[Info-vax] Hard links on VMS ODS5 disks

[Arne Vajhøj]

On 7/24/2023 8:50 PM, Arne Vajhøj wrote:
> On 7/24/2023 1:12 PM, Simon Clubley wrote:
>> We are talking about structural and design issues within VMS that is
>> making this porting process a lot more involved than it should be.
> 
> There are two very different questions:
> 
> #1: Did DEC's decisions in 1977 make sense given 1977 knowledge?
> 
> #2: Did DEC's decisions in 1977 make sense given 2023 knowledge?
> 
> I believe the answer to #1 is YES. Their decisions was similar to how
> most OS was designed at the time.
> 
> The answer to #2 is probably NO, because they should have gone
> with a HLL, they should have prepared for future migrations to other
> ISA, they should have prepared for 64 bit, they should have
> focused more on security etc.etc..
> 
> But trying to evaluate decisions of the past using todays
> knowledge is a totally futile exercise.
> 
> If you plan on inventing a time machine and travel back in
> time to tell them to do things differently, then maybe. But
> otherwise then accept that decisions was made based on
> available information at the time for the decisions. And
> complaining about such decisions does not change a thing.
> 
> There is a term for it "Monday morning quarterback".

Since the "DEC did it wrong" line is coming up
again I did an attempt to verify my claim about
#1 above.

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.

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
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.

Arne