Overclocking 286, 386, and 486 Processors

Computers based on 286 processors are now obsolete. Of course, you can enhance their performance using optimal settings; you can also overclock the processor. But no matter what you do, their data processing frequency will be tens of times as slow as even computers with a 486 processor. However, you might want to use these computers as experimental ground, and increase their performance as a type of training. Besides, these computers can continue to be used as simple word processors.

Computers based on i80286 processors can hardly be upgraded. This is basically because you would need to replace almost every component. This means the monitor, the ISA video adapter — generally CGA or EGA standard, the motherboard, the processor, the hard drive — whose capacity is, by today's standards, inadequate and doesn't usually exceed 80 MB, and the slow RAM with an outdated form factor. The rest of the computer is no better. You'll even have a hard time finding a use for the keyboard that has an 8088/80286 switch.

You can increase the performance of a computer with a 286 processor significantly by increasing the clock frequency. However, using the TURBO mode, which automatically increases the computer operating speed by raising the clock frequency, is pretty much the same as overclocking.

Generally, raising the clock frequency of these processors doesn't present a huge problem. This is because for the majority of the systems two quartz resonators are used: one is related to the timer, the other establishes the clock frequency of the processor. Replacing the second one allows you to increase the operating speed. For example, in a system where the processor clock frequency equals 12 MHz, the quartz resonator is usually set to a frequency of 25 or 30 MHz. Replacing it with a quartz resonator of 33 or 66 MHz allows you to increase the operating seed by up to 16 MHz. Further increase of the processor clock frequency is done in a similar manner.

Overclocking computers with 386 processors, as was the case with the 286 models, more often than not, is not a task with a worthy goal. Instead, it's preferable to upgrade such computers, by replacing the motherboard with, for instance, one with a 486 or even a Pentium processor. Considering the current prices, this doesn't really cost much. There may be certain situations, however, that for whatever reason, such an upgrade is not advisable (even if it is possible). Excluding a computer for which a user has developed a personal affection, examples of these may be, for example, computers with a Slim or UltraSlim case. There are also computers with an exotic type of construct, such as booksize. There are more than a few of these types of computers, and finding a suitable motherboard for them is not an easy task. In such cases, your best bet is to look for some other way of increasing the computer performance. In certain cases, this might just be overclocking.

The particular features of the 386 processor and its motherboard did not well anticipate the next generation of processors. However, these processors were released with the intention of their being able to work at different clock frequencies, for example, at 25, 33, and 40 MHz. In order to keep costs down, motherboards often permitted using processors of various clock frequencies. This is the reason that there have been cases where a motherboard that allows a relatively high clock frequency has adapted to a processor with a lower frequency. In a case like this you can try to raise the performance by running in a mode with a higher clock frequency. This is usually done by adjusting the jumpers and switches that determine the clock frequency of the processor. More rarely, this can be done using BIOS Setup settings. Sometimes, you can raise the clock frequency by replacing the elements of the timing circuit, for example by replacing the quartz resonator or changing the divider.

Usually, motherboards intended for i80386 processors provide no voltage tweaking options.

Information on the capabilities of the motherboard and its modes can be found in the technical literature that comes along with the computer. Often, the necessary explanations of the purpose of the jumpers are shown directly on the board. You can also try to find necessary information on the Internet.

In case it comes down to it, the temperature conditions of the processor may be improved by installing a heatsink with special thermal grease.

The architecture of the motherboards intended for 486 processors is both more complete and more diverse. The clock frequencies of the buses — the processors' internal frequencies — are 25, 44, 40, and 50 MHz. They use processors from Intel, AMD, Cyrix, TI, and IBM. These processors may be of the SX or DX type, and may be able to have their external frequency increased by 2–4 times. Changing the multiplier is usually not provided for in the standard capabilities of the motherboard. The factor is generally a parameter of the internal architecture of the processor.

For motherboards with 486 processors whose case construction is not suited to replacing the processor, the same problems and the same recommendations as given for the 386 processor apply.

The architecture of the majority of motherboards intended for use with 486 processors uses special sockets, which allow you to easily replace the processor on the motherboard. This design raises the level of unification of the motherboard and allows you to reduce its nomenclature for every manufacturer. As a result, many motherboards were created for a wide range of processors with different operating frequencies. It is critical that BIOS recognize them (actually, this is the most important aspect). Information on this is contained in the motherboard manual. There should also be a list there of the possible clock frequencies and voltages for the processor, and instructions on setting these values.

Overclocking motherboards intended for use with a wide spectrum of 486 processors comes down to the procedure of setting them to a higher frequency than was originally intended. For example, for 486SX/25 and 486SX2/50 processors, an external frequency of 33 or 40 MHz is set; for 486SX/33, 486DX/33, 486SX2/66, and 486DX2/66 processors — 40 or even 50 MHz; for 486DX4/75 — 33 MHz, and for 486DX4/100 — 40 MHz. Really good results can be achieved with an AMD processor, the 486DX4/133, which can be overclocked to a bus frequency of 40 MHz. In this mode the 486DX4/133 works at a clock frequency of 160 MHz. As such, for certain tasks the processor performance is equal to that of an Intel Pentium-100 processor.

Overclocked modes demand proper cooling of the processor. You must remember that for 486 processors it is necessary to set them to the voltage for which they were intended. This is why the voltage setting of 486 processors does not depend on the mode and allows you the choice of one of two values, 5 or 3 V.