Command Per Clock Guide

Written by John Chen    Friday, 23 July 2004 00:00
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Overclocking is the most addicting hobby I've ever encountered. Video games are another, but not as much. The reason why an ever-increasing amount of people are becoming addicted and going insane with overclocking is that there is no end. You can't reach the end. Someone will always find new tweaks or ways to increase system performance. Someone will always find a way to cool the CPU better. Someone will always find a way to modify that motherboard or video card. Like the universe, overclocking is infinite.

Overclocking starts off with making the right purchase. If you buy cheap or generic products, you'll usually end up tossing it to get something better. To save you all that trouble, I encourage you to just splurge and purchase the best item available. You'll end up doing it anyway. After the purchase is done, and you've spent your afternoon building and cleaning up your system internals, it's time to boot up. You go through your normal procedures of installing windows and your daily programs. Once all this is completed, the fun starts. It's time to reboot again and go into the BIOS.

If you have a good overclocking motherboard, you'll find a plethora of tweaking options. One of the most important options would be the advanced chipset section. This is where you do all your memory tweaks and timings. This is where you'll also find the CPC option for nForce2 chipsets.

Command Per Clock:

Back in the days of the KT266A chipset, I remember being able to go through the usual memory timing adjustments, along with one extra option--command timing. The choices were either 1T or 2T. As chipsets developed, I noticed that this option gradually disappeared. To my surprise, this latency still exists. It's in that nForce2 motherboard you have right now.

This command timing has a new name, labeled as Command Per Clock (CPC). Basically, with it ON, it'll default to 1T. With CPC OFF, the latency is set to 2T. Many AMD users have debated over the issue of whether to keep it ON or OFF. Naturally, enthusiasts would want it set to ON. Systems benefit more from having lower timings. However, the downside to keeping CPC on at is that it hinders overclocking, especially with 512MB double sided memory modules. Why, you ask? The Northbridge controller has issues with reading the memory ranks correctly.

When you have 2x256MB modules, the system will read each as 2 ranks. With 2 sticks in the DIMM slots, it will be read as 4 ranks. When you have 2x512MB modules, the system will read each as 4 ranks (due to the double sided memory). With 2 sticks installed, it will be read as 8 ranks. This is where the Northbridge errors. In order to still function correctly with 2x512MB modules, CPC has to be turned off so the command latency is 2T.