Which CPUs Can Be Overclocked?
Talking about the Celeron, you have to distinguish between the three different cores: Covington, Mendocino and Coppermine. Some years ago, Intel needed a low cost processor in order to compete against AMD's K6-2 family. The first chip came with the Covington core (Slot-1, 266 and 300 MHz), which was based on the Pentium II Deschutes. This initial Celeron came without any L2 cache, making it a poor performer and rather unattractive.
Only some months later, Intel released the 2nd generation of Celeron processors, coming with the Mendocino core. This one has 128 kBytes L2 cache on die, running at full CPU clock speed. As most of us should know, this processor is inexpensive and fast. Thanks to the integrated cache memory, it almost reaches the performance of a Pentium II at the same clock speed, even though the PII has four times the cache size (but only running at 1/2 CPU clock). In addition, Celeron's price tag was and still is much more attractive than Intel's high-end processors Pentium II and Pentium III. Two years ago, Intel's yields were already good enough to have most Celeron 300A CPUs running safely at 100 MHz FSB, raising the core clock to some amazing 450 MHz.
The latest Celeron model ist again based on a Pentium core. This time, the core name is 'Coppermine' and the differences between the 'Coppermine-Pentium II' and the 'Coppermine-Celeron' are rather small. Celeron is still officially limited to 66 MHz FSB and it comes with 128 kBytes less L2 cache. The following table will show you the differences between all Celeron cores in more detail.
| CPU core | Covington | Mendocino | Coppermine |
|---|---|---|---|
| Clock speeds | 266, 300 MHz | 300A, 333, 366, 400, 433, 466, 500, 533 MHz | 533A, 566, 600, 633, 667, 700 MHz |
| Slot/Socket | SEP - Slot 1 | PPGA-370 | FCPGA-370 |
| Core voltage | 2.0 V | 2.0 V | 1.5 V - 1.7 Vup to 600 MHz1,65 V - 1,7 V633+ MHz |
| L2 Cache | none | 128 kBytes | 128 kBytes |
| L2 Cache clock | - | Full CPU speed | Full CPU speed |
| System clock speed | 66 MHz | 66 MHz | 66 MHz |
| Multipliers * | 4, 4.5 | 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8 | 8, 8.5, 9, 9.5, 10, 10.5 |
* Just like the Pentium III, all Celeron CPUs are multiplier locked. So far nobody has found a way of changing it.
Thanks to its great overclocking abilities, the Celeron 300A used to be one of the most popular types. Something similar is might happen to the new Celeron 533A and 566, as both CPUs should be able to reach 100 MHz FSB absolutely stable, resulting in 800 or 850 MHz core clock. Merely the processor voltage will have to be increased from 1,65 to 1,7 or 1,75V. You may also try 1.8 Volts, but always keep an eye on the CPU temperature.
Celeron's with Mendocino core can run up to 600 MHz at 2.2 Volts. We tried six different CPUs, but even at 2.3 or 2.4 V there was no way of getting those processors to run faster. One of those processors was an excellent example to show that there is no guarantee for overclocking success. One of our Celeron 400 samples did not even want to run stable at 500 MHz (83 MHz system speed). At the same time a Celeron 433 ran reliably at 600 MHz core speed (92 MHz FSB).
We have to face it. Some Celerons just cannot reach really high clock speeds. I hope you can live with the fact that you have to be a little bit lucky, as there is no way to distinguish a good overclocking processor from a bad one unless you try it out. Some processors can be speeded up extremely well; others will fail at 15% more clock speed.
