Heat

Q. How much heat does the 6x86 processor produce?

A. The 6x86 processor can dissipate as much as 25 watts of power depending on the CPU clock frequency. This is an amount comparable to the Pentium Pro processor. The case temperature range for the 6x86 processor is 0°C-70°C (32°F-158°F) - the industry standard commercial temperature range for all electronics devices. When design specifications are followed the 6x86 processor works properly over the specified operating temperature range.

The 6x86 processor package is cooled by radiation, convection, and conduction. This is achieved with a heatsink/fan component that is shipped with each processor. There are two sizes of Cyrix heatsink/fan combos. The PR166+ and above has to have a larger, higher capacity heatsink/fan. I was able to determine that I received the Cyrix certified heatsink/fan with my PR166+ because it had Cyrix written in green letters on the top of the fan. Check out a picture of it. The heatsink/fan radiates heat away from the processor and transfers the heat to the ambient air inside the case. Proper case airflow design removes the heat from the case by maintaining an adequate airflow rate.

All processors produce heat that may feel hot to the touch. This is normal for all semiconductor devices.

Q. Does Cyrix provide a heatsink/fan with every 6x86 processor?

A. Well, they used to. According to the official 6x86 FAQ Cyrix is no longer providing a certified heatsink/fan with the 6x86. Specifications are now being supplied to assist the reseller in making the right heatsink/fan purchase instead. Just because Cyrix has stopped including a heatsink/fan with every 6x86 does not mean you do not need one. I don’t recommend using a 6x86 without a heatsink/fan. Eliminating it means that Cyrix/IBM have significantly reduced heat issues with the 6x86L.

Q. My Cyrix supplied heatsink/fan sounds like a jet engine. Is this normal?

A. Yes this is normal and it also is a common complaint. The comparison to a jet engine is of course an exaggeration.

The Cyrix supplied heatsink/fan rotates three times faster than most standard heatsink/fans to help reduce heat. As a result, it makes a loud whining noise and can cause a significant amount of vibration if it is not mounted securely.

The Cyrix heatsink/fan is also a sleeve-bearing fan rather than a ball-bearing fan. Sleeve-bearing fans are more common, inherently noisier, and do not last as long as a result of their cheaper design.

Many people have given high marks to the heatsink/fans made by PC Power & Cooling which can be obtained for a very reasonable $25.00. These heatsink/fans consist of a long-life, ball-bearing mini-fan integrated into die-cast heat sink. Custom features include deep-ribbed air channels and contoured fins for efficient heat transfer, mounting posts for distortion-free fan alignment, and a unique bi-directional fan shroud for maximum air velocity. They are also very thin.

I have heard from others that these heatsink/fans are very quiet and did a good job of reducing heat. The noise has really never been an issue with me, although I do agree that the Cyrix supplied heatsink/fan is louder than most.

Q. My Cyrix 6x86 can operate using both 3.3V and 3.52V. Which voltage setting should I use?

A. If your 6x86 can operate using both 3.3V and 3.52V voltage settings, you have a voltage switching 6x86. Your chip can run properly using either voltage setting. The reason behind voltage switching chips is to accommodate a variety of motherboards. I own a voltage switching 6x86 and I set my voltage setting to 3.3V. I suggest keeping it at the lower voltage setting (3.3V) if your motherboard allows it because it requires less power consumption and will therefore generate less heat than the 3.52V setting.

Voltage switching 6x86s can be identified by 3.3V or 3.52V markings printed on the top of the chip. Check your motherboard documentation to determine what voltage settings your motherboard allows.

Q. Why is everybody talking about overclocking their Cyrix 6x86? Should I do it?

A. I have been hesitant to write about this subject, but there has been to much interest generated not to discuss it. After all, this page is for the readers.

Overclocking is increasing the clock rate of a processor beyond its manufacturers rating for the purpose of increasing system speed without buying a faster, but more expensive processor. Many people are buying the PR166+ instead of the PR200+ to save some cash, but overclocking it to a PR200+ to squeeze out extra performance. Overclocking the PR166+ simply involves bumping up the bus speed from 66MHz to 75MHz.

The problem is that overclocking may or may not work. It depends on the individual chip. All Cyrix chips are tested and rated after they are manufactured. Some PR166+ chips could very well operate as a PR200+, but barely missed a set of performance criteria established by Cyrix to get the PR166+ label.

A raw 6x86 chip is first speed sorted to determine MHz. The CPU has to exceed the speed tested for. What this means is that any chip that surpasses the speed for a PR166+ but falls short of the PR200+ will be marked as a PR166+. You can probably see why a PR166+ can be overclocked so easily. They are indeed the same silicon wafer that has been cut to die and perform at different levels. The difference can be very small. After the speed is determined the chip is branded with speed and company info and then burned-in for 7 hours at temperatures ramping from room temp to 140*C. After burn-in it is tested for the speed it was branded during what is called 'speed verify' to make sure the burn-in process did not change anything.

There are two real risks to overclocking which are primarily caused by heat:

  1. Data loss, wrong calculations, or system crashes due to CPU faults. This can be quite dangerous for people who process a lot of very important data, but there's no hardware damage. You just have to re-boot your system.
  2. Electromigration. Electromigration is a scary thing because this can cause permanent damage to the chip. The combination of heat and electric field cause the chip to break down. However, the probability of this happening is very small because it happens over time.

A good general rule of thumb to avoid overheating problems is to take whatever cooling method is already in place and go one step beyond it. Here are some ways to reduce your CPU's heat:

Often the symptom of a CPU which isn't able to operate while overclocked will become apparent immediately. The system might not boot or if it does it might crash randomly. That has been my experience with overclocked chips that couldn't cut it. For more info, check out the Overclocker's FAQ or the extremely comprehensive Overclocking Guide.

Q. Will using a heatsink compound help reduce processor heat?

A. Yes, you can purchase a heatsink compound from Radio Shack or most electronics stores that you can apply between the CPU and heatsink/fan to help reduce processor heat. The compound helps reduce processor heat by acting as a thermal conductor which increases the amount of heat transferred from the CPU to the heatsink/fan. This helps cool the CPU.

This compound also eliminates any air between the CPU and the heatsink/fan. As a result, it creates a more efficient thermal path than the standard heatsink/fan clip-on method because there is no air gap.

I purchased a silicon heatsink compound at Radio Shack (Cat. No. 276-1372) that only costs a couple of dollars and works very well.

Note, you should apply a paper thin layer to the surface of the core (1" square) of the processor. Avoid applying the compound to the heatsink/fan surface itself. If you use to much its worse than not using any at all.