64-bit CPU

[Lennart Sorensen]

On Wed, Sep 15, 2004 at 10:26:05PM -0400, Christopher Browne wrote:
> I see little point to jumping to 64 bit mode on the AMD64 laptops.
> 
> - They don't support more than about 1GB of RAM, which means you're not
>   getting any improvement over 32 bit mode
> 
> - Widening addresses to 64 bits and likely widening some instructions,
>   is likely to decrease performance somewhat.
> 
> This doesn't point to there being any lowlying fruit to the jump to 64
> bits...

Well so far the Debian amd64 port has noticed upwards of 50% performance
increase in many applications (I don't know which though).  That would
indicate a reason to go 64bit.

I remember seeing one benchmark that showed the athlon64 could do 64bit
calculations in 64bit mode as fast as 32bit math in 32bit mode, and
32bit math in 64bit mode about twice the speed of in 32bit mode.

So it does make a difference, not just for ram size allowed.

You could even memory map a huge file (over 4GB) in 64bit mode if that
makes your application easier to implement. :)

Lennart Sorensen
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