Silencing a P4-1.6A oc'd to 2GHz

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April 13, 2002 - by Mike Chin

It is a computing axiom that you can't have fast and quiet; certainly not without resorting to elaborate and exotic cooling systems these days. This is due mostly to the hot multi-gigahertz CPUs from both AMD and Intel, which have likely caused a average increase in PC noise output of at least 2 dB/year since 1999, as discussed in this article about noise emission trends in electronic equipment. Recently, after reading about the higher efficiency of Intel's 0.13-micron Northwood core P4s, I decided to put the axiom to the test: Can a P4 be made to run silently at 2-Ghz using non-exotic, inexpensive techniques? Attempting to answer this question was a great excuse to succumb the siren call of speed glorious speed - once again.

The Strategy

In every PC project, one has a strategy, whether improvised or carefully planned out. My approach this time was mixed. I needed the P4, a motherboard for it, and DDR memory. But I had enough other components lying around that could be used. I also wanted to prove at least to myself that making a quiet computer does not necessarily mean spending a lot of money on specialty products.

I hoped to use an existing case, modified for excellent airflow so that case fans would not be necessary, with a decent PSU powerful enough for the current demands of the P4 but not too expensive. Hopefully, the retail P4 heatsink and fan would be quiet enough to be used. If necessary, I would replace the PSU and heatsink fans with quieter ones or run them at low voltage.

The P4 and other New Goodies

A retail Intel P4-1.6A was purchased, along with a MSI 645 Ultra 333 (SiS chipset) motherboard and a 256 MB stick of generic PC2100 DDRAM. The P4-1.6A is a 0.13 micron core CPU with 512K of cache introduced just a few months ago. It has been touted as the new Celeron 300A for its extreme overclockability.

First, a picture of the siren herself. The part number is SL668. It was packed on 01/31/02 and made in Costa Rica. The most surprising aspect of the CPU is its size. The photo doesn't show the scale, but it is TINY, measuring just a bit over 1" square. Intel calls the metal piece that covers over 90% of the top surface a heat spreader. The large contact area helps the heat from core to be dissipated out to the heatsink more efficiently. It also protects the die from damage during heatsink installation - a problem too often seen with the AMD socket-A CPUs. The other surprise is the modest price: In late February 2002, at a local Vancouver shop, it cost just Cdn $235 plus taxes, which worked out to around US$165 in total.

What Watts?

Initially, I was led to believe that the power dissipation of this P4 at its rated 1.6 GHz clock speed and 1.5V core voltage is 38.7 watts. That's the number touted all over the web: more than 20 watts lower than the equivalent clock P4 of the previous 0.18 micron Willamette variety, and 10W lower than the power rating of the AMD T-bird 1GHz in one of my systems.

Later, I learned I was misinformed.

There are 2 versions of the P4-1.6A. According to Intel's documentation about the P4, my 1.6A SL668 is a normal 46.8W 1.6A. At time of writing, all retail box P4-1.6A are the 46.8W variety.

The low wattage 38.0W P4-1.6A is part # SL62S, designated as an OEM part. However, OEM versions of the Northwood core P4 cannot be found anywhere locally in Vancouver or on the Internet. Local retailers said the price difference between the two versions is so small they felt there was no point ordering the OEM, especially considering minimum ordering requirements.

This meant I was dealing with 9 watts more than expected. Pretty much the same wattage as my 1 GHz T-bird. Grrrr! Still, I had managed to silence the T-bird, so?

NOTE: Added June 14, 2002

According to one source, the actual power dissipation of the two P4 versions discussed above is the same; they are the same processor. The lower power version simply can't handle as much peak power before burning up. Average power dissipation and thermal efficiency is the same.

The Retail P4-1.6A Package

The retail Intel heatsink-fan (HSF) that came with the CPU is more impressive than expected.

The heatsink is fairly large at 2.75"D x 3.25"W x 1.375"H, with 25 fins on a contoured base that is thicker in the center. The all-aluminum heatsink weighs ~300 grams, and the fan & mounting clip add ~75 grams. A thermal pad was attached to the base. I removed it with the help of an old credit card, then baking soda, dish soap and a sponge with water. With fan detached, of course. The bottom surface is not mirror-polished like many expensive heatsinks but smooth enough that I didn't feel there was any need for lapping.

The fan design is much like that on previous Intel processors where the housing is a single-piece mold that clips tightly to the HS. Compared to photos of stock HSF on other P4s I have seen (see the 2nd photo on right), this fan looks smaller. I believe the fan & the heatsink have been changed for the 0.13 micron Northwood.

The standard core voltage of the NW P4 is 1.5V, compared to 1.75V of the older 0.18-micron core Willamette P4s; power dissipation has dropped by approximately 25% for processors of the same speed. For example, the nominal power spec for the 'Willamette' core 1.6G P4 is 61W while that for the P4 1.6A is 46.8W.

So perhaps because of the reduced cooling requirement Intel reduced the fan size, and perhaps the heatsink? If so, it is unfortunate for HSF silencing, as smaller diameter fans always whine more while delivering less airflow, and smaller heatsinks require more airflow for the same level of cooling.

Examining the fan closely, it appears that something of the augmented fan technology of the Millennium Glaciator and the PBL Panaflo fans may be in use here. There is little or no frame to speak of, as both in / out flow sides are almost completely open.

Considering its small 60mm blade size and 3000-rpm speed, it's not that noisy. It's rated at 0.16A, made by Sanyo-Denki, and has a part number (109X9412T5H036) that looks like one of Sanyo-Denki's. I could not find this part on their website nor Intel's, so can only guesstimate that the CFM is in the mid-20s, and its dBA spec around 30. It is whinier & noisier than my reference quiet fan, the 80mm Panaflo FBA08A12L, rated at just 21 dBA.

The HSF mounting clip is a clever affair that uses two cam action levers to clamp the heatsink tightly to the motherboard, sandwiching the CPU in between. The levers are in a plastic frame that comprises half of the mounting clip. The other half is a plastic frame that is already on the motherboard, around the CPU socket. It is a bit fiddly with the MSI motherboard because of capacitors mounted close to one side of the plastic frame. But all in all, HSF mounting is relatively simple and stress-free, unlike many of the clipped HSF for socket CPUs, especially with the added security of the protective metal heat-spreader cover over the core.

An animated GIF shows how this works -- not a great sequence, but gives you the general idea. (If the pic below is not animated, hit the browser refresh or reload button -- the GIF is set to repeat 10 times, then stop so it doesn't drive you batty.)

Bowing to Pressure

Still this setup is not without problems. So much pressure is applied that the motherboard actually gets bowed directly beneath the CPU socket. That's right: the motherboard gets bent. It worried me when I noticed it, so I did some web research to see if there was any reference to it.

The Australian Dan of Dan's Data said in a review of P4 heatsinks:

Intel have tried to convince people that bending the bejaysus out of their motherboard is a good thing, because if something smacks the computer then the CPU socket's less likely to pop off the board... I remain unpersuaded... These coolers don't actually break anything, at least in the short term. They just look as if they ought to.

At Intel, digging through the P4 support area, I came across this document, which says:

...the thermal solution provides controlled compression on the processor and socket. This compression results in curvature in the motherboard... It is normal to observe a bow or bend in the motherboard. The level of bow or bend depends on the motherboard material properties and component layout.

An accompanying PDF document showed this photo, presumably to reassure (!?) the alarmed builder:

What can be said? The pressure applied to the motherboard seems excessive. Intel even cautions about making sure the distance between the back of the mobo and the case is adequate to accommodate this bowing. Modifying the mounting bracket to reduce the pressure would probably help motherboard longevity if you plan to play around with fans, heatsinks, etc.

I did come up with a solution to reduce the bowing; more on that later.

Intel P4 HSF Shuffle

One month after the purchase of the above retail P4 package, I purchased a second one, ostensibly the same package as the first. In early March, Intel caused some excitement among hardware nuts when they released photos of a new heatsink they said would soon be shipped with P4. The photo showed an AVC Sunflower HSF, which had already been reviewed as an excellent performance HSF. So I had hopes that my 2nd P4 might be so equipped.

Alas, no such luck. What I got instead was a plain-Jane rectangular block HSF that

  • Weighed 250 grams, or about 50 less than the previous one
  • Had a slightly larger, less whiney but noisier fan; in fact, the older fan shown in the photos above.

What gives? I don't know. Intel's attitude seems to be: They'll take what we give 'em. They don't have a choice.



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