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                                                                     EXHIBIT 5.1

                        WILSON SONSINI GOODRICH & ROSATI
                               650 PAGE MILL ROAD
                               PALO ALTO, CA 94304
                                 (650) 493-9300

                                  May 17, 2001

Sun Microsystems, Inc.
901 San Antonio Road
Palo Alto, CA  94303

         RE: REGISTRATION STATEMENT ON FORM S-8

Ladies and Gentlemen:

         We have acted as counsel to Sun Microsystems, Inc., a Delaware
corporation (the "Company") and have examined the Registration Statement on Form
S-8 (the "Registration Statement") to be filed by the Company with the
Securities and Exchange Commission on or about May 17, 2001 in connection with
the registration under the Securities Act of 1933, as amended (the "1933 Act")
of 2,146,655 shares of the Company's Common Stock, par value $0.00067 per share
(the "Shares"), reserved for issuance under the HighGround Systems, Inc. Stock
Option Plan, as amended (as amended, the "Plan").

         As your legal counsel, we have examined the Restated Certificate of
Incorporation, as amended, and Bylaws of the Company, the Plan and such other
documents of the Company as we have deemed necessary or appropriate for the
purposes of the opinion expressed herein, and are familiar with the proceedings
proposed to be taken by the Company in connection with the operation and
administration of the Plan and the sale and issuance of the Shares pursuant to
the Plan.

         It is our opinion that the Shares, when issued and sold in the manner
referred to in the Plan and pursuant to the agreements which accompany the Plan,
will be legally and validly issued, fully paid and nonassessable.

         We consent to the use of this opinion as an Exhibit to the Registration
Statement and further consent to the use of our name wherever appearing in the
Registration Statement and any subsequent amendment thereto.

                                   Sincerely,

                                   WILSON SONSINI GOODRICH & ROSATI
                                   Professional Corporation

                                   /s/ WILSON SONSINI GOODRICH & ROSATI