of votes equal to the number of shares of Common Stock into which
      the holder's Series T Preferred Stock is then convertible. In the event
      the Corporation shall at any time after the Rights Declaration Date (i)
      declare any dividend on Common Stock payable in shares of Common Stock,
      (ii) subdivide the outstanding Common Stock, or (iii) combine the
      outstanding Common Stock into a smaller number of shares, then in each
      such case the number of votes per share to which holders of shares of
      Series T Preferred Stock were entitled immediately prior to such event
      shall be adjusted as set forth in Section 4(C) hereof.

                    (B) Except as otherwise provided herein or by law, the
      holders of shares of Series T Preferred Stock and the holders of shares of
      Common Stock (and any authorized series of Preferred Stock convertible
      into shares of Common Stock and with voting rights equal to the number of
      shares of Common Stock into which such series of Preferred Stock is then
      convertible) shall vote together as one class on all matters submitted to
      a vote of shareholders of the Corporation.

                    (C) Except as required by law or under Section 8 hereof,
      holders of Series T Preferred Stock shall have no special voting rights
      and their consent shall not be required (except to the extent they are
      entitled to vote with holders of Common Stock as set forth herein) for
      taking any corporate action.


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            Section 4. Conversion Rights.

                    (A) Each holder of Series T Preferred Stock may, at any
      time, in such holder's sole discretion, convert all or any part of such
      holder's shares of Series T Preferred Stock into fully paid and
      nonassessable shares of Common Stock at the rate of ten (10) shares of
      Common Stock for each share of Series T Preferred Stock surrendered for
      conversion.

                    (B) Such conversion may be effected by surrender of such
      holder's certificate or certificates for the shares of Series T Preferred
      Stock to be converted, duly endorsed, at the principal office of the
      Corporation, with a written notice stating (i) that such holder elects to
      convert all or a specified number of shares of Series T Preferred Stock
      into shares of Common Stock, and (ii) the name in which such holder
      desires a certificate for the shares of Common Stock to be issued.
      Promptly thereafter, the Company shall issue and deliver to such holder a
      certificate for the number of shares of Common Stock to which such holder
      shall be entitled. Such conversion shall be deemed to have been made at
      the close of business on the date of such surrender, and such holder shall
      be treated for all purposes as the record holder of such shares of Common
      Stock on that date.

                    (C) In the event the Corporation shall at any time after the
      Rights Declaration Date (i) declare any dividend on Common Stock payable
      in shares of Common Stock, (ii) subdivide the outstanding Common Stock, or
      (iii) combine the outstanding Common Stock into a smaller number of
      shares, then, in each case, the number of shares of Common Stock issuable
      upon the conversion of each share of Series T Preferred Stock shall be
      adjusted by multiplying such amount by a fraction, the numerator of which
      is the number of shares of Common Stock outstanding immediately after such
      event and the denominator of which is the number of shares of Common Stock
      that are outstanding immediately prior to such event.

                    (D) In the event the Corporation shall at any time or from
      time to time after the Rights Declaration Date make or issue, or fix a
      record date for the determination of holders of Common Stock entitled to
      receive, a dividend or other distribution payable in securities of the
      Corporation or any of its subsidiaries, or of any other corporation or
      third party, other than in shares of Common Stock, then, in each such
      event, provisions shall be made so that the holders of Series T Preferred
      Stock shall receive, upon the conversion thereof, securities of the
      Corporation or any of its subsidiaries or of any other corporation or
      third party which they would have received had their stock been converted
      into Common Stock on the date of such event.

              Section 5. Reacquired Shares. Any shares of Series T Preferred
      Stock purchased or otherwise acquired by the Corporation in any manner
      whatsoever shall be retired and canceled promptly after the acquisition
      thereof. All such shares shall upon their cancellation become authorized
      but unissued shares of Preferred Stock and may be reissued as part of a
      new series of Preferred Stock to be created by resolution or resolutions
      of the Board of Directors, subject to the conditions and restrictions on
      issuance set forth herein.

            Section 6. Liquidation, Dissolution or Winding Up.

                    (A) Upon any liquidation (voluntary or otherwise),
      dissolution or winding up of the Corporation, following the first priority
      liquidation preference of the Series C Preferred Stock in the amount of
      $5.00 per share plus any declared but unpaid dividends, and pari passu
      with the liquidation preference of the Series D Preferred Stock in the
      amount of $5.00 per share plus any declared but unpaid dividends ("Series
      D Liquidation Preference"), the liquidation preference of the Series E
      Preferred Stock in the amount of $4.00 per share plus any declared but
      unpaid dividends ("Series E Liquidation Preference"), the liquidation
      preference of the Series F Preferred Stock in the amount of $8.00 per
      share plus any declared but unpaid dividends ("Series F Liquidation
      Preference"), the liquidation preference of the Series G Preferred Stock
      in the amount of $20.00 per share plus any declared but unpaid dividends
      ("Series G Liquidation Preference"), the liquidation preference of the
      Series H Preferred Stock in the amount of $38.30 per share plus any
      declared but unpaid dividends ("Series H Liquidation Preference"), the
      liquidation preference of the Series I Preferred Stock in the amount of
      $4.19 per share plus any declared but unpaid dividends ("Series I
      Liquidation Preference"), the liquidation preference of the Series J
      Preferred


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      Stock in the amount of $2.98 per share plus any declared but unpaid
      dividends ("Series J Liquidation Preference"), the liquidation preference
      of the Series K Preferred Stock in the amount of $3.19 per share plus any
      declared but unpaid dividends ("Series K Liquidation Preference"), the
      liquidation preference of the Series L Preferred Stock in the amount of
      $2.76 per share plus any declared but unpaid dividends ("Series L
      Liquidation Preference"), the liquidation preference of the Series M
      Preferred Stock in the amount of $2.23 per share plus any declared but
      unpaid dividends ("Series M Liquidation Preference"), the liquidation
      preference of the Series N Preferred Stock in the amount of $0.90 per
      share plus any declared but unpaid dividends ("Series N Liquidation
      Preference"), the liquidation preference of the Series O Preferred Stock
      in the amount of $1.06 per share of Series O Preferred Stock plus any
      declared but unpaid dividends (the "Series O Liquidation Preference"), the
      liquidation preference of the Series P Preferred Stock in the amount of
      $8.20 per share of Series P Preferred Stock plus any declared but unpaid
      dividends (the "Series P Liquidation Preference"), the liquidation
      preference of the Series Q Preferred Stock in the amount of $6.20 per
      share of Series Q Preferred Stock plus any declared but unpaid dividends
      (the "Series Q Liquidation Preference"), the liquidation preference of the
      Series R Preferred Stock in the amount of $5.80 per share of Series R
      Preferred Stock plus any declared but unpaid dividends (the "Series R
      Liquidation Preference"), and the liquidation preference of Series S
      Preferred Stock in the amount of $3.20 per share of Series S Preferred
      Stock plus any declared but unpaid dividends (the "Series S Liquidation
      Preference"), no distribution shall be made to the holders of shares of
      stock ranking junior (either as to dividends or upon liquidation,
      dissolution or winding up) to the Series T Preferred Stock unless, prior
      thereto, the holders of shares of Series T Preferred Stock shall have
      received an amount equal to $20.20 per share of Series T Preferred Stock
      plus any declared but unpaid dividends ("Series T Liquidation
      Preference").

                    (B) In the event, however, that there are not sufficient
      assets available to permit payment in full of the Series D Liquidation
      Preference, the Series E Liquidation Preference, the Series F Liquidation
      Preference, the Series G Liquidation Preference, the Series H Liquidation
      Preference, the Series I Liquidation Preference, the Series J Liquidation
      Preference, the Series K Liquidation Preference, the Series L Liquidation
      Preference, the Series M Liquidation Preference, the Series N Liquidation
      Preference, the Series O Liquidation Preference, the Series P Liquidation
      Preference, the Series Q Liquidation Preference, the Series R Liquidation
      Preference, the Series S Liquidation Preference, the Series T Liquidation
      Preference and the liquidation preferences of all other series of
      Preferred Stock, if any, which rank on a parity with the Series T
      Preferred Stock, then such remaining assets shall be distributed ratably
      to the holders of such parity shares in proportion to their respective
      liquidation preferences.

            Section 7. No Redemption. The shares of Series T Preferred Stock
      shall not be redeemable.

            Section 8. Amendment. The Articles of Incorporation of the
      Corporation shall not be further amended in any manner which would (a)
      alter or change the powers, preferences or special rights or privileges of
      the Series T Preferred Stock so as to affect them adversely or (b) grant
      to any other class of shares any rights superior to those of the Series T
      Preferred Stock without the affirmative vote of the holders of a majority
      or more of the outstanding shares of Series T Preferred Stock, voting
      separately as a class.

            Section 9. Fractional Shares. Series T Preferred Stock may be issued
      in fractions of a share which shall entitle the holder, in proportion to
      such holder's fractional shares, to exercise voting rights, to receive
      dividends, to participate in distributions and to have the benefit of all
      other rights of holders of Series T Preferred Stock."


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      The undersigned declare under penalty of perjury that the matters set
forth in the foregoing Certificate are true of their own knowledge.

      Executed at Milpitas, California on October 21, 1999.

                                                  /S/    J. Richard Ellis
                                           -------------------------------------
                                                       J. Richard Ellis
                                           President and Chief Executive Officer


                                                  /S/    Henry Madrid
                                           -------------------------------------
                                                       Henry Madrid
                                                 Chief Financial Officer