COOLING SOCKET 478 PRESCOTTS

Practical tips – Bryan Bain and Dave Casole

The Prescott is the third generation of Intel Pentium 4 processors. Released after some delays during the first quarter of 2004, the Prescott P-4 is based on a 90 nm core compared to the 130 nm core of the Northwood or the 180 nm core of the Willamette.

To achieve this latest core shrink, Intel implemented a new “strained silicon” technology. This article is not going into much detail of the Prescott architecture, but basically Intel is using smaller gate lengths, longer execution pipelines and about twice as many transistors as compared to the Northwood. Some other significant differences worth noting: the L1 cache was increased from 8k to 16k, the L2 cache jumped from 512k to 1024k, and default vcore voltage was reduced.

The Prescott P-4 is available in 533 MHz system bus speed with no Hyperthreading and 800 bus with Hyperthreading. Recently, the Prescott Celeron D was released for the budget minded. The Prescott is also produced in two socket flavors, the 478 pin CPU and the newer pinless LGA775 CPU. We will focus on the P-4 socket 478 versions and leave the rest for future articles.

OK, enough of all that technical mumbo jumbo. How does the Prescott live up to the initial hype and high expectation?

Well to be very blunt, the early Prescotts certainly had heat issues and were not received kindly by the critics. Apparently the strained silicon leaked more than expected and, combined with all those additional transistors, resulted in high power consumption and high operating temperatures. Prescotts soon became known as blazing-hot power-sucking hogs.

To make matters worse, at similar default clock speeds, the older Northwoods often matched or beat the new Prescotts in popular benchmarking tests. Experts speculated that although the longer Prescott pipelines would allow CPU clock speeds to eventually scale up nicely, the downside was slightly less efficiency at lower speeds. Detractors were quick to label it “Preshott” and proclaim it a failure. In reality, it was cutting edge technology that unfortunately had a few bugs because Intel had rushed the product to market.

It turns out that the Prescott does offer very good performance if overclocked high enough. At higher speeds, the Prescott begins exceeding the Northwood in many benchmarks. There are three main things to keep in mind when overclocking a Prescott:

1. Power Supply
2. CPU Cooling
3. Motherboard Cooling

Power Supply: Since the Prescott is power hungry, you need a hefty power supply to keep it happy. In other words, some generic 350 watt power supply probably will not be enough if you plan on overclocking a Prescott. Choose a good brand to use, such as the Antec True Power, Fortron, Enermax, Sparkle, or other reputable unit that can provide plenty of muscle and +12v amps. If you want a decent overclock, then do not skimp on a wimpy, cheap, power supply – invest in something decent.

CPU Cooling: Yes, the Prescott runs hotter than the previous Northwood; a ballpark figure is at least 10 degrees higher load CPU temp under normal conditions. The stock Intel retail cooler might be OK for default speed but is probably not the best for attempting high overclocks. However, it is possible to use the stock cooler for a modest overclock if you improve case ventilation and do the cooling duct mod as described later in this article. Most hardcore overclockers will toss the stock CPU cooler aside and upgrade to something better. The three most common types of Prescott cooling systems are as follows:

1. Air cooling
2. Watercooling
3. Phase change cooling

We will go into more details later.

Motherboard Cooling: Remember that Prescotts pull a lot of juice? Well, this extra power has to run through the motherboard circuitry, power regulator and mosfets. More watts mean higher temps. As overclockers already know, if we push the overclock high enough, we will usually need to bump up the vcore in order to increase stability.

Increasing voltage on a Prescott system heats up motherboard components more then some folks realize. Improving case ventilation is extremely important to control this extra generated heat. Socket 478 mobos were not really designed for all the extra power requirements of an overclocked Prescott. The i865 chipset mobos tend to be less desirable because of their smaller power mosfets. The i875 chipset mobos generally seem to have a more robust power circuitry.

From observations and personal experience, the two best socket 478 mobos are either the Abit IC7 series or the Asus P4C800 series. Regardless of which mobo you use, we recommend that you update to a newer BIOS that supports the Prescott and then perform some of the recommended cooling mods described in this article.
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If you compare a 2.8C Northwood to a 2.8E Prescott with both of them running at default speed, you would be unimpressed with the Prescott. But as the Prescott is overclocked to higher speeds, the performance scales up, especially memory bandwidth benchmarks and Super Pi scores. Apparently the doubled amount of L1 and L2 cache is finally starting to come alive at higher speeds. The challenge is coaxing enough of an O/C out of the Prescott to make it worth the extra cooling that is required. By the way, a Prescott system makes a great SETI cruncher or folding rig.

The first Prescotts released in February 2004 were the C0 stepping. Some improvements were made and then in June 2004, the D0 stepping was released. At the time of this article, the only readily available Prescott P-4 socket 478 D0 stepping is the 3.2E (s-spec SL7KC). Most of the D0 steppings appear to be going into the production of the socket LGA775 processors. Perhaps the Prescott C0 steppings did not sell as well as expected and Intel has excess inventory or maybe Intel wants us to abandon the socket 478 all together and move to the LGA775 platform?

Here are a few benchmarks that compare overclocked Northwoods vs. Prescotts that were personally done by one of the authors. The same computer system was used each time and only CPUs were changed.

System specs:

• Abit IC7
• 2 x 512 Hyperram PC4200 using SPD timings
• Swiftech watercooled Q-Power case
• Antec True Power 550w PS
• ATI 9700 Pro video card running at default speeds/settings

This was not meant to be a comprehensive review, but rather to just give a rough idea what to expect.

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Since the Prescott runs hotter than the Northwood, a good overclocker will probably want to figure out how to bring temps down, especially if you are using air cooling. Improving case ventilation is one proven method of keeping your overclocked system from going up in smoke.

Generally, the standard ways to start improving case air flow include adding a front intake case fan and a rear exhaust case fan, then tidying up power and data cables so they are not blocking air flow. Rounded IDE cables and SATA cables help improve ventilation compared to the old school bulky restrictive IDE ribbon cables.

Want to try a completely different case cooling mod to impress your friends? How about cutting a blowhole and mounting a fan to cool the backside of the motherboard? Check out this Overclockers.com article by Stan Slatten.

Apparently Intel recognizes and acknowledges that there are heat issues with this new breed of processors. Intel has a webpage describing a “Thermally Advantaged Chassis” (case) that is recommended for Prescott or Extreme Edition processors. To quote the Intel webpage:

“A thermally advantaged chassis can be recognized by a hollow tube attached to the side panel called a chassis air guide which has flared ends. This tube will funnel cool air towards the processor passively, without fans. Its reliance on the internal system fans to guide air across the processor and other system components is achieved through a ventilation hole within the side panel that is required in order to function properly.”

Basically, to construct Intel’s “thermally advantaged chassis”, all you need to do is to cut a hole in the side cover and add a duct. The Intel design just relies on the CPU fan to pull fresh air through the duct to the processor.

Being an innovative overclocker, you might want to take this one step further by mounting a fan on the side cover blowhole to force additional air flow into the case. Here is a step by step guide (see below) describing the case duct mod that co-author Dave did to his Prescott system to dramatically lower temps. This improved case duct mod is quite easy and cheap.

Either follow the guide to the letter or modify parts of it to suit your own needs. For example, you might want to use a 92 mm or maybe even a 120 mm fan, since larger diameter fans can move the same volume of air at a lower RPMs, resulting in less noise. Instead of a round duct, perhaps you might want to fabricate a square duct. Hardcore gamers might want to make a second duct leading to their video card GPU. You are only limited by your imagination.
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Materials needed for cooling duct mod:

1. 80mm fan (I chose an Antec high flow model)
2. 80mm fan grille (I used this to hide any raw edge)
3. 3 inch rubber drain pipe coupler (the size you choose will depend on the outside diameter of the fan that you buy, so make sure you check this first. My fan was 3 inches. I purchased my coupler at a home supply company. They should be available at any hardware store.)
4. Masking tape (I used this so I would not scratch my case)
5. 4 fan mounting screws

Tools needed for cooling duct mod:

Pencil, saber saw, drill, drill bit, and file.

Instructions for cooling duct mod:

1. Tape up the side cover where you are going to be cutting the hole
2. Find the spot in the side cover that is directly over the CPU and mark it with a pencil
3. Remove the case side cover
4. Place the fan grille over this mark and trace around it
5. Drill a starter hole in the center of the marks that you traced around the grille cover
6. Cut out the hole that you just marked making sure you cut about 1/8 of an inch to the inside of the marks. That way, the grille will cover the hole opening, so you won’t have to worry if the cut is not perfect
7. File the edges to clean it up
8. Put the fan grille back over the hole, mark, and drill out the fan mounting holes
9. Mount the fan to the side cover. Make sure it is blowing air into the case
10. On the backside of the fan cut off the unused mounting lugs, this will in effect make your fan round allowing you to slip the pipe coupler over it
11. Slip the pipe coupler on the fan (can use a worm gear automotive hose clamp if you want to mount the coupler securely)
12. Cut the pipe coupler 3/8 of an inch from the CPU fan
13. Plug in the fan and reattach your side cover

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Presto, one happy cool Prescott! I know that these instructions seem long, but the whole thing only takes 15 minutes to complete. Just be careful with the side cover as it is made out of thin metal and cuts very easily, so it is easy to take off too much. It is better to cut the hole too small than too large.

(NOTE: the “after” temps at default 2.8 gig speed were never measured)

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Now that you have better case ventilation, you might want to consider doing a few mobo mods.

Why not slap some little heatsinks onto those hot power mosfets? You can order some pre-made sinks that will fit (Microcool makes nice mini-sinks) or you can dig around in your junk box and cut down some chipset sinks or an old CPU sink to recycle them into mosfet sinks. Install them permanently with a thermal conductive epoxy like Arctic Silver adhesive for best results.

Another option is to use thermal paste in the middle of the sink and a dab of super glue on each corner. If you want to be able to remove the sinks at a later date, you can just use thin double-sided thermal tape. Once the mosfets are sinked up, why not go for the gusto and sink up the PLL chip (clock generator) and southbridge chip? While you are on a roll, might as well improve the northbridge cooling too. Thermaltake and Swiftech make decent N/B coolers that easily clip right on.

Here is a pic showing sinks that were added to an Abit IC7-G mobo by one of the authors. The red arrows point to mosfet sinks, the yellow arrow points to PLL chip and the blue arrow points to the southbridge sink:

If you plan to air cool the Prescott and are looking for a respectable O/C, then certainly consider investing in a good heatsink and high CFM fan. It is tough to find a better heatsink than the well built, solid copper Thermalright SP-94.

Pair up your favorite heatsink with a high CFM fan that will move a ton of air. A 92 mm fan has larger blades that will move more air at the same RPM than a 80 mm fan. The higher the RPM, the noisier the fan. An adjustable fan like the 92 mm Enermax or a high speed fan like the 92 mm Tornado, combined with a fan controller unit, will allow you to crank it up to max speed if you are running hot during a gaming frag-fest or slow it down if you are just surfing the net. We encourage reading a few heatsink reviews prior to spending your hard earned cash.
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Watercooling works well with Prescotts.

The main drawback to watercooling is the added expense. The “right” watercooling setup will generally cool better then high end air cooling. If done correctly, there is very little concern about problems. However, there is always a slight risk of a water pump seal failing or a hose leaking. Of course, with air cooling the CPU fan can stop working too, so anything can happen regardless of what equipment used. Another bonus to watercooling is the quietness. Let’s face it – a noisy, high speed CPU fan that sounds like a vacuum cleaner gets old and annoying after a while.

Watercooling a Prescott does not mean you can throw away the case fans (you still need good case ventilation), but it does eliminate the CPU fan which tends to be the worst noise offender. You need fans to move air through the radiator too, but usually you can use quieter 120 mm fans for that job. If you watercool the video card and/or northbridge chip, then you can also eliminate one or two more fans. Another advantage of watercooling is the high “gee whiz” factor that will surely impress your friends and family.

If you are not experienced in watercooling, it can be a little daunting at first. But it really isn’t that hard. There is a ton of info available out on the internet. If you decide to try watercooling, don’t skimp on cheapo stuff or flimsy tubing. If you want more info about watercooling, go to the Watercooling Forum section of Overclockers.com (there is also a watercooling sticky post section that I would highly recommend) or surf Overclockers.com Watercooling articles and do a little research.

Watercooling the Prescott will not miraculously give you a huge overclocking improvement by itself. While it is better at cooling the CPU and quieter than air cooling, do not forget that Prescotts still sucks a lot of power through the mobo circuitry which produces heat. So, good case ventilation is still required and if you plan on pushing your overclock to the limits, then you might still need to add sinks to the mosfets, as discussed earlier in this article.

Phase change cooling (such as the Prometeia or VapoChill), peltiers, chillers, dry ice, and liquid nitrogen are all examples of extreme cooling. Remember – the efficiency of semiconductors improves with decreasing temperatures. More info about these forms of extreme cooling can be found in Overclockers.com’s Extreme Cooling Forum section. However, this article is primarily interested in fast, stable, reliable computers that can be operated on a daily basis on a reasonable budget; thus, we will leave extreme cooling for another article.

For the experienced overclocker that loves a challenge and does not mind doing a little extra work in the cooling department, overclocking the Prescott can be rewarding. The extra cache of the Prescott provides more performance at higher overclocked speeds. Reports are trickling in that the Prescott performs a little better than the Northwood in the Doom3 game.

Average Prescott overclocks for mid-year 2004 with air cooling are 3.4 to 3.6 gig, 3.6 to 3.8 gig with water cooling, and 4 gig or more with phase change cooling. If you get newer stepping Prescott plus add good case ventilation and do the cooling mods outlined in this article, then maybe you’ll get much more than an average overclock. Good luck!

Bryan Bain and Dave Casole