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                                                                     EXHIBIT 5.1


                   ALLEN, MATKINS, LECK, GAMBLE & MALLORY LLP
                      515 South Figueroa Street, Suite 700
                          Los Angeles, California 90071
                            Telephone: (213) 622-5555
                            Facsimile: (213) 620-8816


                                  July 15, 1998



Alpha Microsystems
2722 South Fairview Street
Santa Ana, California  92704

Ladies and Gentlemen:

         As counsel for Alpha Microsystems, a California corporation (the
"Company"), we are rendering this opinion in connection with the registration by
the Company on Registration Statement on Form S-3 (the "Registration Statement")
under the Securities Act of 1933, as amended, of up to 578,630 shares of the
Company's Common Stock, no par value (the "Shares"), to be offered for resale
for the account of selling stockholders of the Company. In acting as such
counsel, we have examined and relied upon the Registration Statement and the
originals, or copies certified or otherwise identified to our satisfaction, of
such corporate records of the Company and other documents and certificates of
fact as we have deemed necessary or advisable as a basis for the opinions
hereinafter expressed. In our examination, we have assumed the authenticity of
all documents submitted to us as originals, the genuineness of all signatures
thereon, the legal capacity of natural persons executing such documents and the
conformity to original documents of all documents submitted to us as copies. We
express no opinion with respect to any matters which may be, or purport to be,
governed by the laws of any state or other jurisdiction or country other than
the State of California and any federal law of the United States.

         Based upon the foregoing, and subject to the assumptions and
limitations set forth herein, we are of the opinion that the Shares have been
duly authorized, and upon exercise of the Warrants, the Shares will be validly
issued, fully paid and nonassessable. We hereby consent to the filing of this
opinion as an exhibit to the Registration Statement and to the use of our name
under the heading "Legal Matters" in the prospectuses forming a part of the
Registration Statement.

                                 Very truly yours,


                                 /s/ ALLEN, MATKINS, LECK GAMBLE & MALLORY LLP
                                 ---------------------------------------------
                                     Allen, Matkins, Leck Gamble & Mallory LLP