[Info-vax] VAX vs. MV/8000 [was Re: Hard links on VMS ODS5 disks]

[Rich Alderson]

=?UTF-8?Q?Arne_Vajh=c3=b8j?= <arne at vajhoej.dk> writes:

 [ snip ]

> There is an obvious case: Data General was in a relative similar situation to
> DEC.

> DEC had a PDP-11 mini-computer with various 16 bit OS (RSX, RSTS/E, RT-11,
> IAS etc.) and they came up with the VAX and the 32 bit VMS.

> Data General had an Eclipse mini-computer with 16 bit AOS and they came up
> with the Eclipse MV with the 32 bit AOS/VS.

The Eclipse was an extension of the 16 bit Nova family, with additional
instructions done by changing the meaning of certain NOPs.

> Same business problem. Same point in time.

> So I tried to compare design.

> (disclaimer: for Eclipse MV and AOS/VS entirely based on various internet
> source - I have no experience with them myself)

> VAX + VMS                               Eclipse MV + AOS/VS
> ---------                               -------------------

> CISC                                    CISC
> 32 bit virtual byte addresses           31 bit virtual word addresses
> 4 GB address space                      4 GB address space
> 512 byte pages                          2 KB pages
> 16 bit compatibility mode               16 bit compatibility mode

Wrong!  See below.

> 4 modes:                                8 modes:
>    K (0) - VMS                             0 - kernel
>    E (1) - RMS & Rdb                       1 - virtual adress translation
>    S (2) - DCL                             2 - unused
>    U (3) - application                     3 - IO buffering & compatibility
>                                            4 - DG database
>                                            5 - Oracle database
>                                            6 - available for large  applications
>                                            7 - applications
> memory organized:                      memory organized in 512 MB segments one per mode
>    P0 - heap
>    P1 - stack
>    S0 - OS
>    S1 - unused (early VMS)
> processes                               processes + threads (called tasks)
> kernel in Macro-32 or Bliss             kernel in assembler
> utilities in Macro-32 or Bliss or HLL   utilities in Algol dialect

> Not similar enough to suspect industrial espionage but similar enough to
> support my claim that DEC choices back then made sense given what was known.

Unlike the PDP-11 mode bit in the VAX, the MV/8000 used the same method as the
Eclipse to add 32 bit intructions to the mix:  A previously unused set of NOPs
was turned into the prefixes for the 32 bit instruction set.

I refer you to a nontechnical description of the development of the MV/8000,
Tracy Kidder's _The Soul of a New Machine_, and to the historical pages
available from Wild Hare (wildhare.org), Bruce Ray's company which now holds
the rights to all of the Data General software.

Disclaimer:  I have no dog in this fight.  Bruce is a good friend, but I've never
worked on DG systems.

-- 
Rich Alderson					  news at alderson.users.panix.com
      Audendum est, et veritas investiganda; quam etiamsi non assequamur,
	  omnino tamen proprius, quam nunc sumus, ad eam perveniemus.
									--Galen