[GLLUG] Lightweight

[Richard Houser]

> Why? All Pentium D's are dual core 64 bits.

You need to understand what's really happening at a microcode layer, as the
chips are essentially RISC cores.  It's basicall a 32 bit chip core that
they bolted AMD's x86_64 instruction set and some extra hardware support
onto.  From what I recall, the core of the chip was not designed to run
64-bit, and doesn't perform as well in that mode as something like an X2
that was orignally designed to do so.  For something like an X2, basic
operations in 64 bit mode are just as fast as the 32 bit equivalents, but
from what I was hearing on the Pentium-4 cores the D is based, that was far
from the case.

Even then, a balanced 64 bit chip like an X2 is sometimes faster on 32-bit
mode depending on the task.  64-bit modes give you access to hardware
virtualization, crypto features, more reigsters, 64-bit address spaces, and
64-bit alu operations, but those longer addresses do take more memory
bandwidth to communicate.  Depending on really low level details like
algorithm critical loops vs cache size, etc. even some modern stuff can run
better in 64-bit modes depending on the task at hand.  For example, a
virtual server guest (like under xen, kvm, vmware etc.) is generally
recommended to be 32-bit if you have less than 2-4gb of memory.  If you
will only be running 32-bit apps, you will also save time not having to
swap back and forth between 32 and 64 bit operating modes each time the OS
goes back to the kernel.

On Sun, Aug 2, 2015 at 2:14 PM, Philip Robar <philip.robar at gmail.com> wrote:

> On Sun, Aug 2, 2015 at 1:33 PM, Richard Houser <rick at divinesymphony.net>
> wrote:
>
>> Make sure to use an i586/i686 distro rather than x86_64 for that chip.
>> For a similar era AMD X2 or such, stick with x86_64.
>>
>
> Why? All Pentium D's are dual core 64 bits.
>
> Phil
>
>
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