x86-64 on i386 (was Re: Promoting i386 version over x86_64?)

[Jon Masters]

On Tue, 2009-12-15 at 16:54 +0000, Paul Jakma wrote:
> On Mon, 14 Dec 2009, Chris Adams wrote:
> 
> > Have you actually shown any concrete benefits, or has it all just been
> > hand-waving?
> 
> Well, the benefits were already known from the introduction of 64bit 
> systems in the mid 90s. E.g. a rule of thumb with AXP systems was 
> that they required at least 30% odd more RAM, compared to other Unix 
> systems (either 32bit, or 32-userspace/64kernel systems - which is 
> what most of the other Unix RISC vendors went with when they went to 
> 64bit CPUs).

But again, Apples to Oranges. x86_64 (we should formally call it "Intel
64", or similar, since I'm not aware of x86_64 having a formal blessing)
doesn't have the fixed instruction width that you get on most RISC ISAs.

Not that any of it matters when we're already creeping up the minimum
memory requirements over time and not so interested in older hardware
anyway (e.g. recent i586/i686 changes). I know not everyone is living in
the US, but here at least someone drew my attention to a ludicrously
cheap laptop on sale last weekend that also had 3GB of RAM installed. I
think we should treat it like migrating to i686 and once everyone has a
64-bit capable (x86) CPU just plan to do a gradual migration over.

Jon.