Thinking of building a new system and want to get the
most bang for your buck? You can sometimes get a lot of extra performance by overclocking
your CPU. Although one cannot be certain beforehand that a processor will operate stably
at higher than its rated speed, Intel is currently manufacturing a CPU that is
particularly easy to overclock. This is not likely to last too much longer however.
Between 80% and 90% of the people who buy an Intel Celeron 300-A and use it with the
right motherboard have found that it can be run stably at the speed of 450 MHz. Unlike the
plain Celeron which has no onboard L2 cache, the Celeron-A processor has 128 KB of Level 2
cache on board and it runs at the CPU's full speed, not half speed like the L2 cache
onboard Pentium II processors. But even though the L2 cache onboard the Celeron-A runs
twice as fast as the cache onboard the Pentium II, the Pentium II has four times as much
of it. This usually balances out their performance in real world applications. Tests with
the Ziff Davis Winstone 98 and GL Quake II benchmarks in otherwise identical systems
actually put the Celeron-A 450 ahead of the PII-450 by a few tenths of a percent.
Intel processors have always had a very large built in safety margin when it comes to
their rated speed. Some time ago, in order to prevent unscrupulous resellers from
illegally remarking their processors and palming them off as faster processors, Intel
began locking the multiplier factor on their CPUs. (If you multiply the "Front Side
Bus" frequency used by the system RAM and motherboard chipset by this factor, you get
the true internal frequency of the CPU.) Since this multiplier is no longer user
selectable, the only convenient way to overclock a recently made Intel processor is to run
it with a FSB frequency that is higher than the intended value.
The Celeron 300A was designed to run at 4.5 times the FSB speed of 66 MHz used on older
Pentium II motherboards. (That is, 4.5 X 66 MHz = 300 MHz.) But new motherboards using the
Intel 440BX chipset can provide a FSB of 100 MHz. If we set the Celeron 300A to run at 4.5
times 100 MHz, its internal frequency will be 450 MHz.
About half the time, if you have a BX chipset motherboard and use SDRAM memory that
will run at 100 MHz (that is, either PC-100 compliant SDRAM or else ordinary SDRAM that
will tolerate that speed), you can easily run a Celeron 300-A stably at 450 MHz. The other
half of the time, if you raise the CPU core voltage of the Celeron 300A, it will usually
then run stably at 450 MHz. A higher voltage facilitates overclocking because the larger
voltage difference between the digital HIGH and LOW conditions results in
"cleaner" signals for the CPU and other motherboard devices. However,
higher voltages create more heat and heat is one of the reasons that processors have
trouble running faster than rated. Fortunately, the Celeron 300A seems to run cool
and not generate too much heat. Usually a good heat sink and fan will cool it properly
even when running at a voltage a few tenths higher than the norm.
But it is not always easy to raise the voltage of the processor when using a
motherboard with the BX chipset. This chipset was designed to detect the CPU used and
automatically set the "correct" CPU core voltage. Hence this voltage is usually
not user selectable. (There *is* a way to adjust Vcore voltage, but it involves masking a
pin on the Celeron with tape or nail polish and that can be tricky.)
The Abit BH6 motherboard with its patented Soft Menu system is the one BX motherboard
available which allows the user to easily override the default CPU voltage. Normally, the
CPU clock multiplier and the FSB frequency are set by jumpers on the motherboard.
(Obviously the computer case must be open to change them.) The Abit BH6 motherboard lets
the user change the values of these settings as well as the Vcore voltage from within the
BIOS setup. This is very convenient since changes can be done with the case closed. And it
is fortuitous that this quality motherboard also has five PCI slots and sells for a
reasonable price. It is the perfect motherboard for overclocking Celeron or Pentium II
If the Celeron 300A can be successfully overclocked to 450 MHz so easily, why not get a
Celeron 333A and run it at 500 MHz? The answer is that this is much less of a sure thing.
Perhaps the L2 cache on board the 333A will not run at 500 MHz. Or perhaps heat begins to
become a problem at this higher frequency. The Celeron 300A seems to be the best choice
Intel has announced plans to manufacture their future processors so that they will not
run at faster than rated FSB frequencies. They have not said how they will do this,
nor whether the changes will be made to presently available processor lines. As of now,
the Celeron 300A and the Abit BH6 is the combination of choice for overclockers.
As of 12/9/98, the Abit BH6 motherboard can be bought for as low as $94. An OEM 300A
(with a 30 day warrantee from the dealer) can be had for as little as $83, although you
also need to buy a good quality CPU fan and heat sink. An official Intel Boxed Set 300A
comes with an excellent heat sink and fan, has a 3 year warrantee from Intel, and might
An OEM 450 MHz Pentium II costs upwards of $450 without heat sink and fan. So a Celeron
300A is likely to provide PII-450 performance at one fourth the cost. Source: Price Watch .
helpful sites are:
When searching for a Celeron 300A, look for a dealer description like "Celeron
300A Retail Boxed W/128KB L2 CACHE INCLUDES Heat Sink & Fan 3 Year Warrantee".
Note that Intel's boxed set 3 year warrantee does not cover damage caused by overclocking.
However, I have not heard of a single case where a Celeron 300A has been damaged by
overclocking with a Vcore between 1.95 volts and 2.30 volts and a FSB frequency of 100
If Intel is so concerned about their competition that they choose to put out low cost
chips like the Celeron-A that can provide superior performance when overclocked, why not
take advantage and get great performance at low prices? You may even be able to find a
dealer who will sell you a Celeron 300a paired with an Abit BH6 and test them for
stability at 450 MHz before shipping. This takes all of the gamble out of the project
although it will likely cost you an extra %10 or so.