11:18 AM
Fred Langa
Fred Langa

The Explorer: None Like It Hot

Excessive heat is a CPU's worst enemy. Here are software utilities that can help.

Have you ever touched the surface of a working computer's CPU chip -- say, a Pentium or an Athlon? These days, they get hot enough to take off your fingerprints.

Fortunately, it's not that easy to touch the surface of a working central processing unit: Almost all CPUs are covered with heat-sink-and-fan assemblies that help dump the chip's heat into the air inside your computer's case, from which it's vented out by one or more additional fans.

You see, heat is the enemy of a CPU chip. The cooler a CPU chip is kept, the more stable it is and the longer it lasts " it's as simple as that. At abnormally high temperatures, a CPU may behave erratically or lock up; if you're lucky, normal operation will resume when things cool off. But a single extreme temperature spike, or long, frequent periods of running "outside thermal spec," can permanently damage or destroy a CPU.

Thermal management in personal computers -- and CPUs in particular -- used to be a fairly forgiving science with a wide range of acceptable, roughly-engineered solutions. Early PCs had one fan inside the power supply, for example, to handle cooling for the entire system. But as CPUs got faster and more advanced, they pumped more and more energy through smaller and smaller wire traces at ever-increasing clock frequencies. The result is that today, without properly-sized and functioning heat sinks and fans, most CPUs would literally cook themselves to death in short order.

That's why so many current desktop PC designs internally resemble miniature wind tunnels: The higher-end and faster your PC, the more fans it's likely to have.

The 1.2GHz PC sitting at my feet, for instance, has no less than five fans busily whirring away: a very large fan ventilating the case as a whole, a smaller fan ventilating the power supply (and, to a lesser degree, the case), a medium-sized fan blowing air down through the CPU's massive heat sink, and a pair of tiny fan/heatsinks mounted on other chips -- one on the video card's graphics processor, and one on the motherboard's largest chip.

Although the main focus of this article is desktop PCs, laptops also can run hot, but usually not as hot as full-sized desktop units. That's because laptops use special lower-voltage components and aggressive power-saving technologies, and usually run at lower speeds than top-of-the-line desktop models. Many laptops can get by with smaller fans, or even no fans at all (as can some special desktop designs). One common trick laptops use is to dissipate heat through the laptop's housing, using the metal case as a heat sink -- often to the chagrin of travelers on long-duration plane flights, who find their thighs getting singed by the excess heat pouring out through the bottom of their laptop.

Problem Areas
While there are exceptions, most PCs from major vendors start their lives reasonably well-ventilated and are able to keep the CPU chip and other components within thermal specs -- as long as the fans keep turning and the airflow remains unobstructed.

But many vendors use cheap fans with relatively short lives: If a fan dies on you, your first warning might be a general and seemingly-inexplicable system failure.

Or, if you don't clean the inside of your PC from time to time, the air intakes may become clogged with dust, dirt and pet hair, leading to overheating and trouble. (This will only sound weird to you if you've never opened the case of a PC that has been allowed to run undisturbed and uncleaned for a long time. The amount of crud that accumulates inside a PC case can be truly amazing -- and disgusting!)

Some system vendors also have been known to cut corners, producing PCs that are technically within thermal specs, but running far hotter than they need to. This puts unnecessary stress on the system and all but ensures a shorter system life.

And if you modified your system by adding a new component (say, a new CD drive), your placement of cables and connectors could interfere with the airflow, possibly causing localized overheating.

A bit further afield, if you built your own system from scratch or replaced the CPU, it could be hard to know if you chose the right combination of fans and heatsinks.

So the question is this: How can you tell if your system is properly cooled? How can you tell if the airflow is right for your PC? How can you tell (without opening the case) that all the fans are turning? How can you tell that your PC isn't susceptible to erratic operation or even premature death caused by too-high or barely in-spec temperatures?

Learning From The Overclockers
"Overclockers" are people who push their CPUs to speeds way beyond their rated capacity. In fact, overclockers often compete among themselves to see who can run a given chip the fastest -- the PC hardware equivalent of automotive hot rodding.

In running their chips far out of spec, overclockers face major thermal problems: The loss of CPU cooling for even a second or two (!) can totally fry a highly-overclocked chip beyond recovery. As a result, the overclocker community has developed many heat monitoring and management tools and techniques. 

With today's hot-running standard chips, many major-brand system vendors have adopted some of the overclockers' tools and techniques to help cope with thermal issues in their off-the-shelf, higher-end systems.

For example, many of today's motherboards (maybe yours!) now come with built-in sensors to keep track of things like fan speed, and system and CPU temperatures. Sometimes, the sensors are tied to a basic alarm: If the system gets too hot, an alarm sounds. Other more sophisticated systems allow direct reading of this information through either the BIOS setup program, or via special software. But this software is almost never included as part of the base system. Even if your system has these advanced sensors built in, you may not know that they're there, or be able to access the information they can provide.

But there's a ton of software on the Web, if you know where to look. Some of this software is specific to one brand or type of motherboard; other programs support many brands and models. For a taste of what's available -- much of it free, thanks to the overclocker community (bless 'em) -- poke around in Tweakfiles.

I've tried some of that software myself. For example:

Motherboard and CPU Monitors
Perhaps the best-known and most widely-used freeware thermal monitoring tool is called simply Motherboard Monitor (or MBM).  When you run it on a PC equipped with the appropriate thermal and fan sensors, it will show you the information it collects in the Windows system tray. It also can sound alarms or launch corrective actions (e.g. shutting down) in the event it detects an out-of-spec reading.

The MBM site will give you all the info you need, including whether or not your system can use it. But it's not highly polished, and you can expect to have to do some digging to find out what options you have.

(The MBM site is also a good place to find out the maximum recommended temperatures for your particular CPU. If your specific brand, type and model of CPU isn't listed there, you can try the HeatSink Guide, or go to the home pages of your CPU vendor and search their technical literature.)

While MBM is good, I've come to prefer the look and feel of a slightly different freeware tool called MBProbe. According to the site, it

"...monitors voltages, temperatures and fan speeds using hardware monitoring chip(s) available on many modern motherboards. Its features include:

  • Up to 9 voltage, 4 temperature and 3 fan speed readings (subject to the limitations of hardware monitoring chip(s) present).
  • Automatic detection of monitoring chips.
  • Small memory footprint.
  • Setting of nominal voltage and fan speeds with warning thresholds.
  • Setting of temperature warning limits and offset readings.
  • Setting of sensor used for each temperature reading.
  • Temperature display in Celsius or Fahrenheit.
  • Customisable task when critical temperature is exceeded for more than 30 seconds continuously.
  • Ignores fan warnings for 10 seconds after system comes out of suspend.
  • Swappable temperature display in status icon on taskbar.
  • Event and history logs."

I have it running in my system tray. The display alternates between showing my CPU temperature and the motherboard temperature, and I have it set to sound an alarm if the temperatures, voltages, or fan speeds drift outside safe ranges.

Like MBM, MBProbe is a little awkward to set up correctly. But once it's running, it's unobtrusive and kinda cool. Right now, for example, I know that my CPU and motherboard fans are both spinning within a few RPM of their rated speeds; the motherboard is well-cooled and running just a couple degrees above room temperature; the CPU also is well-cooled, running almost 60 degrees C (or about 100 degrees F) below its rated "safe maximum" temperature; and the power supply is delivering nominal voltages.

If I stress my PC -- say, if I start a long download while burning a CD and also doing routine office tasks -- I'll see the CPU and motherboard temperatures climb modestly, although never even remotely close to danger levels. (Another sign of good cooling.) What's more, when the workload goes down, the CPU temperature falls almost immediately, which also is an indication that my system's heatsink, fans and airflow are all properly sized and working as they should.

So this simple kind of system monitoring can show you very quickly whether your system has a serious thermal problem or not. And beyond that basic, initial OK/Not-OK assessment, I also feel better knowing that the software is keeping an eye on things on an ongoing basis. If a fan dies, or the airflow becomes obstructed, or if my power supply starts to drift out of spec, I'll know about it and can take action before any damage can occur.

If It's Not OK: Cooling Options
My system was OK. But what if you should find that your system isn't OK?

First, open the case and look for dead fans or airflow blockages (dust, poorly-routed cables, etc.). If those aren't the problem, then your fan/heatsink combination may not be OK. A source like Tom's Hardware Guide can lead you to a world of custom hardware-oriented cooling solutions.

But there also are 100 percent software solutions for CPU cooling. Some operating systems (including Windows 2000) have this software solution built in, but Win9x does not. The cooling trick is the use of an HLT (or "halt") instruction during idle times. Stopping the CPU instead of letting it idle at full speed helps keep temperatures down.

And by "idle times" I don't mean when the PC goes to sleep. Consider that, when you're typing, a quarter second might pass between consecutive keystrokes. If you have a 500 MHz processor, that means that from one keystroke to the next, your CPU twiddles its thumbs for 125 million cycles (even more for faster processors). If many or most of those cycles can be shut off, your CPU will stay cooler.

Of course, there's more going on inside any PC than just waiting for keystrokes, and the more multitasking that's going on, the fewer idle cycles there are for a CPU-cooler app to work on. Results vary widely, depending on how you use your PC, but the theory is sound: The more idle cycles there are, the more an HLT command can help.

(Interesting side note: A CPU that's HLT-ed also saves power, so this approach has energy saving benefits that can be useful on a desktop, and very significant on a battery-powered laptop.)

You can find many free and low-cost CPU cooler software utilities via any search engine, such as this Google search.

But here are some of the more well-known ones:

And there are more reviewed and rated at Benchtest.Com

Diminishing Returns
There's a ton of evidence that CPU coolers help a lot on systems that run hot, but I didn't know what I'd see on my system because MBProbe had already shown that my CPU is extremely well-cooled to start with. And in fact, none of the cooler software I tried produced any noticeable results at all.

But I took this as a sign of success, not failure: With my system's already-excellent mechanical cooling (via airflow) there just wasn't much left for these software-only coolers to do. It was further proof that the engineers who designed my system did their homework well.

Related resources:

Max. Allowable CPU Temperatures


Software CPU Coolers and Related Tools

Software CPU Coolers Rated

Hardware CPU Coolers Rated

With that reassurance, I uninstalled the CPU cooler tools, but left MBProbe running. It's a permanent addition to my system tray to help make sure that my system stays thermally healthy for what I hope will be a long life.

No Surprises
In a perfect world, we'd never have to think about heat issues in PCs: All vendors would design their systems well, fans would never die, dust would never choke off a system's airflow, and everything would work perfectly.

I'm not holding my breath waiting for that perfect day. Instead, I'll run a small, free monitoring tool to keep an eye on what's going on inside my PC, and if I need to, take steps via software or hardware to correct any problems that arise.

What about you? What monitoring or cooling tools have you tried? What results have you gotten? What heat-related problems have you seen? Join in the Discussion!

To discuss this column with other readers, please visit Fred Langa's forum on the Listening Post.

To find out more about Fred Langa, please visit his page on the Listening Post.

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