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One stepping beyond

I’m going to go out on a limb here and claim I was responsible for the first overclock published in a UK magazine. I’m almost certainly wrong, but I’ll leave it up to you to correct me with an earlier mention. Back in late 1995, I was writing a review of the first Pentium 150 system for PC Pro. It was common knowledge that the 150MHz part was already going to be superseded in a matter of weeks. So I tried switching round a few motherboard jumpers until I got a setting which worked. As if by magic, I’d increased the clock speed by more than 10 per cent. Then I wrote about how fast the system would be when the 166MHz version arrived the following month. The benchmarks weren’t 10 per cent faster, but it was extra speed for free, and it ran just fine at the higher clock. The PC company in question, the original London-based Carrera, sold quite a few systems as a result.

Then I went home and tried to clock my own Pentium 120 to 133. It worked for a while, but wasn’t rock solid. I ended up having to set the system back to 120MHz eventually. I realise I wasn’t the first to try overclocking – a number of my friends were souping up their 486s, although I didn’t know them back then. I even know a guy who clocked his Z80 from 1 to 2 MHz. But the P150 was my first taster, and it clearly had many implications. For a start, I learned that all processors of a given generation and stepping are essentially the same, and the clock rating is defined retrospectively, based on quality control or even just market demand. Over years of experimentation, too, I learned another thing – just how hard it is to damage an Intel processor by running it too high. I managed to use a Pentium III 600 for about six months without realising the CPU fan had failed, for example. It wasn’t rock stable, but it’s still perfectly okay, and sits folding proteins 24 hours a day even now.

"I learned that all processors of a given generation and stepping are essentially the same, and the clock rating is defined retrospectively, based on quality control or even just market demand."

The Pentium 4 has carried on this tradition, and proven itself to be about the best overclocker’s processor yet. If you’re a Pentium 4 owner and you’ve employed refrigeration, you might have forced close to 50 per cent more clock cycles out of your CPU. Even just using air cooling, there’s a good chance you can push a 200MHz FSB to 250MHz or more. Overclocked P4s or their Xeon siblings regularly top benchmarking charts, such as Futuremark’s PCMark 04 Top 20. Incidentally, you’ll notice UK-based Armari either at or near the top of that particular chart. Armari made a name for itself back in 1997 by being the first UK PC manufacturer to employ refrigeration. They overclocked twin 200MHz Pentium Pros to 266MHz. Okay, the system took around 20 minutes to boot, but this was many years before Vapochill or the now defunct Chip-Con started making stock refrigeration systems. Even KryoTech was just a twinkle in the eye.

But the overclocking supremacy of the Pentium 4 is under threat. Intel’s LGA775 processors have so far proved themselves far more reluctant to allow extra performance for free. The primary reason for this is Intel’s infamous clock-locked chipsets, which prevent overclocking past about 10 per cent. My own attempts have proven even more dismal. Using the new 915G-based Shuttle SB81P XPC, I couldn’t get the FSB past 214MHz with either a 3.4GHz Pentium 4 EE or a 3.6GHz Pentium 4e. And that was with Geil PC4400 DDR RAM. In comparison, the 875P-based Shuttle XPC SN75G2 hits a 250MHz FSB with ease.

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James Morris


You can put your conspiracy theories about Intel aside, however. Apparently, the overclock lock is due to the inability with 915 and 925 to tie down the PCI Express and SATA frequencies. According to AnandTech (www.anandtech.com), Asus and Abit have managed to get around this, just as a number of motherboard manufacturers managed to make the 865 chipset readily overclockable. Asus’s P5AD2 Premium can be pushed to 278MHz, using some manipulation of the PCI Express and Southbridge frequencies at boot. There’s also talk of LGA775-socket motherboards using the venerable 875P instead, just as there are now dual Xeon boards with this supposedly single-CPU chipset, such as Asus’s PC-DL Deluxe and Iwill’s DH800.

Intel has never really liked overclocking. Despite the Blue Mountain motherboard and PAT technology in the 875 chipset, the company doesn’t want you to be able to buy a lesser processor instead of a faster one – for quite understandable economic reasons. The problems with overclocking LGA775 systems must have seemed like a godsend, even if they’re not an entirely deliberate attempt to curtail increased frequencies. A few more manufacturers will follow Asus’s and Abit’s lead in finding ways round the PCIe/SATA problems, but it’s likely that most mainstream PCs won’t have much headroom for extra performance.

"All this lends credence to the current mood in the enthusiast community that mobile processors are the way forward. The Athlon XP-M 2500+ has proven itself capable of more than 50 per cent extra clock cycles."

All this lends credence to the current mood in the enthusiast community that mobile processors are the way forward. The Athlon XP-M 2500+ has proven itself capable of more than 50 per cent extra clock cycles. There are standard ATX motherboards available for the Pentium M, too. It’s already giving the Pentium 4 a run for its money in notebooks, which is amazing considering that it operates at only slightly more than half the clock speed. A bit more voltage and serious cooling could make it an overclocking monster.

There will always be ways you can get more out of your hardware, despite deliberate or accidental limitations built into the hardware architecture. But it’s still sad to see brand new, all-singing chipsets like 915 and 925X arrive with overclocking ceilings built-in from the outset. It seems like a step backward. With Intel’s stronghold in end-user sales to people who are unlikely to even consider overclocking, why hobble the hardware for the more adventurous amongst us? Intel’s more likely to lose enthusiast sales than gain them as a result, which is a shame considering how long we’ve been able to reap the pleasures of overclocking the company’s processors.