The majority of the overclocking fun takes place on the page shown below. You can set front-side bus speed, CPU multiplier (this is supported on the Pentium M but not the Celeron M, and the multiplier can only be adjusted down from its original setting) and lock the PCI and AGP busses. Voltage adjustments are available for CPU, DDR and AGP.
It should be noted that BIOS features are implemented not on the CT-479 but on its host motherboard. In addition, supported features vary from motherboard model to motherboard model, so you'll want to research as best you can to ensure that any advanced features you want (such as CPU voltage control) are available in the latest BIOS of the motherboard you plan to use.
For example, Asus sent along a P4C800-E Deluxe motherboard to go with our CT-479 review unit. This is an Intel 875P-based board that certainly doesn't skimp on the features. You can read more about it here. The first P4C800-E BIOS with CT-479 support was missing out on the ability to adjust the voltage of the CPU. The most recent BIOS (1022) took care of that problem, and took care of it well.
Unlike previous Pentium M desktop solutions we've seen, which capped the CPU voltage at the processor's upper range, the P4C800-E BIOS allows the voltage to go up to 1.6V. Considering that the maximum recommended voltage for our test chip (a 2.0GHz Dothan) is 1.34V, Asus has given you plenty of rope with which to hang yourself.
A few brief notes, because things got a little complicated this time around:
Obviously we wanted to see what effect dual-channel memory would have on the Pentium M's performance, so testing against DFI's 855GME-MGF was a must. Since this review also marks a brief return to a socket and chipset of yesteryear, we decided to throw in the hottest chips (both figuratively and literally) ever to run in Socket 478, a trio of 3.4's: the Pentium 4 "Northwood" 3.4GHz, Pentium 4 "Prescott" 3.4E, and the Pentium 4 Extreme Edition 3.4GHz.
We considered testing the Pentium M configurations on a 400MHz front-side bus, but due to limitations of the P4C800-E Deluxe motherboard, the Asus configuration would have been limited to DDR266 speeds. We wanted a single vs. dual-channel test with the same RAM speed on both the DFI and Asus boards. Since a 533MHz front-side bus is the future of the Pentium M, and 533MHz parts are already available, we therefore used the overclocking features of each motherboard to test our Dothan chip at speeds approximately equivalent to a Pentium M 770, which runs at 2.16GHz on a 533MHz front-side bus.
Why "approximately?" Well, the BIOS on the Asus board has some counting difficulties. Specifically, when you tell it to run at 133MHz front-side bus, it actually runs at 135. We tried turning it down to 132MHz, but the DDR333 memory speed isn't available below 133MHz. We also tried turning it up to 134MHz, but that threw the RAM divider off. Therefore, we ran both the Asus and DFI boards with a 135MHz front-side bus and a 180MHz memory speed, which matched them up in terms of both front-side bus and memory clocks.
The Asus board's higher CPU voltage options allowed me to push the Pentium M farther than on the DFI board, and I wound up with a maximum stable speed of 2.57GHz. The chip basically hit a wall here. 2.57GHz required only a slight voltage boost, but even a 10% overvolt wouldn't keep the Dothan stable at 2.7GHz. I wasn't willing to go any higher.