Are Two CPUs Better
Than One?
The test : Two CPUs are better than one,
right? That’s what most people believe.
To test this hypothesis, we used one
big mofo of a mobo: Tyan’s Thunder
K8W, stuffed with a pair of AMD 2.2GHz
Opteron 248 CPUs. Unlike the Xeon
CPU, which uses a shared system bus
for memory access, the Opteron’s
nonuniform memory architecture
(NUMA) has a separate point-to-point
connector for each CPU’s memory
access, which theoretically results in
faster performance. (Unfortunately,
the architecture of the Thunder K8W
isn’t recognized by the 32-bit version
of Windows XP, so we won’t see any
increased performance from NUMA
until Microsoft gets the 64-bit version
of its OS.)
To keep the two CPUs happy, we
outfitted each with a pair of 512MB
registered DDR400 RAM modules.By running separate modules, the
AMD 8000-series chipset is able to
run in 128-bit mode interleaved for
improved memory access. We loaded
a fresh install of Windows XP Pro with
SP1 onto a 250GB Western Digital
WD2500JB drive and paired it with
an ATI Radeon 9800 Pro card and the
Catalyst 4.3 drivers. We tested both the
dual- and single-CPU setups with
a wide variety of software.The results : Lab tests prove that two
CPUs can indeed be better than one.
The key word here is can. Not every
application takes advantage of multiple
processors, and some that do don’t
add a whole lot of performance. Take
Wolfram Research’s Mathematica 5
as an example. One CPU, two CPUs,
or four CPUs makes no difference
to this number-crunching app—that
second proc might as well be a college
buddy crashing on your couch. Sadly,
Mathematica’s zero percent increase
with dual CPUs is representative of whatyou’ll get with most of the apps and
games on the market today. While the
benchmark chart on the opposite page
indicates faster performance across the
board for the two-proc rig, if you look
closely, you’ll see that, more often than
not, the difference is minimal.
Quake III Arena is the sole odd duck
of the bunch. This golden oldie of a 3D
shooter actually offers some limited
(but quirky) two-processor support. It’s
not a fully supported feature, but we
did witness a small performance bump,
which is more than most games will
give you. On the downside, however,
the frame rates for QIIIA were far below
what we get on our single-processor
zero-point system.
Adobe spent a lot of time and
money to retool Premiere into Premiere
Pro , and the result is much improved
multi-threading support. But in our
tests, the second processor netted just
an 11 percent increase in speed. That’s
not bad, but it’s also not great when
you factor in the cost of running a two-Is that the Death Star or a mobo? We used
Tyan’s mighty Thunder K8W to test whether
two CPUs are better than one.MAXIMUMPC JUNE 2004
SPEED
EXPERIMENTS WITH