Choosing the right CPU for overclocking

Examining bus speeds

As you probably know, the processor clock speed is tied to two factors: the system bus speed and clock multiplier. Since Intel locks the clock multiplier on all of their processors the only way to overclock the CPU is to adjust the system bus speed.

In the case of the 600E, the clock multiplier is locked at 6.0x, while the system bus is operating at 100MHz. (6.0x100) For the 600EB, the clock multiplier is set at 4.5x while the bus is running at 133MHz. (4.5x133) With the lower clock multiplier present on the 600EB, the bus speed must be raised to a higher level than the 600E to achieve the same clock speed. This makes the 600E a better solution for overclocking than the 600EB.

As a quick example, to overclock a 600MHz Coppermine to 800MHz, the 600E only requires a bus speed of 133MHz. In contrast, the 600EB requires a bus speed of 177MHz to reach 800MHz!

Some motherboards don't even support bus speeds that high; it would be even more difficult to find components that operate at such a high system bus. Keep this in mind when looking for a new CPU you'd like to overclock.

Unfortunately, other consumers are aware of this as well. With the already limited supply of certain Coppermine CPUs the problem is exaggerated even further.

Identifying your CPU

Believe it or not, you can get an early indication of just how well your CPU might overclock with a quick physical inspection of the processor. Back in the Katmai days, determining the speed of your L2 cache and the age of your CPU was important. Now that the cache is integrated onto the processor die, L2 cache chips are no longer a variable in the overclocking equation. So how do you figure out the age of your processor?

On the top edge of every S.E.C.C. 2 processor is the information you'll need to learn every intricate detail about your CPU. We've provided this picture of our 600E:

The top of our P3 600E

Here's a guide to what all the numbers mean: speed/cache/bus/voltage UL Identifier
FPO-serial# Country of Origin
copyright S-Spec#

Based on this information, we have a 600E with 256K L2 cache designed to operate on a 100MHz bus at 1.65V. The FPO number tells you the year and week of manufacture followed by the serial number. In our case, the "9" denotes our chip was made in Malaysia while the second digit - "0" indicates it was manufactured in 2000. The third and fourth digits "10" denotes it was manufactured the 10th week of 2000.

The S-Spec tells if you the processor is OEM or retail, as well as the stepping of your CPU. You can look up the stepping of your CPU on the Pentium III processor quick reference guide located on the Intel developer website.

Here's what our 600E looked like:

Pentium III 600E