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

[Dan Cross]

In article <ucbh82$8kpo$2 at dont-email.me>,
Arne Vajhøj  <arne at vajhoej.dk> wrote:
>[snip]
>DEC chose to have the VAX switch mode between 32 and
>16 bit instructions (similar to what AMD did a couple
>of decades later).

One presumes you are referring to amd64 here.  If so, then nope,
amd64 is an extension to 32-bit x86, not a replacement in the
sense that the VAX ISA replaced the PDP-11 ISA when the mode bit
was set.

Even in 64-bit mode, many (most?) programs will continue to
operate as expected with 32- and even many 16- bit instructions.
The same was not true of the VAX.

>DG chose to support both instruction sets at the
>same time.

Perhaps you should read, "Soul of a New Machine."

	- Dan C.