Intel C2D COREs not used equally in FreeBSD 7.0-CURRENT i386

Dag-Erling Smørgrav des at
Wed Jun 6 10:47:58 UTC 2007

Oliver Fromme <olli at> writes:
> It's a common mistake to assume that amd64 only makes sense
> if you have >= 4GB RAM.  There are several reasons why it
> might be useful to switch from i386 to amd64:
>  - Most programs (though not all) will run faster, because
>    in amd64 mode there are twice as many general-purpose
>    registers, giving compilers much better opportunities
>    for optimizations and caching of values, and reducing
>    slow memory accesses.

"twice as many" is an understatement.  AMD64 has 16 GPRs vs i386's 8 if
you consider BP, SI, DI and SP as GPRs (as the AMD and Intel literature
does); in practical terms the score is 12 to 4.

>  - Some applications might benefit from a larger virtual
>    address space > 4 GB.  (Note that this is not related
>    to the amount of physical RAM!)

For instance, Varnish maps its entire storage into memory, and will
benefit greatly from the increased address space.

> In practice there's (almost) only one reason not to run
> FreeBSD/amd64 on amd64-capable hardware:  If you depend
> on a certain piece of software which is known not to run
> correctly in 64bit mode.  Fortunately those are not many.

The only one I can think of (for a desktop) is the Flash plugin.

Dag-Erling Smørgrav - des at

More information about the freebsd-current mailing list