Chip cooler round-up!

Review date: 24 October 2000.
Last modified 03-Dec-2011.


Modern PC CPUs are generally rated to operate with a quite wide range of die temperatures - the temperature of the actual processor silicon inside the chip package. Current Socket A AMD Athlons, for instance, are good for a 0 to 90 degree Centigrade temperature range.

If your CPU's core temperature gets higher than its rated range, you'll have a flaky computer. You're not likely to actually damage the CPU - modern small-die processors can occasionally cook themselves, but only if they're run with no CPU cooler at all - but a computer that falls on its face every half-hour may well be damaged in a much more dramatic way by its frustrated user.

For most purposes, low performance "stock" CPU coolers are perfectly adequate. Boxed Intel Socket 370 CPUs come with neat and easy-to-install coolers. But at the moment there might as well be no such thing as a retail-boxed AMD CPU - everybody just buys the same Original Equipment Manufacturer bare chips as are used by system assemblers - so if you buy one of those, you have to buy a cooler with it. And there's no harm in getting a chunkier-than-normal one.

And then, there's overclocking. If you're one of the merry few that run your CPU faster than stock, a good-sized cooler is an essential accoutrement. Modern CPUs actually run cool enough that just scraping the cheapo thermal pad off a stock cooler and replacing it with a smear of heatsink grease is enough to deal with many processors' cooling needs. But when you're really increasing the heat output by goosing the CPU voltage to make it stable at an elevated core speed, another few bucks for a big cooler's a small price to pay for the performance of a processor five times as expensive as the one you bought.

And some people need CPU cooling in odd places - rack-mount computers, and other cramped cases.

Assorted CPU coolers!
Clockwise from bottom left: Thermaltake Blue Orb, Thermaltake Chrome Orb, Kanie Hedgehog 238M, Just Cooler P-925, Alpha PAL15.

For all of these reasons, after-market coolers may be for you. And since many of them are pleasingly cheap, there's no harm in getting a shiny show-off cooler to go with your new CPU even if you don't intend to run it faster than normal. Particularly in Australia, it never hurts to have a bit more cooling.

I've checked out a couple of low-cost pretty-coolers, a super-slimline unit, a teeny one for things other than CPUs, and a solid copper monster for when too much heatsink is barely enough. On with the show!

Blue is beautiful

Just Cooler P-925

Just Cooler is a Taiwanese company that makes a variety of airflow-related computer gadgets, and their P-925 is a good-sized chunk of anodised aluminium, considering that it costs only $AU22 delivered.

Just Cooler P-925 base

The bottom of the P-925 has a factory-applied square of thermal transfer compound (or, to use the technical term, "goop") on it; you just remove the clear plastic guard and squish it down onto your CPU.

Tweakers will want to wipe off the stock compound and replace it with a much thinner smear, but for less demanding applications this is a simple cooler to install, and should get good contact. The clip's a slightly awkward hinged-ratchet type, but holds the cooler properly on Socket 370 and Socket A CPUs - and probably old Socket 7 and Super7 chips (Pentiums, K6s...) as well.

The Just Cooler 0.84 watt low-profile fan's no wind machine, but it's a three-wire unit that reports its speed to the motherboard, and it gets the job done.

As a low cost, nice looking, easy to install cooler for a stock-speed or mildly overclocked CPU, the P-925 should do well. And it ought to fit on practically any motherboard, too; its cantilevered shape means it clears the power smoothing capacitors that closely surround the CPU socket on many boards.

Just Cooler's page for the P-925

Round. Shiny. Cute.

Chrome Orb

This is the Thermaltake DU0462 "Chrome Orb". It shares the radial-fin design of the other Orbs, which was... borrowed... from the much more expensive Hewlett-Packard TurboCooler, which begat the current Agilent ArctiCooler, which is by all accounts not quite ready for prime time in the retail market yet.

The radial-fin design, whoever makes it, uses a relatively low-power fan and fins arranged for low air resistance but lots of air flow. Even Thermaltake's bargain-basement version of it works as well as a considerably heavier conventional heat sink and fan.

Earlier Orbs had a nifty twist-clamp locking mechanism that worked very well with Socket 370 CPUs, and could kill Socket A ones stone dead in one twist. Thermaltake flailed around a bit trying to come up with a better clip design, and they've settled on the Chrome Orb's stiff springy piece of metal, which isn't the easiest clip in the world to attach, but also isn't going to snap your AMD processor like Pocky.

The Orb sticks out enough around the socket to make it a bit of a tight fit on many motherboards. It only actually fouls the power capacitors on at one board that I know of, the Abit KT7 (reviewed here). A brief assault with a grinder solves that problem.

Chrome Orb base

The base of the Chrome Orb has pre-applied thermal compound with the consistency of chewing gum left on the bedpost for about a week. You peel off the backing plastic before you install the cooler, and you'll need to scrape the cooler clean and put grease on it if you want to remove it and use it again.

At $AU36.30 delivered, this is a mid-priced cooler, but it's still cheap compared with even bargain basement CPUs, and its performance is good. Not as good as its space-age looks might suggest, but good enough for most purposes.

Thermaltake's page for the Chrome Orb

Alpha slims down

Alpha PAL15

Alpha make very well engineered and surprisingly reasonably priced CPU coolers with top-notch performance. But the average Alpha cooler's a big blighter. It, and practically any other CPU cooler, isn't going to be suitable for use in a really cramped case, like one-unit rack-mount computers or other low-profile systems.

Of course, most rack-mount computers don't need a big CPU cooler, because they run weedy CPUs. An old 486 is fine with a plain heat sink (and no fan), as long as the case it's in has good enough air flow.

If you want to build low-profile PCs with modern CPUs, though - and with Celerons and Durons as cheap as they are, it's a very tempting prospect - you'll need a decent cooler that takes up as close to no room as possible.

The PAL15, which is selling for around the $US30 mark, addresses this need. Bottom to top, it's only about 28mm in height, including the heads of the fan mounting screws. It's slightly smaller than one of the 60mm fans that come with other Alphas.

FC-PAL15 base

Like the other current PAL series coolers, the PAL15 has a copper heat spreader inlaid into the base of the heat sink. The spreader helps to couple the small contact point of modern processors to the large radiative area of the heat sink.

All current PAL-model Alphas, including the PAL15, have four plastic feet on the bottom of the heat sink to help keep the cooler stable on modern small-die Intel CPUs. The older Plastic Pin Grid Array (PPGA) Celerons have a much larger contact point; old-style coolers used on FC-PGA chips can wobble around and fail to make good contact.

The Alpha baseplate design should work fine with all current Socket 370 and Socket A processors - P-III, Celeron, Duron and Athlon. The AMD CPUs have rubber dots on top to keep coolers stable; the Alpha plastic feet don't interfere with them.

Low-profile cooler comparison

Here's the PAL15, on the left, compared with the special slimline cooler that comes with the PC Chips Book PC I review here. I was never very confident about the capabilities of the little PC Chips cooler; I think the Alpha cooler would fit in its place, and if you're building a high speed Book PC, it'd be a good idea.

The PAL15's fan's very slim indeed, but it moves about the same amount of air as the fatter fan on the Just Cooler P-925. You wouldn't believe that just looking at the manufacturers' specs, though.

Alpha rate their fan, mounted on the heat sink, as being good for 0.37 cubic metres per minute (about 13 cubic feet per minute) of airflow. Just Cooler rate their fan at about 0.5 cubic metres per minute, but that's an unqualified figure, which means it's probably "free-air" - how much air the fan can move when it's just hanging there in space. Put it on the heat sink and your air flow drops.

PAL15 kit

No Alpha coolers come assembled; you get it as a box of bits. It's easy for anyone with a screwdriver to put the processor together in a couple of minutes, though.

The PAL15 is particularly easy to assemble, because there's no air-guiding shroud over the heat sink. All of the larger Alpha coolers use a shroud to increase their efficiency.

It's easy to install, too, because it uses the same swing-clip attachment gadget as all of the other socket-CPU Alphas.

You get a little tube of heat sink grease with the cooler, and the instruction sheet tells you what to do, in English.

This isn't a cooler for the rabid overclocker. It'd be fine for stock-speed basic computers, but you can get a bigger cooler with the same performance for less. Alpha quote the PAL15's thermal resistance as being up around 0.8 degrees Centigrade per watt, versus less than 0.4 degrees for bigger Alpha socket-CPU coolers.

For a cooler as small as this one, though, the PAL15's a gem.

Buying one

Alpha are in the happy position of being able to sell CPU coolers to distributors faster than they can make them, and so they've discontinued their online shopping service for the time being. This means you've got to buy their coolers from resellers. There's a list of them here.

Alpha's page for the PAL15

Rare metal

Hedgehog 238M

The Kanie Hedgehog 238M is a CPU cooler for people who reckon that Alphas just aren't extreme enough.

My Hedgehog came from Cool PC here in Australia, who have as I write this sold out of them, but more will presumably be on the way soon. The 238M's $AU79, which is not very much more expensive than a similar-shaped Alpha, especially if you have to buy that Alpha from overseas.

The Hedgehog's basic design is very Alpha-esque - lots of tall pins, shroud, big fan sucking air through the heat sink - but that heat sink's not made of aluminium. It's made of copper.

The aluminium used for almost all PC heat sinks (usually some flavour of 6063 alloy, for the metalworkers out there) is strong, light, not terribly expensive and has good thermal and electrical conductivity.

But aluminium only has about half the thermal conductivity of copper, which is about as good a thermal conductor as silver. Higher thermal conductivity lets heat get from the CPU contact patch to the whole pin surface area more easily; the better your thermal conductivity, the better your heat sink cools the CPU.

So why aren't all heat sinks made of copper? Well, copper's structurally lousy - either very soft, or too brittle to be used for heat sink pins, depending on how it's treated. The Hedgehog's made of soft copper, and comes with a stern warning about not grabbing its heat sink by the pins, lest you bend them.

Copper's also very heavy. Make the exact same heat sink out of copper instead of aluminium and it'll weigh about 3.3 times as much. The Hedgehog 238M weighs a hefty 445 grams all told. That's almost a pound!

The weight of the thing makes it a dodgy proposition if you're installing it on a CPU in a "slotket" adapter card, to let you use Socket 370 processors on older Slot 1 motherboards. That much overhanging weight puts a lot of strain on the CPU mounts, which in many slotkets are pretty slapdash affairs.

Not that many people don't install Gargantuan hunks of metal on their Slot 1 or Slot A CPUs - Alpha's P7125M60 for Slot A Athlons and old-model "SECC" Intel CPUs is an aluminium monster that weighs more than the Hedgehog. But it mounts on a full processor cartridge, not a flimsy slotket.

Hedgehog kit

Like the Alpha coolers, the Hedgehog comes as a kit. And, like the Alpha kits, this one's very easy to put together. It comes with the same sort of clip as the Alphas, too, which makes it simple to install once you've built it.

The Hedgehog comes with a high-output Y.S. Tech fan, which shifts about 50% more air than the Sanyo Denki fans that come with the larger Alphas.

The Hedgehog heat sink comes shrink-wrapped, to keep it shiny and un-corroded. Corrosion on the pins shouldn't make much difference to anything, but a layer of oxide on the bottom of the sink would impede heat transfer.

Hedgehog heat sink

Pretty, ain't it?

The Hedgehog has a plain flat base plate, with a rebate for the end of the Zero Insertion Force socket that contains the cam-activated CPU locking mechanism. This means I'd be a bit nervous about using a Hedgehog with an FC-PGA CPU, especially if the motherboard was going to end up mounted vertically, rather than horizontally. All of that weight bearing down on one edge of the CPU core could do it a mischief.

Fortunately, there's something you can do about this problem. Shim your CPU. A square of metal just the right size between CPU and cooler, with cutouts for the CPU core and any other top-of-chip components, takes the strain off the core. And Cool PC also sell shims for FC-PGA and Socket A CPUs.

Socket A shim

Socket A CPUs are much more fragile than Socket 370 ones. The top of the CPU, on which the cooler sits, has similar physical properties to a little bit of glass. Get your cooler installation wrong, and it's easy to bust off a corner of the top of the CPU.

This seldom actually kills the chip, but it's disturbing, especially if you fail to clean up the fragments properly and grind little bits of glass between the cooler and the CPU on your next mounting attempt.

The four little rubber dots stuck to the top of the Socket A CPU package aim to reduce this problem; they stop you from getting your cooler too far off level. But they're not perfect.

This Japanese-made copper shim aims to solve the problem, by giving the cooler a much larger contact area.

The hole in the middle is for the CPU core; the slots around it are for the little surface mount components on the top of the chip package.

Cool PC sell the shims for $AU29.

They also have simple, Aussie-made shims for Socket 370 CPUs. These only need the one rectangular hole in the middle, and cost a mere $AU5.

The Hedgehog and shims came from Cool PC.

Kanie's Hedgehog 238M page

Baby blue

Blue Orb kit

The TGF020 "Blue Orb" is another Thermaltake product, and it's based on the same radial fin design as the bigger Orbs. It's only about 5.5 centimetres in diameter and about two centimetres high, though, and it's meant to be used to cool motherboard northbridge chips (the ones that usually get a little green passive heatsink), graphics card main chips, and so on. It costs 4AUD27.50, delivered.

Putting a better heatsink on a motherboard chip isn't a bad idea if you've got one that runs hot - dual processor boards, in particular, stress the northbridge more than it may like. And, again, overclockers need more cooling - if you're running higher-than-normal Front Side Bus speeds, the northbridge heats up.

Motherboards that use the normal little-green-heat-sink on their northbridge chip hold them on with a couple of simple spring-loaded split-pins, which are quite easy to remove and replace with a pair of pliers. It's not a bad idea to pop the stock heat sink off and add a dab of thermal grease under it, even if you're not going to do anything else; most of the green-sinks are put on "dry" and so achieve very little.

Many video cards also have a couple of cooler mounting holes on either side of their main chip, even if they don't actually use them for anything, and just have a cooler stuck on with thermal cement or, more commonly, thin high-conductivity double sided tape.

It's seldom very difficult to remove even bonded-on coolers; a flat-blade screwdriver to lever it off, and a piece of cardboard to protect the board from damage, usually does it.

Blue Orb base

The Blue Orb gives you a couple of mounting choices. The best method is using the supplied pair of spring-pins.

The holes in the Blue Orb base for the spring-pins are about 55 millimetres apart, which comes fairly close to matching the hole spacing on various motherboards and video cards. There's enough wiggle in the pins that you can tilt them in or out to match slightly different hole spacing.

There's a little plastic pack of thermal grease in the Blue Orb package, too, for people that use the pin mounting.

If the pins don't match the thing you're putting the Blue Orb on - its holes aren't spaced appropriately, or it has no holes at all - there's a square of double-sided thermal tape included, too.

Thermal tape's touchy stuff - for decent conductivity, it needs to be very thin indeed, which makes it easily damaged - but a decent-sized square of it like this isn't too hard to deal with. Of course, if you want to re-use the Blue Orb, you'll need more tape.

The Blue Orb has a three-wire speed reporting fan, but it also comes with a four pin Molex plug passthrough power adapter, which lets you use it in systems without a spare three pin header. Using the adapter means you can't monitor the fan speed, but it makes the cooler useable in anything with a standard PC power supply.

Joe Average doesn't need the Blue Orb. But if you've got a basic-model video card that comes with just a passive heat sink and no fan, a Blue Orb may let you crank its speed up considerably further than you could with the stock hardware. And it should do a better job of keeping motherboard chips cool than the usual solution to the problem - just sticking a dinky fan on top of the plain green heat sink.

Plus, of course, it looks cool.

Thermaltake's page for the Blue Orb

Further reading

In case you are seized by a perverse and terrible desire to know more about the electrifying field of processor cooling, check out my piece on how to install coolers properly, here. For light relief, the article on CPU water cooling here may amuse you. And don't forget my piece on how to fit a Big Serious Fan to your PC case, which is here.

Buy CPU coolers!
Readers from Australia or New Zealand can purchase all kinds of CPU coolers from Aus PC Market.
Click here!
(if you're NOT from Australia or New Zealand, Aus PC Market won't deliver to you. If you're in the USA, try a price search at DealTime!)


Figuring out how well a CPU cooler actually performs is not an easy task.

For a start, case airflow is important. Since all of these coolers are just a fancy chunk of metal with a fan, they can't possibly cool the CPU down below the temperature of the ambient air.

You can cool CPUs to below ambient temperature, by using solid state Peltier effect heat pumps or a vapour phase refrigeration system, but active cooling systems like this are not for the faint hearted. Even if you're using active cooling, you still want the air inside the case to be as cool as possible.

To achieve this, you need a well ventilated case. Most cases can accept an extra fan or two, server cases commonly have an army of fans, and there's a whole hobbyist scene centred around cutting "blowholes" in cases for more throughput. But there are squillions of possible case configurations (counting all the gadgets inside as well as the fan setup), and every one moves different amounts of air. And the air temperature varies with the weather, anyway.

Assuming you've decided on one particular ambient air temperature with which to test your cooler, and ignored the fact that more effective coolers in real cases reduce their own efficiency slightly by heating the air inside the case, you then need a way to tell how hot the CPU actually gets.

You don't care about how hot the heat sink gets. You don't care about the temperature of the air that blows out of it. You don't even care about the temperature of the CPU's plastic packaging. All you care about is the temperature of the CPU core.

AMD CPUs don't have an internal temperature sensor. Many Athlon and Duron motherboards, both Socket A and Slot A, can measure CPU temperature - but what they're really measuring is the temperature of a sensor stuck onto the processor heatsink in a with-any-luck-representative spot, not the temperature of the inside of the processor package itself.

A few Socket A boards have a sensor under the CPU, in the middle of the socket. That's a bit better, but the temperature of the sensor still doesn't even have a linear relationship with the core temperature. This is because the heat sink efficiency changes with the difference between its temperature and the ambient air temperature, while the amount of heat energy the CPU has to dispose of doesn't have anything to do with the ambient temperature.

A CPU cooler thus gets better and better at shedding heat as it gets more and more heat pumped into it. Give it twice the energy to dispose of, and any given part of the heat sink will be less than twice as hot.

If you don't know what the relationship between sensor temperature and CPU temperature is - and you don't - then you can't say what a particular temperature reading really means, even if you know the air temperature. And you certainly can't compare readings between different computers. Fortunately, Intel CPUs do have an internal temperature sensor. It's not right slap bang in the middle of the processor die, but it gives an accurate and repeatable number that's about as good a temperature figure as you're ever likely to see.

So getting performance figures for different coolers should be easy, right? Clip the thing onto an Intel chip, make the computer do some onerous and repeatable task for a while until the temperature plateaus, and take a reading, yes?

Well, no. Because there is no standard "clip", and there is no standard task, either.

Different coolers have radically different clip designs, some of which hold the cooler down very tightly, and some of which don't. The greater the clamping force, the better the thermal transfer. This makes a big difference.

So does the thermal interface material - the stuff between the heat sink and the CPU. There has to be some kind of thermal interface material, because otherwise there'll be lots of microscopic air pockets between the imperfectly flat top of the CPU and the imperfectly flat bottom of the heat sink. Under high magnification, even apparently super-smooth surfaces look like sandpaper. This makes for crummy thermal conductivity.

Ideally, the interface material should fill all of the air gaps and not interfere at all with the actual metal-to-metal contact. In reality, this isn't possible; even the lightest smear of heatsink grease will reduce the effectiveness of the metal-to-metal contact, although filling the air gaps means that, on the whole, it helps. The thicker and less conductive a thermal interface is, the lousier will be the heat transfer. Since air is roughly 8800 times less thermally conductive than aluminium, this matters.

Low-performance coolers come with some kind of thermal transfer pad stuck to the bottom of the heat sink. The pads are simple and re-useable, but they vary from average to awful in their thermal conductivity.

You can upgrade a cooler like this in a couple of minutes, by scraping off the pad and replacing it with a smear of heat sink grease, yours for not much from any decent electronics store. Properly applied heat sink grease gives you an excellent thermal connection. But it depends on how hard the joint is clamped, and you only need a very small amount of grease, if the surfaces are pretty flat to start with.

Of course, many coolers these days have some sort of pre-applied thermal goop that's better than a simple pad. The Just Cooler P-925 and the Thermaltake Chrome Orb are excellent examples - lots of pre-applied grease on one of them, a thin square of gummy stuff on the other. And the Blue Orb can be attached to a chip with tape or held down with spring-pins. And the spring-pins will hold with different strengths depending on the height of the chip and the spacing of the holes.

Scraping clean all of the coolers and applying a hopefully consistent layer of standard zinc oxide thermal grease would help a bit, but then you'd be testing how good they are when they're used in a way that most people won't ever use them.

Getting a CPU to pump out a steady amount of heat, at least, isn't too hard. Just make it run some number-crunching nothing-program like a prime number calculator, and a given type of CPU running at a given voltage and core speed will deliver a quite consistent heat output.

This isn't very elegant, though, because unless you've got ranks of identical machines, it means you can only test one cooler at a time. If the ambient temperature changes between tests, you'll need to factor it in. Plus, of course, using 30 million transistors to do the job of a toaster element is just... just wrong.

OK then; forget the CPU. Use a calibrated dummy load. A little power resistor like this one...

Power resistor

...for instance.

The body of this 4.7 ohm 25 watt resistor's only about 25mm long, so it could easily match the underside of a CPU cooler. Its 25 watt power rating's with only passive air cooling; with the extra cooling it gets from a CPU cooler, you could feed it 16 volts, for a 3.4 amp current and about 54.5 watts of heat output. That makes it about as hot as a 1GHz Socket A Athlon.

But a resistor is not a CPU. It has a different-sized contact patch. And it doesn't have a clip - you'd have to incorporate the resistor into a dummy CPU socket so the cooler could clip on, or give up and use some general purpose fixed-force clip.

All of this explains why I bought a card of ten little resistors like the one shown above, but haven't done a darn thing with 'em yet.

Making numbers is easy. Making meaningful numbers is a lot trickier.

Even without good performance measurements, though, it's possible to make a few judgements about the relative performance of different heat sinks, and once you know the basic rules it'll help you judge whether the yum cha sink on a given piece of equipment is worth sticking with.

It all has to do with air flow and surface area. More air flow - a more powerful fan - and more surface area - more fins, or pins - equals more cooling power, all things being equal.

Of course, the air flow patterns in a heat sink are complex, and changing the design to increase the surface area of the sink will also probably increase the air resistance, and reduce the air flow you'll get from a given fan.

The PAL-series Alphas have a staggered hexagonal array of 350 hexagonal pins, each of which has sides a hair over 1mm in width, so you get about 65 square millimetres of surface area per centimetre of pin height for each pin - an impressive 227.5 square centimetres of area per centimetre of pin height, for the whole 350 pin heat sink.

The FC-PAL15 thus manages only about 250 square centimetres of pin area, since its pins are so short, but bigger Alpha sinks like the PAL6035 manage about 750.

The Hedgehog sink, on the other hand, has a square array of 238 rectangular pins, about 2.1 by 1.5mm each. This gives you about 72 square millimetres of surface area per centimetre of pin height, or 171 square centimetres for the whole heat sink. With about 30mm of air-catching pin length and a little more for the two longer rows on each end of the sink, you get maybe 520 square centimetres of total surface area.

Since it's got a beefier fan than the similar-shaped Alpha, and is made of metal about twice as conductive, it ought to perform better.

The completely differently designed Chrome Orb has 60 fins, about 30mm of each of which sticks up into the airflow, with a total surface area of about 324 square centimetres. Its fan's much weaker than the ones on the expensive square coolers, but the radial fin design presents less air resistance, so that doesn't matter too much.

For comparison, the black finned heat sinks that come with boxed Intel Socket 370 processors at the moment have a total fin area of about 260 square centimetres - and a dinky little slimline fan that moves less air than even the Orb's, much less the larger coolers.

Give Dan some money!
(and no-one gets hurt)