[Info-vax] Some questions on software for VMS 7.3 VAX

[Stephen Hoffman]

On 2016-01-01 06:30:32 +0000, David Froble said:

> With exceptions, you can use VAX/VMS V7.3 for most of what you can do 
> on Alpha, itanic, and hopefully soon x86-64.
> 
> Then there are some things that are available only on VAX, and not on 
> the newer platforms.
> 
> One of the really good things about VMS is that it's more "timeless" 
> than many other environments.  Also, you've been a bit extreme with 
> "80s HW paltform". VAXs were being sold well into the late 1990s, I 
> believe.


That.... depends.   BASIC didn't diverge much from VAX days, beyond the 
interpreter no longer being available.   But which also means that 
BASIC didn't advance very much.

As for the hardware, VAX is a comparative fossil, very limited in 
memory and capabilities, and increasingly difficult to back-port 
OpenVMS software onto.   Other than BASIC, and other code that didn't 
adopt newer APIs and 64-bit.

VAX ran into architectural walls in the 1980s particularly around 
memory addressing and the size of system space, and — particularly 
starting after V6.1, which was the so called "functional equivalence" 
release — OpenVMS on Alpha and Itanium has diverged substantially from 
what VAX offered.

OpenVMS VAX V6.0 and later are also intentionally compatible at the 
user and the kernel interfaces, meaning that — as compatibility 
inherently forces — comparatively little changed.

Code written for newer platforms can be a pain in the rump to 
back-port, due to the lack of 64-bit and the lack of various newer APIs 
and itemcodes.




BTW: among with a few other architectural details, it was the ubiquity 
of the condition codes that helped end any thoughts of overhauling VAX 
to a newer design.   Everything was a potential test instruction, which 
then made pipelining and multi-issue a much larger effort.

Condition codes: 
http://h30266.www3.hp.com/odl/vax/opsys/vmsos73/vmsos73/4515/4515pro_014.html#9_processorstatuslongwordpsl 


VAX XPA & XVA: http://labs.hoffmanlabs.com/node/131

-- 
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