The processor overclocking dates back to very far away past. However, there were only a few cases when the CPUs were used in non-nominal modes. And only when i486 and Intel Pentium processors appeared, overclocking started spreading very quickly having turned into a ubiquitous thing, because the mainboards designed for these CPUs allowed changing the system bus frequency and the clock multiplier. And the period of Intel Pentium 166 MMX domination should be regarded as the golden era of overclocking. Everything could have kept on going like that if it were not only for the end-users who used CPUs in non-nominal modes but also for some dishonest retailers. So, the most CPU manufacturers started doing their best to combat overclocking. Intel was the first one to suffer from this problem.

And so, when Intel Pentium II began approaching the mass users, Intel decided to lock the clock multiplier of its CPUs. This is how overclockers lost their major instrument of that time. However, there remained one more thing, which could help overclock the processors: increasing the system bus frequency, but the results were not that impressive because the mainboards on the basic chipset of those days, i440LX, didn't support any frequencies other than 66, 75 and 83MHz. Another factor, which hindered fully fledged CPU overclocking, was the architecture of Intel Pentium II. Its L2 cache memory was situated on the processor board and worked at half the processor frequency. In other words, the higher got the processor core frequency, the higher got that of L2 cache and the latter very often refused to work fine in this case. That is why i440BX chipset and mainboards supporting 100MHz FSB didn't improve the situation, because the processors intended for 66MHz FSB didn't work fine at 100MHz bus frequency.

However, on 15 April 1998 the situation with overclocking changed drastically. It was the launching of Intel Celeron processor that changed the overclocker's world. This new CPU didn't have any L2 cache and was designed to support 66MHz FSB. Due to these two factors Celeron 266 easily overclocked to 400MHz by means of increasing the system bus frequency to 100MHz. So, the launching of this new processor initially positioned by Intel as a Low-End solution marked the beginning of "renaissance" for overclockers and at the same time embodied the idea of "good performance for small money".

From then on the absence of external L2 cache in the processor architecture was only to the overclockers' benefit. That is why when in August 1998 Intel returned 128KB L2 cache to its Celeron processors, but this time it was not an external cache but an on-die one, it didn't tell on the overclockability of low-cost CPUs. Despite the locked clock multiplier with the increase of FSB frequency Celeron 300A could be overclocked to 450MHz, and Celeron 333 and 366 - to 500 and 550MHz correspondingly.

Not so long ago, since the end of last October Intel started manufacturing Pentium III CPUs based on a new Coppermine core. Besides a more progressive 0.18 micron technology, one of the major peculiarities of this core was an integrated on-die L2 cache of 256KB size. It meant that finally the mainstream processors also acquired overclocking friendly architecture. Which effect didn't keep everybody waiting for long: the youngest models on the Coppermine core, Pentium III 500E and Pentium III 550E, could also work at the frequencies higher than the nominal ones. So, though Celeron processors on the Coppermine128 core, which followed Pentium III, featured a 128KB L2 cache, it was an integrated one and didn't disappoint overclockers.

So, it turns out that today not only the youngest Intel Pentium III models on Coppermine core can be overclocked by nearly 1.5 times, but also the youngest Intel Celeron processors on Coppermine128 core. The tests we carried out were aimed at comparing these processors with their performance when overclocked and with the performance of the elder models working in nominal conditions.

For our overclocking experiments we selected highly overclockable Intel Pentium III 500E, Intel Pentium III 550 and Intel Celeron 566. When choosing the right piece we came across the fact that almost all Intel Pentium III 500E support 750MHz if the system bus frequency rises from 100 to 150MHz. Many Intel Celeron 566 CPUs stand normally the FSB frequency increase from 66 to 100MHz and work at 850MHz. As for Intel Pentium III 550E, working fine at 150MHz FSB turned out a bit more complicated, though possible. And if you want to make sure that you buy a really overclockable processor, you may contact one of companies selling previously tested CPUs.

For our tests we chose ASUS P3B-F mainboard on i440BX. Of course officially this mainboard doesn't support even a 133MHz FSB, not to mention 150MHz. However, if you manage to make it work in non-nominal mode, it will prove the fastest of all, believe us. The main problem you may face when running your i440BX based board at 150MHz FSB, as well as at 133MHz FSB, lies in a significant increase in AGP frequency. For instance, if the FSB is set to 150MHz, you will get 100MHz AGP, which is 50% higher than the nominal. However, our test graphics card, Creative 3D Blaster Annihilator Pro, turned out very robust and these nearly extreme conditions hardly did any harm to it. Besides, with a synchronous i440BX used at 150MHz the system memory also worked at 150MHz that is why if you make up your mind to repeat our successful experience, please, make sure that you use a high quality PC133 SDRAM. And in conclusion, a couple of words about the chosen mainboard. For our extreme purposes we decided particularly on a not very new ASUS P3B-F because it proved the most stable of all during the CPU overclocking. Unfortunately, even a new ASUS CUBX fails to provide the same stability and reliability as the good old buddy - P3B-F.

Well, the test system was configured as follows:

• CPU: Intel Celeron 566 (at nominal frequencies and overclocked to 850MHz by means of increasing the FSB frequency to 100MHz)
  Intel Pentium III 500E (at nominal frequencies and overclocked to 750MHz by means of increasing the FSB frequency to 150MHz)
  Intel Pentium III 550 (at nominal frequencies and overclocked to 825MHz by means of increasing the FSB frequency to 150MHz), Intel Celeron 566 and Intel Pentium III 500
  Intel Pentium III 600E (100MHz FSB) and Intel Pentium III 600EB (133MHz FSB)
  Intel Pentium III 650 (100MHz FSB)
  Intel Pentium III 667 (133MHz FSB)
  Intel Pentium III 700 (100MHz FSB)
  Intel Pentium III 733 (133MHz FSB)
  Intel Pentium III 750 (100MHz FSB)
  Intel Pentium III 800 (100MHz FSB) and Intel Pentium III 800B (133MHz FSB)
  Intel Pentium III 866 (133MHz FSB)
  Intel Pentium III 933 (133MHz FSB)
  Intel Pentium III 1GHz (133MHz FSB)
• ASUS P3B-F mainboard (on i440BX chipset)
• Slot1-to-Socket370 converter ASUS S370-133
• Creative 3DBlaster Annihilator Pro graphics card
• Creative Sound Blaster Live! sound card
• IBM DJNA 372200 HDD
• 256MB PC133 SDRAM by Micron
• MS Windows98

As usual, we began with the performance in office applications. On the graphs you can see the system bus frequency in brackets. And Pentium III 750 (150), Pentium III 825 (150) and Celeron 850 (100) stand in our tests for overclocked Intel Pentium III 500, Pentium III 550 and Celeron 566.

As you can see, the results are quite curious. Pentium III 500 overclocked to 750MHz nearly catches up with Intel Pentium III 800B working at 133MHz FSB and leaves behind Intel Pentium III 800 with a 100MHz bus. And Intel Pentium III 550 overclocked to 825MHz manages to jump even higher: its performance almost equals that of Intel Pentium III 933. This impressively high performance of the overclocked processors can be explained by the fact that the increase in FSB frequency on i440BX based mainboards leads to the proportional increase in that of the memory. In other words, if you set the FSB to 150MHz, the memory frequency will immediately get equal to 150MHz as well. As for Celeron 566, it shows a bit lower performance, though the increase in its FSB frequency causes a really huge growth: up to 850MHz. According to this benchmark, if overclocked, it performs close to Intel Pentium III 667 with 133MHz FSB and to Intel Pentium III 700 with a 100MHz FSB.

These results are practically the same as in the previous test. No wonder, since both benchmarks, SYSmark and Winstone, use sets of office applications to measure the performance. That is why a Pentium III 500 overclocked to 750MHz performs close to Intel Pentium 800 and Intel Pentium III 550 overclocked to 825MHz proves almost as fast as Intel Pentium III 866. And again let's say a few words about Celeron 566, which got overclocked to 850MHz when the system bus frequency rose to 100MHz. Despite this high frequency, its performance is just a bit higher than that of a 100MHz Intel Pentium III 700 and a 133MHz Intel Pentium III 667.

So, we no longer see the amazing performance of Celeron processors in the epoch of Intel Pentium III built on Katmai core. Though Celeron's L2 cache was four times smaller than that of Pentium III, it worked at the twice as high frequency and featured a considerably lower latency being integrated into the processor core. The results shown by overclocked Celeron processors were often higher than those of the corresponding Pentium III working at the same frequency. Now the things have been changed so that both processors, Intel Pentium III and Celeron, were built on one and the same core and the only difference between them remained the L2 cache size. So the today's Celeron seems to have lost all its advantages compared to Pentium III, which got reflected by the performance: because of the small L2 cache the hits appear less probable and hence our Celeron processor will have to turn to the slow system memory more often.

Really, associative cache memory working algorithm requires splitting L2 cache and system memory into equal number of parts, so that to make each part of the system memory responsible for the corresponding part of the cache memory. In the first place, this should speed up data search within the cache when the CPU addresses a certain field of the system memory. Since Celeron and Intel Pentium III can boast absolutely the same L2 cache construction, L2 cache of Celeron CPU is twice as small and the size of its certain sectors is also twice as small: four lines against eight lines of Pentium III. This is exactly the reason for the data to appear in Celeron L2 cache with smaller probability than usually, because Celeron's cache gets stuffed too quickly than that of Pentium III.

Passing over to gaming tests we have to stress that AGP bus bandwidth is also taken into consideration here together with the calculating capacity and the FSB and memory bus bandwidth. AGP bus bandwidth, along which the data transfer to the graphics subsystem is carried out, contributes to the overall performance. This fact is a perfect explanation of what we see on the diagram. And we see that the major influence on the performance is made by the FSB frequency. Since the processors were tested on i440BX chipset, AGP bus also got overclocked together with the FSB frequency increase. At 133MHz FSB, AGP bus frequency made 89MHz instead of the regular 66MHz, and as soon as the FSB reached 150MHz, AGP bus got 100MHz. Unfortunately, not all the graphics cards can stand this overclocking normally, however, even at 100MHz AGP bus frequency the AGP bandwidth made only 800MB/sec. It means that in case AGP 4x is enabled, which isn't supported by the board on i440BX chipset, the data transfer rate is still higher in the nominal mode.

Moreover, the memory bus bandwidth is also of great importance especially in Quake 3, in High Quality mode, because the graphics card takes the data for rendering directly from there. That is why a 66MHz Celeron is in the very end of all the rest: with this CPU installed into i440BX based mainboard the memory also works only at 66MHz.

As for Quake3 results in Fast mode, there is nothing extraordinary there. However, the overclocked AGP bus has a certain positive effect. That is why the processors overclocked with the help of a 150MHz FSB are somewhat faster than in office benchmarks. For example, an overclocked Intel Pentium III 550 manages to catch up with Pentium III 933 and an overclocked Pentium III 500 easily leaves both 800MHz Intel Pentium III far behind.

Speaking about the performance gain, obtained due to the FSB frequency increase by nearly 1.5 times, it appeared higher for Intel Celeron than for Intel Pentium III. As to this test, the performance of Intel Celeron 566 processor rises by 51%, while that of both Pentium III (500 and 550) CPUs - only by 41%. Although it may seem not that strange from a different viewpoint: just take into consideration the fact that with the FSB running at 66MHz the performance of the processor bus in Celeron based systems is significantly limited. While the shift to 100MHz FSB eliminates this limitation and lets the CPU show everything it is capable of.

Again overclocked Intel Pentium III processors look very attractive. Here we should thank i440BX and our graphics card, which agreed to function properly at the frequency 1.5 times higher than the nominal.

As you can see, in case of lower AGP utilization, the systems using 150MHz FSB show slightly lower results, though they are still pretty high. As for Celeron overclocked to 850MHz, its performance again appears between Intel Pentium III 600 and Intel Pentium III 667 as in all other tests.

The results obtained in Expendable are quite logical and predictable.

In conclusion we would like to draw your attention to the economical side of the matter. The today's cheapest processor is Intel Celeron: only $100. It is about 70-80% lower than the cost of Intel Pentium 500 or 550. That's why if you don't have too much money at your disposal, Celeron will be the right choice for you. Besides, Celeron 566 performs nearly as good as some other processors for $180, which means that overclocking Celeron won't save too much. In this case Intel Pentium III 500 and 550 look much more attractive. You will have to spend $170-180 on one of the pieces. However, these huge (compared to Celeron) investments will easily pay you back during overclocking. The performance of the overclocked Intel Pentium III 500 will turn higher than that of Pentium III for $380. And a 550MHz model is even cooler than Pentium III 866 sold for $575. The benefit is evident.

Conclusions

Intel Pentium III 500 and 550 proved perfect CPUs for overclocking. Increasing the FSB frequency up to 150MHz in the systems built on these processors results into the incredibly high performance gain. The overclocked CPUs perform very close to elder Intel Pentium III models. Unfortunately, not all 550MHz processors can boast such cool overclockability. However, if you really want to find one, you definitely will.

Our good old i440BX also showed its best. The system built on this chipset and working at 150MHz FSB once again proved that this chipset deserves its popularity among overclockers. We only hope that the upcoming i815 will become a suitable successor and will replace it in full.

However, to our great disappointment Intel Celeron on Coppermine128 failed to please us with its high performance even when overclocked. Of course, it is worth the money it costs but it looks as if the low-cost processors would never have the same success as in the times of Mendocino and Katmai.