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The Overclocker's FAQ

Number of accesses to this page: 5033 since Wed Sep 13 14:14:59 1995


This page, while informative is still incomplete. If you have any suggestions please let me know.

Email me with your other favorite Overclocking pages and I'll add the links here!

Table of Contents:

What is Overclocking

How is it done?

Processor types

Bus and Processor Speeds

What does it all mean?

The Specifics... How to do it

What about the multiplier settings?


Is heat the only problem?

Data Integrity

The Moral

The Disclaimer

My experiences

Common 486 overclocks

Known not to overclock (usually)

The Pentium World

Pentium Information

Some more words of advice

Any Questions?

Corrections and Additions

Things I'd like to add to this FAQ

About the Author


What is Overclocking

Overclocking means running your computer's CPU at a speed higher than what was intended by the manufacturer. Those who choose to overclock their CPU's do so because they are able to see better throughput out of their overclocked system. There are some considerations that a person needs to think about before overclocking however. For example, an overclocked CPU may have a shorter life span. Additionally, overclocking introduces a higher potential for computational errors; errors which my not be noticed until it is too late. This FAQ is intended to explain some of the details related to overclocking as well as the potential problems involved.

How is it done

How to overclock ones CPU seems to be the single most popular question on and The process is not really very difficult. The problem is that no two motherboards work exactly alike, and so there will be as many different methods for overclocking as there are motherboards manufactured. Before getting into the details it is necessary to understand some of the basics surrounding the topic.

Processor types

Let's start by discussing a 486 processor (these have been around long enough that most people are familiar with how they work). There are various breeds of 486 cpu's. The major designations are SX, SX2, DX, DX2, and DX4. All 486 processors use a 32 bit data bus. The external data bus is how the CPU communicates with the motherboard. On SX and DX chips the speed of this bus is the same speed as the internal workings of the processor. On SX2 and DX2 chips the internal speed of the CPU is twice that of the external data bus. On DX4 CPUs the internal chip speed is three times that of the external bus. The difference between an SX and a DX chip is the fact that DX 486 chips have a math co-processor and an internal cache whereas the SX chips do not. Ok, so if you have a 486DX33 that means the external bus is running at 33mhz. Morover, the internal processing speed of this chip is 33mhz. A 486dx2/66 also has an external speed of 33, but the internal workings of the chip double that speed to attain 66mhz. The "dx2" chips use a technology that takes the external clock speed at which the motherboard is operating at and doubles it. "SX" and "DX" chips which do not have the "2" at the end of the name (as in "DX2") do not support a 2x mode of operation. This should dispell any rumors that one can take a 486dx33 and turn it into a 486dx2/66 like magic. Similarly, the "dx4" chips have clock tripling technology built in (who knows why it's called a "dx4" and not a "dx3"). This means that again, one may not simply turn a 486dx33 into a 486dx100. Bus Speeds and Processor Speeds

Here is a list of the bus and processor speeds of the most common 486 chips.

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Processor Name: Bus (external) Speed: Internal (processor) Speed: 486sx20 20MHz 20MHz 486sx25 25MHz 25MHz

486sx33 486dx33 33MHz 33MHz

486dx40 40MHz 40MHz 486dx50 50MHz 50MHz

486sx2/50 25MHz 50MHz 486dx2/50 25MHz 50MHz

486dx2/66 33MHz 66MHz 486dx2/80 40MHz 80MHz

486dx4/75 25MHz 75MHz 486dx4/100 33MHz 100MHz 486dx4/120 40MHz 120MHz

Pent.Ovrdrive63 25MHz 63MHz Pent.Ovrdrive83 33MHz 83MHz

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So what does all this mean?

Well, the fact is that on many motherboards the bus clock speed of the motherboard may be set using jumpers or dip switches. I suppose one day someone asked, "What will happen if I set the bus speed of my motherboard to 40MHz despite the fact that I'm using a 486dx33 chip?" This is one of the types of overclocking; setting the bus speed faster than it really ought to be in relation to the intended speed of the CPU. What improvements will I see?

By setting a 486dx33 to a 40MHz bus speed you will find that the internal processing speed of the processor directly follows this modification. The chip will try to operate at 40MHz. By speeding up the bus speed on a DX2 chip the internal workings of the chip will still try to double the external bus speed. That means that a 486dx2/66 operating on a motherboard whose bus speed is set to 40MHz will try to operate at 80MHz. A 486dx4/100 will try to operate at 120MHz if the bus speed is increased to 40MHz. What else can be done?

Some motherboards also allow you to select whether the processor runs internally at 1x, 2x, 2.5x, 3x, etc. the external bus speed. Additionally, the BIOS of many systems allows you to modify the number of DRAM wait states, the cache type and wait states, the ISA bus speed, etc. All of these tinkerings may prove to be of some benefit to overclockers. Ok, let's get specific... How do I do it?

Again every motherboard is different, but here are some general instructions that may help you along.


First, if your motherboard allows you to select the bus speed via a jumper you're in luck. If not, you might find yourself needing to pull out the soldering iron. Those motherboards that do not provide for different bus speeds use a crystal to generate the clock speed. You will have to locate the crystal, desolder it, find yourself a faster crystal, and put it in the old ones place. My suggestion is that if this turns out to be necessary you ought to consider selling your motherboard and buying a used one that does allow for bus clock speed selection. For those of you who may select the bus speed via a jumper here's how its done: Locate the jumper(s) that control(s) the motherboard's clock speed. Figure out how your motherboard is currently set (in fact, you should write it down in case you have to go back again). Then, carefully remove the jumper and replace it in the proper position to set your motherboard to its next faster speed. Here are common speeds: 20, 25, 33, 40, 50MHz. If you are set to 25, try the 33 setting. If you're set to 33, try the 40 setting, etc. Next, verify that there are no other jumpers that need to be modified. Possible necessary changes will include: Jumpering the VLB so that a wait state is added to the bus, jumpering the motherboard so that it still thinks you're using the same type of CPU, jumpering VLB cards so that they know they are working at a faster rate (many overclocking attempt failures are due to VLB cards' inability to operate at a faster speed). Look for any other jumpers that might need to be reset. A motherboard manual for your board is the best tool. I can't answer questions regarding particular motherboards. Now, plug back in, hold your breath, and turn on the system (REMEMBER, YOU OVERCLOCK AT YOUR OWN RISK). See if it will boot. It might not! Before giving up, enter your BIOS's Advanced Setup or Chipset Setup. From within the BIOS's setup work on adding wait states to the DRAM access, choose a slower memory setting (these settings are usually relative to CPU speed), add wait states to the cache system, make sure that your ISA bus is set to run at right around 8MHz (usually this is set by choosing to run the ISA bus at a fraction of the motherboard's bus speed). Now try booting again. It might work. If you find that after slowing everything down in the BIOS's settings you still can't boot or if software continues to crash you might have to go back to normal clock speed... sorry.

What about the multiplier settings?

Now here's where it can get interesting. Some people have found that some dx4 processors also will function in a 2x mode rather than the 3x mode. Take, for example, the 486dx4/100. It's bus speed is 33MHz and the internal speed is around 100MHz. But if you set the motherboard (via jumpers usually) to a 2x mode, and then jumper it for 50MHz externally you will might find that you're able to get the system to work as a 486dx2/100. The advantage here is that the VLB and main motherboard bus is now running at 50MHz rather than 33MHz. This will offer dramatic improvements in video performance (if you have a VLB video card that still works at 50MHz) as well as improved performance of the memory subsystem (assuming your memory subsystem is able to handle this faster speed). There are even reports of some dx4 chips supporting a 2.5x mode. This means that you could set the motherboard to 40MHz, and run the processor at 100MHz, or if REALLY lucky you might be able to get 50MHz external and 125MHz internal processing speed (I've never heard of this working though).

The ability for your system to operate when clocked with strange multiplier combinations depends on many things, but the most important is that the chip you are using must support that multiplier. You can't simply take a 486dx33 and clock it as a 486dx2/66. It just doesn't support a 2x mode.


Higher processor speeds mean higher operating temperatures. These temperatures can KILL your CPU much more quickly than the standard temperature. For this reason it is essential that you use a heatsink on any overclocked system. A good general rule of thumb is to take whatever cooling method is already in place, and go one step beyond. If you chip is bare (no cooling) add a heat sink. If it already has a heat sink add a fan. If it has a fan already, add a Peltzier cooler (like an air conditioner). On my system I have a heat sink on the processor, and an old power supply fan (removed from the supply) pointing right at the CPU. My overclocked CPU now runs cooler than it did before I started messing with it.

Is heat the only problem?

No. Heat is one of the problems. Another is "electromigration." This term refers to a process that occurs over time, where the circuit paths inside of the processor slowly erode. Higher speeds can mean faster erosion. The end result will be microscopic short circuits within the processor. How long it takes for this to occur is difficult to say, and a topic often debated. My opinion is that the amount of time it takes to ruin a normal chip in this manner is going to be longer than the length of time you would want to own the chip anyway. Prices of chips are always falling, and that overclocked dx2/66 isn't going to be very expensive to replace in today's market.

Another potential problem is that your memory subsystem might not be able to handle faster speeds. Maybe your SIMMs are too slow. Maybe your cache is too slow. Maybe a defect in one of the SIMMs doesn't turn up at lower speeds, but does at the higher speed.

Many VLB cards weren't designed to operate faster than 33MHz. If that's the case you will have trouble overclocking.

Data Integrity

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 before too long. While this is unfortunate, the worst potential problem could be the symptoms that might not turn up at first. There is a possibility that an overclocked CPU will only malfunction in a particular situation, and that situation might only happen when you click the "calculate" button on an important spreadsheet. You might not ever notice the malfunction, but what if it has caused an incorrect calculation somewhere? Or what if the malfunction manifests itself by slowly corrupting your hard drive? It may take weeks or years to see the results of a malfunction, and an overclocked chip is more prone to such malfunctions than one operating within specs.

The moral

Back up your hard drive before overclocking. Keep a watchful eye over your system at first. Put it through all kinds of benchmarks and tests. Verify the accuracy of data. Run "defrag" a bunch of times... in short, put the system through the wringer to insure that you're getting a stable system after overclocking.


It should be understood that overclocking means running your system faster than it is supposed to go. Just because it can be done doesn't mean that it's safe. Any time you open your computer you expose it to ill effects. Always backup everything first.

Always be prepared for the worst case. Though I have never heard of someone frying a CPU immediately after overclocking it, that doesn't mean that the potential isn't there. You could even damage your system just by working inside it (static electricity, etc.). I can accept no responsibility for damage caused by tinkering with your system in any way. You overclock at your own risk just as I have overclocked at my own risk. I hope that your experience with overclocking is as successful as mine, but there are no guarantees.

My experience

In my experience I have yet to see a system ruined immediately by overclocking. If you're unable to get an overclocked system to boot properly or run with any stability you should go back to the original speed before any kind of real damage (data loss or hardware damage) can occur. If you are able to get it to overclock successfully then it should be watched carefully at first for signs of malfunction. Generally those who find that their system overclocks easily have few troubles. I have never had a CPU go bad on me. I have never run into a situation where overclocking has caused data loss or hardware damage. Just be aware of the potential for such.

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Common 486 overclocks

Chip Overclocked setting i486dx33 40MHz i486sx33 40MHz 486dx40 50MHz (Note, it is hard to find VLB cards that function at this speed - The AMD chip works the best here). i486dx2/50 66MHz (33MHz external) i486dx2/66 80MHz (40MHz external - Works for me, but some report problems.) AMD486dx2/80 100MHz (50MHz external - Usually the 3.3v version of this chip works well when overclocked. There are some reports of it even functioning at up to 120MHz. This must involve playing with the multiplier.

I have been told that early models of the AMD dx2/80 had a 3x mode that could sometimes be coaxed to work in conjunction with a 40mhz bus speed. This is how 120MHz can be achieved. Apparently, later versions of the dx2/80 do not support the 3x mode and thus are entirely unable to run at 120MHz. i486dx4/75 100MHz (33MHz external) i486dx4/100 100MHz (50MHz external, chip set to 2x mode rather than 3x) AMD486dx2/66 80MHZ (40MHz external) AMD486dx4/100 120MHz (40MHz external)

Known not to overclock (usually):

83MHz Intel Pentium Overdrive -Don't overclock this one. There have been reports of actual processor damage resulting from overclocking the POD83. In any case, there have been no reports to me of overclocking working for this chip. 63MHz Intel Pentium Overdrive -I haven't heard any success stories with overclocking of this chip. Given that the 83mhz version doesn't react well to overclocking I can't recommend trying it with this one either. AMD486dx4/120 AMD486dx2/80 (The 5.0v version doesn't overclock well, but the 3.3v one manufactured after February seems to overclock well in many situations.)

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The Pentium World

Pentium chips seem to lend themselves well to overclocking in many instances. Indeed the Pentium 75 has been successfully overclocked to 90 and 100MHz by many people. There are rumors floating around that Pentium 75's are manufactured on the same line as the 90's and 100's, and that there aren't really any process differences. However, the 90's and 100's have been tested at those speeds, the 75's have only been tested (and guaranteed) to operate at 75MHz.

The late breaking news now seems to be that Intel has begun manufacturing the Pentium chips in a way that eliminates the possibility for overclocking. Apparently those chips manufactured with a "black" plate on the back lend themselves well to overclocking, while the ones with a "gold" plate on the back don't seem to work in most cases when overclocked. Other reports are that the chips marked, "Malay" on the bottom can be overclocked, while the ones marked, "Phillipeans" on the bottom have been manufactured such that overclocking isn't possible.

It should also be noted that the Pentium Overdrive chips, which are made to fit the ZIF sockets of 486 style motherboards are known not to work when overclocked. I have even seen one story of a chip failing to function properly even once set back to the regular speed. Don't overclock these chips (POD83, POD63).

The PCI bus found on many Pentium systems will operate in a 25MHz mode (as with Pentium 75's), a 30MHz mode (for Pentium 90's) and a 33MHz mode (for Pentium 100's). Usually you may use jumpers or dip switches to change the bus frequency and the multiplier for these systems. I haven't heard yet if anyone has been able to successfully overclock a Pentium by changing the multiplier.

The memory bus on Pentium systems operates at either 50, 60 or 66MHz. This is twice the speed of the PCI bus. When you overclock a pentium it becomes even more critical that your memory subsystem be of the quality necessary to handle these higher speeds. Also, you are going to have to do quite a bit of fiddling with the BIOS settings to get everything to run with stability.

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Pentium Information:

Please note: My "Chip Mode" column states the multiplier in terms of PCI bus speed. Some motherboards state the multiplier in this fassion while others state the multiplier in terms of Memory Bus Speed. You will have to determine which method your motherboard uses before you attempt to play with multiplier settings. The multiplier stated in terms of memory bus speed is indicated in parenthesis.

Chip Name PCI Speed Memory Speed Chip Mode

Pentium 60 30MHz 60MHz 2x (1x) Pentium 66 33MHz 66MHz 2x (1x)

Pentium 75 25MHz 50MHz 3x (1.5x) Pentium 90 30MHz 60MHz 3x (1.5x) Pentium 100 33MHz 66MHz 3x (1.5x)

Pentium 120 30MHz 60MHz 4x (2x) Pentium 133 33MHz 66MHz 4x (2x)

Pentium 150 30MHz 60MHz 5x (2.5x) Pentium 166 33MHz 66MHz 5x (2.5x)

The future???? --- Speculations... Pentium 180 30MHz 60Mhz 6x (3x) Pentium 198 33MHz 66MHz 6x (3x) (I'm going to guess that if such a chip comes out it's not going to be called P198... It'll be called a Pentium 200.)

-=- [PREFORMATTED] =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- The general consensus seems to be that overclocking a Pentium to a higher speed within its multiplier mode works, however overclocking via a higher multiplier is not usually successful. Bare in mind that it is crucial to keep these chips cool! Good fans, heatsinks, and Peltzier coolers are not just recommended, they are a must.

Some words of advice

Heat sinks should be applied using a special heat sink glue that transfers heat properly. Simply insuring a tight fit isn't enough. Fans with built in heat sinks should also be carefully applied using proper heatsink compounds. Personally I don't like the heat sink / fan combos. What happens if your heat sink / fan that is glued on burns out (fans do go bad)?

Also, you should check your cooling fan from time to time. They do burn out leaving your processor unprotected. Good airflow next to the CPU is important, but so is good airflow through and out of your computer's case. The whole system should be kept cool, and the fan that cools your processor isn't going to be able to exhaust the heat to outside of your case... your power supply fan does this to some extent, but some people have found benefit in adding a second fan sucking air out of the case. Secondary fans should be installed in such a way that they're not working against the power supply's fan. Morover, case vents should be kept free of obstructions, and should be placed in locations within the case that encourage good air flow around *all* components. I don't recommend those "fan cards" that plug into an ISA slot in your computer. They only move air around within the case. Also, they usually aren't very smooth running...I'm not sure that I like the idea of causing a continual vibration on one of the ISA slots. It seems like that would cause premature wear on the motherboard.


Post them to or Here are some suggestions: If you're going to ask how to overclock your system be sure to have read up first in your manual. If you don't have access to a manual that discusses bus speeds and jumper settings then ask your question on Usenet, but make sure to be very specific. You will have to list your motherboard brand and model number if you expect anyone to be able to give a good response.

Questions like "I overclocked my system, why doesn't it work?" don't usually get answered. Why? Because there are no details listed, and overclocking simply doesn't work in 100% of the cases. It seems that in the chip related newsgroups people are pretty much sick and tired of seeing this type of overclocking question posted.

I can not respond to email requests for overclocking help! It just takes up too much of my time and there are others out there willing and able to help. I do read the above mentioned Usenet groups, and when I know an answer I will respond. But the fact is that 99.9% of the questions that people seem to send me are so motherboard specific that there is no way I could possibly know the answer. Ask Usenet!

Corrections and Additions

I would like to hear if you have any corrections or additions for me to include in this FAQ. Don't send me unanswered questions. What I mean is that you can't simply send me a question like "Do the new P6's overclock?" I don't know! If I did I would have put it in this FAQ. If you sent me an addition like, "P6's do overclock, and here's how it all works..." I will put it in the FAQ. I can not answer individual questions regarding overclocking. Don't ask me, ask the collective body of Usenet. If I see a post there and know the answer I might respond, but if I get emailed by hundreds of people who need help overclocking I'm going to route the email to /dev/null.

Please feel free to contribute to this FAQ though. I don't gain anything by this FAQ, so I can't pay for contributing text, but the collective internet community does appreciate your intelligent input. To send me updates and comments you may email me at In the subject line include "overclocking faq" (anywhere in the text of the subject line, and case insensitive).

Possible additions:

I would like to add a section to this faq discussing actual experiences with actual chips and motherboards. Both good and bad experiences are welcomed. The format will be like this:

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Motherboard Chip New Speed Adjustments Requ'd. Success

Genoa Turbo- 486dx2/66 80MHz Jumper bus to 40MHz Yes express VL-3 BIOS settings

Intel Triton I Pentium90 100MHz Jumper bus to 33MHz Yes Change BIOS settings

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I also will be reorganizing the FAQ from time to time as I figure out what works and what doesn't. If you find this FAQ useful spread the word. I wrote it out of response to the constant drone of newbies asking the same questions over and over again on Usenet. If someone asks a question that you know is answered here, point him or her to this FAQ, and do so publicly (on Usenet) so that other readers will know where to turn as well. Let's all try to preserve the bandwidth on Usenet groups for the discussion of topics not covered by online FAQ's. ---------------------------------------------------------------------------

[*]About the Author

This FAQ was written by David Oswald. Email me with answers... not questions. Ask your questions on Usenet. [*] Please send comments to me, and send overclocking related questions to Usenet. This means you! If I continue to get dozens of questions each day that should be sent to Usenet I'll have to pull the FAQ. [*]Visit David Oswald's Home Page.

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