js wrote:
> I just asked for a quote from a Sun supplier ... it turns out that
> asking for a one dual-core AMD Model 720 CPU is more expensive than
> going for a 2x single-core AMD Model 248 CPU.
>
> Is the price difference worth it ?

First of all, the 270 runs at 2.0GHz and the 248 runs at 2.2GHz, so a dual
248 has slightly more raw processor grunt than a single 270.

The choice of being worth it or not depends what you're looking for really.
If you're sure that you're going to only need 2 processors, then a dual 248
is almost certainly a better deal. You get more memory bandwidth (each
processor has dual-channel PC3200, compared to the 270 only having single
dual-channel PC3200), more raw computing power, more HT links, basically
more of everything on the performance side{*}. The dual-core Opterons'
strong points are mainly higher core density. You get more cores per watt
and more cores for the same space. Additionally, the cost of a dual
dual-core system is lower than that of a 4-CPU single-core system.

So, if you were pretty sure you're only going to need two cores, a dual 248
system makes more sense. If, on the other hand, you have a decent chance of
doing an upgrade to four cores in the near future, it'd be a better move to
get a single 270 system so that you can drop in a second CPU later when you
need it. It's a somewhat risky thing to do due to the higher upfront cost,
and only really worth it if you're planning to do the upgrade within a year
or so.

[...]

{*} The dual-core CPU does enjoy slightly lower cache-to-cache transfer
times (the transactions go directly through the
higher-bandwidth-lower-latency crossbar, as opposed to the hypertransport
bus) but there are few applications that benefit much from this. The halving
of the memory bandwidth on the dual-core system is far more likely to have
an impact on performance in most cases.

--
Michael Brown
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