Dual Core or Quad Core?

[Derek Atkins]

"Tom Buskey" <tom at buskey.name> writes:

> A few points:
>
> The Macintosh community had debates in the past about SMP vs single. 
> Generally they think a dual 500 MHz is roughly like a single 700MHz.  From
> that subjective information, I'd say more cores that are slightly slower are
> better.

This is probably true, as each core can be working on a separate
process so you have less context switching.

> I've felt that dual CPUs have lower latency when multitasking.  The OS runs on
> one CPU, software raid (why spend more for a dedicated hardware raid card?),
> your App on another, etc.  IMHO latency is more important then throughput for
> interactive use.

This is probably related to fewer context switches, but keep in mind
the memory bandwidth.

> I've been looking at a VMware ESX server.  it's licensed per 2 CPUs.  A 4 core
> is the same as a single or dual core in their licensing.  I'm finding with
> that, a dual quad core is cheaper then adding ram + 1 cpu to 2 systems with 3
> single core cpus between them.
>
> Those 1.6GHz CPUs might use less power & generate less heat.

"might" being the key operative word here.  Check the specs.

> The real limit on your application will likely be I/O.  Bus speed (FSB),
> network, disk speed, memory speed, etc.  How much data are they moving around?
>   More RAM will help more then CPU GHz also.

Keep in mind the memory bus issues.  In particular looking at Intel vs
AMD Quad-cores, the Intel quads are effectively two Dual-cores in a
single package and they share a memory controller, whereas the AMD
quads will theoretically each have a memory controller.  What this
means is that you get higher memory throughput (and lower latency) on
AMDs than Intels.  I just don't know which applications this effects.

-derek
-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
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