Overclocking The Intel Pentium
Intel's Pentium processor is the most successful CPU ever. Because of that it has to come first here. The nice thing about this CPU is that it is also the most overclockable CPU ever. This can be attributed to Intel's increased quality demands put in place after the floating-point flaw disaster. The new Pentium MMX is just as overclockable as the Pentium Classic, maybe even better. This CPU normally runs at 2.8V. Most motherboards that offer this voltage also offer 2.9 or 2.93V. This is only 0.1 V more than 2.8 V and probably just the right thing for overclock-unwilling Pentium MMX CPUs. My own Pentium MMX 200 runs fine with 2.8 V at 208/83 and 225/75 MHz. For 250/83 I have to increase the voltage to 2.9 V and everything works fine. BTW mine's a 'SL23S'.
Please let me put a short note about the so much feared 'overclock protection' from Intel. So far the only thing Intel has done once was disabling the CPU pin 'BF1', which is responsible for the multiplier settings x2.5 and x3. My survey could reveal, that the affected CPUs are about 50% of the 'SY022' and maybe 10% of the 'SU073', both P133 CPUs. You still can run those P133 at 166 MHz, but only with 83 MHz bus speed.
Now since the message about thousands of remarked or counterfeit Pentium CPUs has eventually reached the US, Intel has to at least make some announcements to this counterfeit and overclock protection again, which they did. However already 2 years back, Intel was claiming to soon ship their chips with a overclock protection, which never took place. I still doubt that Intel will invest any money in producing this feature at all. Before they do that, they should and will have to do something against the remarking opportunity of their chips. Hence I wouldn't worry at all. Intel will probably never avoid that their chips can be clocked higher, but they may push the motherboard industry to produce motherboards that don't offer any overclocking abilities.
If you've read all the paragraphs above, you'll remember the following things:
- Always try to increase the bus speed first if you can.
- Don't increase the multiplier while decreasing the bus speed - you won't gain anything.
- Try higher voltages and don't be afraid of it!
- Avoid the P133 'SY022' and 'SU073' if you can.
- Don't buy a remarked Pentium - there are loads of them around!
The most overclockable Pentium CPUs:
- P150 is the absolute winner - it's most likely nothing else than a P166 in disguise!
- P166 Classic & MMX (and hence the P150) is super for 187.5 @ 2.5 x 75 MHz and in most term runs fine at 200 @ 3 x 66 MHz.
- P133 great for 150 @ 2 x 75 MHz or 166 @ 2 x 83 MHz - forget about higher multiplier settings with that CPU.
- P75 most of them run at least flawlessly at 90 @ 1.5 x 60 MHz, many of them at 100 @ 1.5 x 66 MHz.
- P200 Classic & MMX superb at 208 @ 2.5 x 83 MHz, great at 225 @ 3 x 75 MHz, amazing at 250 @ 83 MHz - the CPU for the real speed freaks!
Where do you want to overclock today?
| Pentium at | 1st choice | 2nd choice | 3rd choice | 4th choice |
|---|---|---|---|---|
| 75 MHz | 112.5 MHz @ 1.5 x 75 MHz | 100 MHz @ 1.5 x 66 MHz | 90 MHz @ 1.5 x 60 MHz | 83 MHz @ 1.5 x 55 MHz |
| 90 MHz | 125 MHz @ 1.5 x 83 MHz | 112.5 MHz @ 1.5 x 75 MHz | 100 MHz @ 1.5 x 66 MHz | Row 1 - Cell 4 |
| 100 MHz | 125 MHz @ 1.5 x 83 MHz | 112.5 MHz @ 1.5 x 75 MHz | Row 2 - Cell 3 | Row 2 - Cell 4 |
| 120 MHz | 125 MHz @ 1.5 x 83 MHz | 133 MHz @ 2 x 66 MHz | 112.5 MHz @ 1.5 x 75 MHz | Row 3 - Cell 4 |
| 133 MHz | 166 MHz @ 2 x 83 MHz | 150 MHz @ 2 x 75 MHz | 166 MHz @ 2.5 x 66 MHz | Row 4 - Cell 4 |
| 150 MHz | 166 MHz @ 2 x 83 MHz | 187.5 MHz @ 2.5 x 75 MHz | 200 MHz @ 3 x 66 MHz | 150 MHz @ 2 x 75 MHz |
| 166 MHz | 208 MHz @ 2.5 x 83 MHz | 166 MHz @ 2 x 83 MHz | 187.5 MHz @ 2.5 x 75 MHz | 200 MHz @ 3 x 66 MHz |
| 166 MHz MMX | 266 MHz @ 3.5 x 75 MHz | 250 MHz @ 3 x 83 MHz | 225 MHz @ 3 x 75 MHz | 208 MHz @ 2.5 x 83 MHz |
| 200 MHz | 250 MHz @ 3 x 83 MHz | 225 MHz @ 3 x 75 MHz | 208 MHz @ 2.5 x 83 MHz | Row 8 - Cell 4 |
| 200 MHz MMX | 290 MHz @ 3.5 x 83 MHz | 266 MHz @ 3.5 x 75 MHz | 250 MHz @ 3 x 83 MHz | 225 MHz @ 3 x 75 MHz |
| 233 MHz MMX | 290 MHz @ 3.5 x 83 MHz | 266 MHz @ 3.5 x 75 MHz | 250 MHz @ 3 x 83 MHz | Row 10 - Cell 4 |
To get a P166 running at 208 MHz is a tough thing and requires high quality hardware - I hope I'll succeed with SDRAM and the R-534, if I ever should receive it.
There is no excuse for running a P150 at 2.5 x 60 MHz as intended - this CPU definitely runs at least at 166 @ 2.5 x 66 MHz or 150 @ 2 x 75 MHz, which is even better!!
