[LAU] OT: 32-bit vs 64-bit speeds

[Lee Revell]

On Feb 4, 2008 2:36 AM, Erik de Castro Lopo <mle+la at mega-nerd.com> wrote:
> david wrote:
>
> > Just curious, but I've heard that 64-bit OSes are slower than 32-bit
> > ones. That seems odd to me. Any truth to it?
>
> Swings and roundabouts.
>
> On architectures like Sparc where the 32 and 64 bit CPUs have the same
> number of registers, the 64 bit OS is likely to be a little slower
> on operatrions like traversing linked lists because each pointer is
> twice as big on 64 bit and hence each retrieval of a pointer requires
> twice as much memory bandwidth as the 32 bit OS.
>

Right.  I presumed that he was comparing a 32 to a 64 bit OS on the
same (64 bit) hardware, in which case I would not expect a difference;
it's just as fast to load a 32 bit pointer as a 64 bit one.  Unless
the compiler is smart enough to fetch two 32 bit words at once
whenever possible ;-)

Lee