Re: New IA64 binaries run on Old IA64 computers ?

From: L. Blunt (withheld_at_my.choice)
Date: 06/05/04 

Date: Sat, 5 Jun 2004 08:16:52 +0100

> There is also /ARCHITECTURE=xxx, which uses the
> instruction set present on the specified architecture.
> If you compile /ARCH=EV6 and then run on an EV4 CPU,
> it will use EV6 instructions that don't exist on EV4,
> and so will trap. However, VMS V7.1 and later provide
> an instruction emulator for the missing instructions,
> so it will emulate the EV6 instruction and continue,
> at a fairly substantial performance penalty.
>

I thought is worth mentioning that this is not entirely new idea for
Alpha's. The later VAX chips were missing some instructions that the
original VAX 780 (eg: MOVC3, MOVC5, the BCD ones), but when run on a version
of VMS that supported the newer MicroVAX they were trapped and emulated them
in libraries.

The only difference is adding instructions, as opposed to removing them.

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