Pentium 805D has an interesting surprise

Jarod Wilson jarod at wilsonet.com
Wed Apr 25 15:04:43 EDT 2007


On Wednesday 25 April 2007 13:56:35 Ben Scott wrote:
> On 4/25/07, Thomas Charron <twaffle at gmail.com> wrote:
> > Yes, this is exactly why I say the differences from a software
> > perspective are debatable.
>
>   In the sense of what you have to program to make use of it, yes.
> Either way, you have to worry about shared memory concurrency,
> locking, re-entrance, all that stuff.  But the performance
> characteristics are quite different.
>
>   Dual core and quad core is just SMP (symmetric multi-processor)
> implemented in a single IC package.  It used to be this was done at
> the motherboard level -- two sockets, two IC packages, and special SMP
> chipsets.  Dual core just fits everything into a single IC package,
> and makes the SMP chipset standard.  A single dual-core processor is
> "exactly" the same thing as a conventional dual processor system.
>
>   (I put "exactly" in quotes because there are some differences.  For
> example, I understand some cache sharing is possible on some chips.
> But it's really really really close to classic x86 SMP.)

There's another big difference in the AMD64 world that should be noted. Since 
the memory controller is on-chip, a multi-socket opteron system winds up 
being NUMA-capable (multiple independent memory controllers and banks of 
dimms directly accessible by a specific socket), whereas a 
single-socket/multi-core opteron/athlon64 isn't NUMA-capable, all cores share 
direct access to the same memory.

-- 
Jarod Wilson
jarod at wilsonet.com


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