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March 26, 2006 by Chris Thomson
(cmthomson at comcast dot net)
Chris has been a computer system architect at Myrias Research, Amdahl, 3Com, Nokia and others for the last 20+ years. An ex-pat
Canadian, he now resides in sunny Pleasanton, CA. Chris used to think that people who build their own PCs and then overclock them
are nuts. Now he's certain of it.
What Chris describes in the following article is the construction of a system based around an Intel Pentium D 830 dual core processor, overclocking the CPU, and finally, making it run as quietly as possible despite the extreme >130W heat. The great attention to detail makes this one of the best documented DIY articles we've posted. Thank you, Chris!
- Mike Chin, Editor of SPCR
THE ORIGINAL IDEA
I do a lot of transcoding of audio and video on my home
computer, and got tired of the system being unusably slow for hours at
a stretch during transcoding or other activities such as virus scans.
This was not a particularly slow system (a 2.53 GHz, 1 GB-RAM Pentium 4 HP 754n),
but it sure ground to a halt when busy. I knew
that the solution to this would be a dual-core CPU. When the Intel
Pentium D came out, a guy at work convinced me it would be
"tons of fun" to build a system around one of these chips.
I can safely say that I've met the original goal, but it's
been quite an adventure. Along the way, I discovered the joys of
designing, assembling, overclocking, cooling, quieting and
measuring such a system. As my first-ever do-it-yourself PC, it was a remarkable learning
experience. I started the research in August 2005, and quit tinkering
in November. Then of course as I was finishing this article, I made more changes.
SELECTING A CPU
All I knew at the start of this was that I wanted a dual-core CPU, and had a preference for a Pentium (it's a long story). Intel had just
introduced a four-member family, the 820 D, 830 D, 840 D and 840 Extreme Edition. All of these are bin selections and bond-outs of the
Smithfield chip, which is basically two Prescotts on a single die, each with a 1MB L2 cache. All variants support 64-bit mode.
I immediately ruled out the 840 EE as a useless marketing gimmick. Four threads instead of two would provide no practical speedup, and the $1000 price tag was just silly.
Scanning the Pentium D reviews on Newegg,
I encountered some scathing comments about the 820 being a different
architecture from the others, and not being well-supported by graphics
processors. Sure enough, perusing Intel's data
sheet revealed the existence of the PRB (platform requirement bit), which is zero for
the 820 and one for the others. The main difference the PRB makes is in power consumption. The 820 has a TDP (thermal design power) of 95W, whereas the others have a TDP of 130W.
That's a huge difference, and implies that setting PRB=0 cripples some pretty important performance features. Accordingly, I
chose the 830 D, largely because it is a lot cheaper than the 840D, which has the same chip inside.
NB: If you're building a system now (in early 2006), you should choose a member of the 65-nm Pentium D 900 Presler family, which has
caches twice as large as the 90-nm Smithfield, and uses less power. You might also consider using a Yonah or Sossaman instead; these are 32-bit-only CPUs
and much more expensive, but they have similar performance while consuming a third as much power.
SELECTING A HEATSINK
Virtually every review of the Pentium D pointed out that it is One Hot Mama.
Most of the reviews complain about the stock Intel cooler being noisy and not particularly effective. I came across many
references to the Scythe Ninja cooler, and a quick Google took me to its SPCR
review. I was hooked: this was the heatsink for me. Unfortunately it was out of stock, so I did the initial system build with the Intel cooler. No
doubt about it, that fan is loud. Also, the temperature was quite high, even with Arctic Silver
5 in place of the obviously compromised stock thermal tape.
Ninja heatsink w/120mm fan, from the SPCR review.
I ordered a 120mm DustProof
AcoustiFan to attach to the Ninja, since I was dubious about dissipating >130W passively, even with the two case fans close by. This turned out to be
a very valid concern. When the Ninja arrived I swapped coolers and was much happier.
SELECTING A MOTHERBOARD
Since this system would be used for general computing and not gaming,
I had no interest in SLI
(the last game I spent much time playing was Adventure;
gosh I'm old!). However, I did want dual-channel memory, which is the PC-world name for interleaving. I also wanted an abundant set of SATA and IDE connectors, DDR2 memory, and PCI-Express support.
P5LD2 met my requirements. All of its components are passively cooled, except of course for the
CPU. Although it wasn't a consideration at the time, it also has the advantage of using a 4-pin 12V connector. More on this later. This motherboard has
all the overclocking features you'd want: independent FSB, memory and PCI clocks, independently adjustable core, MCH [Editor's Note: Memory Controller Hub, more commonly referred to as the Northbridge chip] and DRAM voltages, etc.
There are lots of other fine motherboards out there, but this one has worked well for me. The only issues I encountered were excessive motherboard heat buildup and Vcore droop under full load. More on this later.
SELECTING THE MEMORY
As mentioned above, I wanted to use DDR2 memory. With two cores running independent programs, the higher the
memory bandwidth, the better. Also, my old 1GB system swapped more than
I like, so I wanted 2 GB.
DDR2 memories run at very high clock rates, but typically have
Higher latency translates directly into lower system performance, since
the CPU is unable to do anything useful while it's waiting on the
memory. The main consideration in choosing the memory DIMMs for my
system was a tradeoff between CAS latency and price. Since I
overclock by boosting the FSB frequency, I also wanted memory that
would run faster than the standard 533 MHz.
There are lots of DDR2 DIMMs that are rated at PC2 5300 (667
PC2 5400 (675 MHz). Most have latencies of 5. For a little more money,
you get a latency of 4. For a lot
more money, you get a latency of 3.
In the end, I chose 2 GB of Corsair
These are matched pairs of 512MB DIMMs, rated at 675 MHz with 4-4-4-12
timing at 1.8V. At the time, they cost a little over $200 for the set.
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