 The magazine of the Melbourne PC User Group Over-clocking Celeron CPUs George Skarbek gskarbek@melbpc.org.au |
 |
You may have read in a review, conducting a benchmark on the new 500 MHz Pentium III chips, that one of the comparisons was with a 300 MHz Celeron processor running at 500 MHz. Have you wondered how they were able to run a 300 MHz CPU at 500 MHz? They just over-clocked it, most likely without even having to open the computer case.
Running a CPU (Cental Processing Unit) above its rated speed is called over-clocking. This is a very cheap way of getting a faster computer at zero cost. If you can achieve a 300A MHz Celeron running at 500 MHz then you will have nearly 90% of the Pentium III performance at about 10% of the cost.
Most CPUs are capable of running faster than their specified speed but the 300A MHz Celeron has probably the most potential as it uses the core design of the Pentium II with modifications to the cache. As the major costs are in design of the CPU, Intel has used the Celeron to regain the low cost share of the market. During the production of these CPUs, Intel does not run their fabrication plants to produce a certain speed chip and then produce a batch to run at a higher speed. Because of the variability during the processing stage, they test the final product to see at what speed the units are capable of running. As the market determines what can be sold, very many faster CPUs are sold as the slower CPU.
There are two factors that determine the rated speed of the CPU. These are the system bus speed and the internal clock speed. (The bus is the collection of data paths on the motherboard, similar to a multi-lane highway.) The standard system bus speed is 66 MHz so a 300 MHz Celeron has an internal clock speed of 4.5 giving 66 x 4. 300. With proper cooling, most Celerons can be run well above their rated speeds by increasing the bus speed.
However, to be able to run at the faster bus speed, all your other components, such as memory and video cards, must be capable of running t this higher speed. Errors might result from some older components refusing to run properly at the higher bus speeds. To run reliably at a bus speed of 100 MHz, you must have PC100 SDRAM installed.
Dissipating heat is the number one priority in successfully over-clocking any processor. Heat is generated at the core of the CPU, and the faster you clock your CPU, the more heat will be generated.
In the past I have been against over-clocking as it was difficult to do (altering jumpers on the motherboard) and there was a real chance of frying your CPU. However, if you have a relatively new motherboard that allows you to alter the clock and bus speed via the BIOS and displays the CPU core temperature and allows you to set a limit, which if exceeded automatically slows down the CPU, then it should be possible for you to experiment.
|
|
See Figure 1 for a BIOS where the CPU speed can be set via the keyboard and the core temperature is displayed.
General literature and comments from experienced users suggest that the retail Celerons have adequate heat sinks and cooling. My experience confirms this.
For any user who wishes to experiment, assuming that you have the 300 MHz Celeron, try increasing the bus speed to 83 (to get 375 MHz) and if the computer is stable for one or two days, increase it to 100 (to get 450 MHz). The majority of Celerons should cope with this speed. To achieve 500 MHz you will need the bus speed of 112 and this may be pushing too much in some cases and the computer may become unstable, re-booting or locking up. Overheating may become a problem at this speed in warmer conditions. However, even when running your computer at 450 MHz instead of 300, you will notice quite a significant improvement in performance without having to run any benchmarking software.
With a Celeron the clock multiplier is set to 4.5 and cannot be increased. (Earlier Pentium IIs can have their clock multipliers increased but generally cannot be over-clocked by much.) Therefore, changing the bus speed is the only way of increasing the CPU speed.
Remember to monitor the CPU temperature regularly as you increase the speed. This must done immediately after you shut down. Re-boot, go into BIOS setup and check the temperature. Good ventilation at the back of the computer is essential and a larger heat-sink may be necessary at high clock speed or on very hot days. Prolonged running at a higher speed may shorten the life of the chip. However, the consensus among experts is that you can expect at least 5 years of continuous over-clocked running. By then the 64-bit CPUs running well over 1,000 MHz will probably cost a lot less than the humble Celeron.
Remember that ultimately over-clocking is done at your own risk. A
cooked CPU will not be covered by warranty.
Reprinted from the July 1999 issue of PC Update, the
magazine of Melbourne PC User Group, Australia
