PC Overclocking, Optimization, and Tuning - 2th Edition

Basic Principles of Overclocking Pentium II and Pentium III Processors

Unfortunately, Intel Pentium II and Intel Pentium III processors cannot be overclocked by means of adjusting the multiplier, which establishes the ratio between the clock frequency and FSB frequency. Intel has developed a number of methods intended to prevent overclocking of their processors as much as possible. As a result, in all newer processors the multiplier is locked. By locking the multiplier, Intel protects its processors from re-marking. Besides, Intel also protects its market by preventing inexpensive processors overclocked from competing with faster and more expensive genuine Intel processors.

Beginning with the Pentium MMX-166, Intel processors generally do not allow you to change the clock frequency by adjusting the multiplier, although there may be a chance that you have an Intel CPU manufactured before the company started to lock the multiplier. This, however, is a very rare exception from the general rule.

Thus, Intel Pentium II and Intel Pentium III processors can actually be overclocked only by increasing the bus frequency. So, for instance, a Pentium II 266 (4×66 MHz) can be overclocked to 300 MHz (4×75 MHz) or even to 333 MHz (4×83 MHz). A Pentium III-500 processor (5×100 MHz) can be overclocked to 560 MHz (5×112 MHz). Generally, this can be successfully done without increasing the processor voltage.

Note that as processor manufacturing technology becomes more advanced, manufacturers lower the levels of voltage supplied to the processor in order to reduce power consumption and therefore decrease heat release. It's not uncommon that processors of the same type, characterized by the same clock frequency and bus frequency but manufactured at different times and therefore having different serial numbers, also differ by the voltage they consume. The BIOS of most modern motherboards usually detects the power supply voltage required by the processor correctly and without much trouble. However, in order to maintain stability at faster frequencies, you'll need to supply your CPU with more power. Of course, the required voltage levels will be different for different processors. Also, the methods of tweaking the voltage will differ. This is exactly why different sets of parameters may prove optimal for different motherboards and processors. For example, the voltage used may differ from the recommended values. For some other motherboards, overclocking is simply impossible. Such motherboards automatically determine all modes for the processor, and provide no way of changing them. But in any case, before you begin experimenting, you should provide efficient extra cooling for both the processor and the other components.

Re-marked Intel Pentium II Processors — an Obstacle to Overclocking

Changing the mark on a processor, i. e. re-marking, is an illegal practice. Remarking began almost as soon as the first processors appeared on the market. This practice became common and widespread with 486 and Pentium processors. Essentially, the re-marking procedure itself is simple enough. Using a special machine or even a saw, the re-marker removed a thin layer from the case enclosing the microchip. After polishing the surface, the re-marker placed a fake mark onto it, usually with an overrated clock frequency. Often, other information, such as data on the manufacturer, was forged as well. Distinguishing a re-marked processor from the genuine product is not an easy task. Processors of the same generation are often very similar in technology, and, most often, even the same semiconductor wafers were used to produce them. Re-marked processors usually work just as well as real ones. Because of this, many companies (Intel, for example) developed a number of defense strategies for their processors. This defense also relates to protecting processors from overclocking.

In the relatively new and modern Pentium II processor, additional defense measures are implemented. For example, the multiplier is now locked using a special circuitry that prevents setting the multiplier value to anything other than the value set by the manufacturer. Unfortunately, professional re-markers usually have little trouble removing this multiplier lock. They simply open up the cartridge and remove the bothersome defense circuitry.

There does exist certain software that is able to tell a real Intel Pentium II 300 processor from a fake. This is done by analyzing the cache memory in the processor's cartridge. This is possible because an Intel Pentium II 266 uses a level 2 cache memory without ECC (error correction code), while Intel Pentium II 300 processors are supplied with a cache memory that includes ECC. However, according to some sources, Intel did release some Pentium II processors rated to both 233 and 266 MHz, and both using ECC. These processors were mostly meant for use in servers. It turns out, then, that the test for ECC isn't completely reliable, and doesn't always produce correct results.

The fastest and more advanced high-performance Intel Pentium processors rated to run at 350, 400, and 450 MHz also have a built-in circuitry intended to protect them from overclocking. Basically, this consists of the multiplier lock. There are also additional protective circuits related to the use of certain L2 cache memory chips. This cache memory works well at the manufacturer-specified frequency, but produces persistent errors when the operating frequency is significantly increased. This method, however, is under development, and because of this has not been introduced on a wide scale. As it is, however, it may be a big disappointment to professionals and to overclocking enthusiasts.

You should note that you are least likely to find a re-marked processor among the in-box products. These processors are much harder to re-mark than, for example, OEM versions.

There are other methods of protection, which as of yet are being planned by Intel and other processor manufacturers. For example, the manufacturers are planning to introduce various identification circuits into the processor architecture, similar to the ones used in the Intel Pentium III. There has also been a proposal to fix all of the frequency parameters. Fortunately for overclocking enthusiasts, this is still only a future possibility for the manufacturing firms.

Increasing the Bus Frequency

With the appearance of Intel i440BX chipset, a good number motherboards appeared on the market that were built on its basis. These motherboards were the first to support a standard host bus frequency of 100 MHz. Support for a bus frequency of 100 MHz provides the ability to significantly increase the processor clock frequency, and therefore the overall performance of the system. Some manufacturers widened the range of supported bus frequencies by adding even higher values, such as 133 MHz or even 150 MHz. This is undoubtedly a significant technological advance towards increasing computer performance by means of overclocking.

Many motherboards were released that strictly followed Intel specifications (Intel's own boards for example). Unfortunately, these boards allow setting of the bus frequency to 100 MHz for Intel Pentium II processors only, with the clock frequency no less than 350 MHz. This relates to the fact that Intel Pentium II and Intel Celeron processors assign their own bus frequency. That is, depending on the processor you use, the host bus will function at 66 or 100 MHz.

However, like any other protective measure of this type, automatic setting of the bus frequency can be easily removed.

On the processor chip, there is a special pin responsible for automatically setting the value of the bus frequency. Its number is well known — pin B21.

All you need to do is to disconnect pin B21, which will allow you to work at a bus frequency of 100 MHz with a processor that normally would only support a bus frequency of 66 MHz. Thus, you will be able to overclock the processor and the other subsystems by means of increasing the bus frequency. Disconnecting this particular pin is a relatively simple task, which, however, still demands care and accuracy. There are several methods of accomplishing this task.

First, you could simply cut the pin off, but this certainly can't be considered the best method.

Second, you could put some adhesive tape around the pin. This also isn't the best way to accomplish your goal. Plus, the glue from the adhesive tape will gradually oxidize the pin and may slide into the motherboard plug.

Third, you could try to cover pin B21 with an insulating varnish. This may be, for example, a special colored or colorless varnish, nail polish, or even parquet lacquer. This is probably the most effective method. However, if the temperature gets too high, the lacquer's structure may change. This may result in the isolating properties of the lacquer being lost, or, just as bad, the polymer film may turn into glue. Epoxy lacquer works very well, and you might want to use epoxy resin instead of lacquer altogether.

Having attained a higher bus frequency, you must keep in mind that components like the processor, the video card, etc. need proper and effective cooling. As a rule, you will need to use additional cooling equipment.

If the processor begins to work unstably, and you can't find a way of resolving the problem, you will have to restore contact to pin B21.

For a more in-depth analysis of the temperature conditions within the computer, and estimates on which cooling facilities you might need, the tables below contain data on the power dissipated by Pentium II and Pentium III processors.