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Re: comments about hardware

On Mon, Jul 18, 2005 at 01:36:55AM -0400, Faheem Mitha wrote:
> 1) Dual core Opterons first came on the market in April. The sales rep 
> said that AMD Dual Core Opterons did not work with Fedora Core. Since they 
> only install Fedora and SuSE, they had no info about Debian. Any idea what 
> the status is here? How well are they supported, and how stably do they 
> run under Linux?
> Also, I was told that a dual core Opteron, which is somewhat more than 
> twice the cost two regular Opterons of similar speed, is not equivalent to 
> two regular Opterons in functionality. Can anyone point me to information 
> about this, or offer a comment?

One dual core opteron compared to two single core opterons:

Each opteron has a memory controller built in that does dual channel
memory support.  A dual core opteron still only has one memory
controller and hypertransport to the chipset.  The two cores share it,
so two single cores have theoretically twice the memory bandwidth of a
single dual core.  Of course they also require a dual socket board
rather than a single socket board, and you could put two dual core
opterons in a dual board and get to use 4 cores total without having to
pay for a much more expensive 4 socket board.  Two cores in one package
may on the other hand have faster access to each other's caches which
may be an advantage in some situations, while in others sharing the
memory bandwidth could hurt.  At the same time the dual core would
always have it's memory local, while two single cores half the ram is
likely connected to the other cpu so access would have a 1 cycle penalty
for access.  A decent OS would try to make sure applications are running
on the cpu whos ram they are currently in whenever possible.

Len Sorensen

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