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                                                                     EXHIBIT 5.1


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

                               December 19, 2000


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" or "You") 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 December 19, 2000 in
connection with the registration under the Securities Act of 1933, as amended,
shares of the Company's Common Stock, par value $0.00067 per share (the
"Shares"), reserved for issuance under the Cobalt Networks, Inc. Amended and
Restated 1997 Employee Stock Plan, Cobalt Networks, Inc. 1999 Director Option
Plan, 1999 Stock Option Plan of Chili!Soft, Inc., 1998 Stock Option Plan of
Chili!Soft, Inc., and 1997 Stock Option Plan of Chili!Soft, Inc. (the "Plans").

        As your legal counsel, we have examined the proceedings taken and are
familiar with the proceedings to be taken in connection with the sale and
issuance of said Shares under the Plans. It is our opinion that the Shares, when
issued and sold in the manner referred to in the Plans and pursuant to the
agreements which accompany the Plans, the Shares 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 amendment thereto.

                                       Very truly yours,

                                       WILSON SONSINI GOODRICH & ROSATI
                                       Professional Corporation


                                       /s/ WILSON SONSINI GOODRICH & ROSATI