Celeron overclocking.

How I got 850mhz for $65, or "Why I love ABIT." See also Overlocking the 300a. This weekend I'm going to attempt to get the 300a to overclock on an Asus P2L97a board, which will be my new Linux station. Wish me luck.

If you read the previous installment, you'd have seen how I got the 300a up to 450mhz. That was fine and all, until the new games started coming out and my formerly high tech machine was displaying a slide-show. I decided to do some research to see how fast my ancient ABIT BH6 (1.0) would actually go.

When I bought the ABIT motherboard 450mhz was the fastest chip it would allow. Being a slot-1 board, I thought initially I'd need to get the faster slot-1 chip available. That would be the 600mhz P2 or Celeron.

But a little research can go a long way - I discovered a BIOS update for the BH6 that will allow for the new FlipChip P3's (FCPGA). These are much like the older P2's but are slimmer, and do not come in the slot-format anymore. This is good for three reasons. First, it uses a lower voltage, meaning the temperature will be lower. Second, it's thinner and easier to cool. Thirdly, this applies only to slot-1 board owners, you can get a FCPGA-to-slot1 converter for about $15. I bought the one made by ASUS that allows you to set the voltage via jumpers. The end result is this: I can buy up to an 850mhz chip without buying any new hardware, except for the chip and the converter.

The next question is ... which chip to buy? A little more research provided the answer. As we all know, the celeron chips are clock-locked at the multiplier, but you can change the front-side bus (FSB) speed to whatever you like, so long as the chip can handle the additional heat.

Being conservative, I wanted to use a "standard" FSB speed, meaning 100mhz. Therefore I searched for a chip that would easily be converted to the 100FSB speed to reach a legal speed. Here are the base speeds and what they can reach at 100FSB:

"Stock" speeds
8.0 x 66mhz = 533mhz (Celeron 533)
8.5 x 66mhz = 566mhz
9.0 x 66mhz = 600mhz

Overclocked speeds
But at 100mhz here's what we get:
8.0 x 100 = 800mhz
8.5 x 100 = 850mhz
9.0 x 100 = 900mhz

With the BIOS upgrade, the BH6 will reach a maximum of 850mhz with a FSB of 100. Therefore the Celeron 566 was the obvious choice. According to the literature, the 566 is also the most overclocking-friendly chip. The 600 would easily reach 750mhz with a non-standard FSB (83mhz), which would put the other peripherals at risk, since they tend to like the speed they were designed for (usually 66 or 100mhz). A word on this: Changing your FSB changes the speed at which your system memory is accessed by your CPU, and consequently the speed at which your peripherals will talk to your CPU and memory. If you overclock your bus speed you also "overclock" your other devices. They will not actually run any faster, but they will be expected to be in synch with the rest of your system. If you have a flakey sound card, video card, network card, modem, or whatever, they may not appreciate talking to the bus at a speed they are not designed for. A critical component is your RAM - buy RAM that is rated at 100mhz or 133mhz, so you know it will be able to keep up with your system. This is why overclocking past 100mhz is possible but risky. You can take the 566 chip up to 112mhz (= 950mhz) - but I didn't do that because (A) I prefer not to worry about something going haywire, and (B) the difference between 850 and 950 is not really noticable.

So, I got the chip, got the slot converter, and away I went. I tried all of the voltage settings and finally ended up getting it to work at 1.7v core voltage. The P3-850 uses 1.65, so I'm pretty happy with this. A word of warning - the chip would not run stable until I used thermal glue to attach the heatsink directly to the chip. Once I did that I ran the box overnight with the 3d screensaver going, which pegs the CPU at 100%. I've had no problems at all. According to the benchmarks, a 566 running at 850 is the equivalent of a P3-750 or 733. Not bad at all.

There is tons of information on the subject, but these sites were very helpful:

Anandtech's FCPGA overlocking guide. - everything you need to know is here.
My 300a page. - still useful, especially for an extra box.
http://www.anandtech.com - great component reviews.
http://www.sysdoc.pair.com - Tom's hardware guide - essential tech site.
http://www.sharkyextreme.com - complete overclocking guide.