Modified from
http://www6.tomshardware.com/guides/overclocking/index.html
by Wattana Rattanaprom
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:
| 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 | |
| 100 MHz | 125 MHz @ 1.5 x 83 MHz | 112.5 MHz @ 1.5 x 75 MHz | ||
| 120 MHz | 125 MHz @ 1.5 x 83 MHz | 133 MHz @ 2 x 66 MHz | 112.5 MHz @ 1.5 x 75 MHz | |
| 133 MHz | 166 MHz @ 2 x 83 MHz | 150 MHz @ 2 x 75 MHz | 166 MHz @ 2.5 x 66 MHz | |
| 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 | |
| 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 |
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!!
Read Important News for Overclockers!
The Intel Pentium Pro still doesn't seem to be a popular CPU for overclocking. This is really not fair to the powerful PPro since this CPU works just as well as the Pentium for overclocking.
The first letdown seems to be the lack of any available motherboard for this CPU that runs at a 75 or 83 MHz bus speed. Hence you'll have to stick to the good old 50, 60 and 66 MHz settings. For the PPro the same methods are valid as for the Pentium - first try improving your bus speed.
A PPro150 or
a PPro 180 doesn't deserve to run at the puny bus speed of 50 or 60 MHz.
They are screaming to be overclocked to the 66 MHz bus speed and will reward
you with a considerable performance increase and a high reliability.
| Pentium Pro at | 1st choice | 2nd choice |
| 150 MHz | 166 MHz @ 2.5 x 66 MHz | |
| 180 MHz | 233 MHz @ 3.5 x 66 MHz | 200 MHz @ 3 x 66 MHz |
| 200 MHz | 266 MHz @ 4 x 66 MHz | 233 MHz @ 3.5 x 66 MHz |
I admit,
that it will be tough, to get a PPro180 to 233 MHz and a PPro 200 to 266
MHz, but it's worth a try. The second choices however work out in most
of the cases and the PPro 150 runs great at 166 MHz. The problem with the
PPro is the difficulty to adjust things. Here the SoftMenuTM
technology is a let down, because it wouldn't let you choose 233 or 266
MHz. You can't adjust the voltage either, because the motherboards adjusts
it by itself or more by a VRM module. Nevertheless the PPro is a worthy
overclockable CPU!
I have mixed feelings about writing this paragraph. One one hand, I promised you information on this subject ages ago, but on the other hand, much of the information regarding the 6x86 M1 and the upcoming M2 is about to change. Nevertheless, I will refer to the good old, well known 6x86 and it's later stepping versions.
Due to the massive heat production of the older versions (steppings of less than 2.7) and the overly high heat production of even the latest versions, this CPU is not as flexible as the Pentium for overclocking. The first important thing to remember is that you are indeed able to kill your 6x86 with overclocking. I've never heard of an Intel CPU with this problem, not even a 486, but I have heard several stories of fried 6x86 CPUs. Hence I DO NOT recommend you overclock this CPU at all. The only reason I don't refrain from writing about the 6x86 is that I've been promising this information for a long time.
Overclocking the 6x86 is quite a bit more restrictive than overclocking a Pentium. This is mainly due to its heat production but also can be attributed to it's limited multiplier settings of x2 and x3. You can more or less forget about the x3 multiplier because the only scenario where it makes sense to use it is at 3 x 50 Mhz. Due to the pathetically low bus speed, this is completely uninteresting in the way of performance. Hence this only leaves the x2 multiplier.
If you really want to overclock your 6x86, think small! Think in small steps!! It is worth considering just one step up. This means P120+ (100 MHz) to P133+ (110 MHz), P133+ (110 MHz) to P150+ (120 MHz) and P150+ (120 MHz) to P166+ (133 MHz). The step from the P166+ (133 MHz) to P200+ (150 MHz) seems to be too big and has a fairly low success rate with quite a high risk of losing the CPU.
You'll achieve the highest success rate with 2.7 or 3.7 stepping 6x86 CPUs because they run more stable and produce less heat.
Cooling is paramount for the overclocking of a 6x86, so don't even think about overclocking this CPU without a HUGE heat sink or a power peltier.
I hope all this will all change with the release of the split voltage 6x86. This chip will be run at 2.8 V and should result in much less heat production. Maybe the 6x86 will suddenly turn into a really great overclocking CPU
The K5 has been late in arriving, but is proving to be very powerful indeed. The latest performance figures show fairly nice results compared to the Pentium and the pricing of the K5 is just wonderful! 'How about the overclocking then?' I ask, 'after all AMD is the manufacturer of the most overclocked 486 CPUs in history'. My first overclocked CPU was an AMD 486/40 (to 50 MHz) then an AMD 486/100 (to 120 MHz) and everybody knows about the beautiful and cheap AMD 5x86-133, which just runs great at 160 MHz and still is faster than many P100 systems.
In my initial experience, the older PR75, PR90 and PR100 K5 CPUs are not great fellows for overclocking. Most of the time, the system would remain dead after moving up only one step and these versions share the same serious heat problem with the 6x86.
The PR120 and PR133, however, seem to be much better candidates. These two guys run at the same external and internal speed as the PR90 and PR100!! This proves that the chip inside has been improved and altered. Obviously these CPUs don't produce as much heat as the first incarnations, which is one of the first requirements for overclocking. The new PR150 and PR166 (at 120 and 133 MHz) seem to be of the same design.
Unfortunately I haven't got enough information to tell you anything decent about successful overclocking of the K5, but I hope that'll change. My Overclocking Survey has already got quite a lot of K5 entries.