Although the Extreme Edition series got off to a wobbly
start in the NetBurst Pentium days – it was much more expensive than
standard CPUs, but not much faster – the brand took a turn for the
better when Intel started using the Core architecture. The first such
chip was the Core 2 Extreme
X6800, which was soon followed by the first quad-core CPU, the QX6700,
and then by a slighter higher clocked model in the form of the QX6800.
It should come as no surprise, therefore, that as well as the new
1,333MHz Core 2 Duos, there’s also a new Extreme model: the Core 2
Extreme QX6850. Sensibly, this quad-core CPU still comprises two
separate dual-core dies packaged together.
This makes manufacturing quad-core CPUs much easier and more
flexible than the single-die approach of AMD; Intel can simply
cherry-pick dies from dual-core production lines, making quad-core
parts as demand dictates. With this simple and sensible approach to
quad-core production, Intel is
already selling its tenth quad-core CPU, while AMD has yet to make its
first.
One
downside is that Intel has to match the two dual-core dies, since the
LGA775 socket only provides one voltage plane. Even so, here’s some
leeway, since cores 0 and 1 ran 3-5 degrees C hotter than cores 2 and 3
in our test CPU. Another downside is that the 8MB of Level 2 cache is
split across the two dies, with each pair of cores sharing 4MB. Each
core retains 32KB of Level 1 cache.
The QX6850 has the same hefty 130W TDP as that of the QX6700 and
QX6800, so it requires effective cooling. However, like all Core 2
Extremes, the QX6850 is very hardy; it’s happy up to 100 degrees C,
while a standard Core 2 Duo will throttle its speed at 85 degrees C.
Not only is the QX6850 armed with a
faster FSB than the QX6800, which had an FSB of 266MHz (1,066MHz
effective), but it also runs faster at 3GHz, rather than 2.93GHz. This
may only be a 67MHz increase but, combined with the higher FSB (which
provides the QX6850 with more
memory bandwidth than the QX6800), the QX6850 should be faster.Like all
Extreme CPUs, the QX6850 has an unlocked multiplier, so it’s easy to
overclock.
To find out how much of a difference these higher frequencies make,
we tested the QX6800 and QX6850 in the same test rig. This was the same
PC that we used for the CPUs on the opposite page, so you can directly
compare all the results on these two pages. While the dual-core
1,333MHz CPUs were no faster than their 1,066MHz counterparts, this
chip proved
to be faster than its predecessor, and by more than the extra the clock
speed merits. The QX6850 was a good 6 per cent faster than the QX6800
in the memory bandwidth intensive multitasking test (making it 0.14
faster in our scoring
system). Comparing only frequencies, this QX6850 is just 2 per cent
faster than the QX6800; clearly, the increased FSB does a better job of
feeding the four cores.
Following this discovery, we eschewed the usual approach of
overclocking a Core 2 Extreme by increasing its bus multiplier in
favour of increasing the FSB, thereby obtaining maximum performance.
Our test chip had a VID of 1.3375V, but by
increasing its vcore to 1.525V, we were able to boost the FSB from
333MHz (1,333MHz effective) to 418MHz (1,672MHz effective). With its
bus multiplier set at nine, this overclocked the QX6850 from 3GHz to
3.76GHz, further than the
QX6800, which we could only overclock to 3.6GHz.
At 3.76GHz, the QX6850 proved to be faster than an Olympic
athlete on steroids and is the first air-cooled CPU to score 3.00 in
our Media Benchmarks. This is an incredible achievement, given that
other CPUs need to be
phase-change-cooled to handle an overclock capable of achieving such a
high score.
CONCLUSIONLike all Extreme Edition CPUs, the Core 2 Extreme QX6850 is
considerably more expensive than a standard CPU. Just compare the
prices of the processors opposite, and you’ll appreciate the premium
that Intel charges for this chip. However, there’s no denying the
QX6850’s awesome performance. The 1,333MHz FSB makes it a good deal
faster than previous quad-core CPUs, and it overclocks further too. A
Core 2 Extreme may not be for everyone but, if you have the cash and
want the very best, then nothing comes close to the awesome power of
the Core 2 Extreme QX6850.
Author: James Gorbold
Intel Core 2 Extreme QX6850