PROSPECTUS SUPPLEMENT                         FILED PURSUANT TO RULE 424(b)(3)
(To Prospectus dated July 10, 1997)           Registration No. 333-30199


                            DATA GENERAL CORPORATION

                 $212,750,000 Principal Amount of 6% Convertible
                           Subordinated Notes due 2004
                    (Interest payable May 15 and November 15)

                        8,122,089 Shares of Common Stock



        This document supplements the Prospectus dated July 10, 1997 relating to
(i) $212,750,000 aggregate principal amount of 6% Convertible Subordinated Notes
due 2004 (the "Notes") of Data General Corporation,  a Delaware corporation (the
"Company"), and (ii) 8,122,089 shares of common stock, par value $.01 per share,
(the "Common Stock") of the Company which are initially issuable upon conversion
of the Notes plus such additional indeterminate number of shares of Common Stock
as may become  issuable upon  conversion of the Notes as a result of adjustments
to the  conversion  price  (the  "Shares").  The Notes and the  Shares are being
offered  for the  account  of the  holders  thereof.  The Notes  were  initially
acquired from the Company by Morgan Stanley & Co.  Incorporated and Dillon, Read
& Co., Inc in May 1997 in connection  with a private  offering.  This Prospectus
Supplement is incorporated by reference into the Prospectus,  and all terms used
herein shall have the meaning  assigned to them in the  Prospectus.  On July 30,
1997 the last sale  price of the  Common  Stock of the  Company  on the New York
Stock  Exchange was $30 3/8ths.  The Common Stock of the Company is traded under
the symbol "DGN."

         Selling Securityholder: The Northwestern Mutual Life Insurance Company
                                 720 East Wisconsin Avenue
                                 Milwaukee, WI  53202



         Securities Being Sold:  $3,250,000.00 (1)  aggregate principal amount
                                                    of 6% Convertible
                                                    Subordinated Notes due 2004


(1) Includes  $250,000.00 in principal  amount held in The  Northwestern  Mutual
Life Insurance Company Group Annuity Separate Account.The Selling Securityholder
has shared voting and shared investment power with respect to
this $250,000.00 amount.


         As of July 30,  1997,  and  prior to  giving  effect to the sale of the
Notes  being  offered  by  the  Selling   Securityholder   hereby,  the  Selling
Securityholder  beneficially owned  $3,250,000.00  aggregate principal amount of
Notes,  [representing 1.5% of the Notes outstanding as of such date]. As of July
30, 1997, the following two affiliates of the Selling Securityholder own the 
Company's Common Stock, as follows:

     Northwestern Mutal Series Fund, Inc.  8,200 shares (Balanced Portfolio)

                                           5,400 shares (Index 500 Portfolio)

     Mason Street Funds, Inc.                200 shares (Index 500)




SEE "RISK  FACTORS"  BEGINNING ON PAGE 4 OF THE  ACCOMPANYING  PROSPECTUS  FOR A
DESCRIPTION  OF  CERTAIN  FACTORS  THAT  SHOULD  BE  CONSIDERED  BY  PROSPECTIVE
INVESTORS.




            THESE SECURITIES HAVE NOT BEEN APPROVED OR DISAPPROVED BY
               THE SECURITIES AND EXCHANGE COMMISSION OF ANY STATE
            SECURITIES COMMISSION NOR HAS THE SECURITIES AND EXCHANGE
            COMMISSION OR ANY STATE SECURITIES COMMISSION PASSED UPON
                THE ACCURACY OR ADEQUACY OF THIS PROSPECTUS. ANY
                         REPRESENTATION TO THE CONTRARY
                             IS A CRIMINAL OFFENSE.



                    The date of this Prospectus Supplement is
                                 July 31, 1997.