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From: sutter@osu-eddie.UUCP (Bob Sutterfield)
Newsgroups: fa.info-vax
Subject: Re: The value of a VAX 750
Message-ID: <620@osu-eddie.UUCP>
Date: Mon, 23-Sep-85 09:42:42 EDT
Article-I.D.: osu-eddi.620
Posted: Mon Sep 23 09:42:42 1985
Date-Received: Tue, 24-Sep-85 03:34:01 EDT
References: <8509201641.AA17976@UCB-VAX.ARPA>
Organization: OSU Instruction & Research Computer Center
Lines: 40

> ...
> 1) Is this true? (That is, is the 750 essentially an obsolete
> paperweight nowadays?)
> 
> 2) If true, can it be fixed? Are the defects in the 750 so basic that it
> cannot be brought up to current standards of good performance by
> replacing or upgrading certain parts? If it can be, is it known if DEC
> has researched this and is planning to (or already does) provide a path
> for making the 750 perform as well as the average new machine of
> comparable size?
> ...
> Regards, 
> Will Martin
> 
> ARPA/MILNET: wmartin@almsa-1.ARPA    UUCP/Usenet: seismo!brl-bmd!wmartin

There have always been rumors that the developers of the 750 were
constrained by marketing considerations to slow down the CPU by inserting
no-ops in the microcode.  This was to keep it from being too close to the
compute speed of the 780, which was a good first stab at implementing the
architecture, but slower than an implementation using more current
technology (witness the 785 upgrade).  I once asked a DEC Field Service rep
who claimed (and seemed) to know a good bit about the microcode situation,
and he "unofficially" confirmed the story.

If this is the case, a 750 could be pumped up to a "755" with nothing more
than a new rev release of the console TU58, containing de-no-opped (is that
a word?) microcode.  This wouldn't, of course, make up for the paucity of
buffered data paths and a slower UNIBUS (as compared to the 780), but it
would certainly help.
-- 
    Human: Bob Sutterfield
           Facilities Management Division
           The Ohio State University Instruction & Research Computer Center
Workplace: Ohio Cooperative Extension Service, Computer Management Group
           OCES VAX System Manager/Programmer (VMS)
     Mail: ...cbosgd!osu-eddie!sutter.UUCP
       or: sutter@ohio-state.CSNET
       or: 2120 Fyffe Rd rm 109, Columbus OH  43210
   MaBell: (614) 422 - 9034