X-bit labs

CPU Overclocking Guide (page 5)

Category: CPU

by Doors4ever

[ 10/04/2005 | 10:46 PM ]

Adjusting Frequencies of Other Busses

When I said that all the things in a computer system are interconnected, I didn’t mention that the memory frequency is not the only parameter that will increase together with the growing processor bus frequency. Other frequencies, such as those of PCI, Serial ATA, PCI-E or AGP busses will also get higher. It is even good to some extent, as it can also speed up the overall system performance a little bit, however, if these frequencies get a way beyond their nominal values the system may simply refuse to boot at all. Nominal frequency for the PCI bus is 33.3MHz, for the AGP bus – 66.6MHz, for the SATA and PCI Express – 100MHz. almost all contemporary chipsets know to lock these frequencies at their nominal values, however, it would be good to make sure it is really so. To do it you have to find AGP/PCI Clock parameter and make sure it is set to 66/33MHz.

All this is true for Pentium 4 Intel chipsets, for NVIDIA chipsets and the latest SiS chipsets. However, the early Intel chipsets, SiS chipsets and all VIA chipsets do not know to lock the frequencies at their nominal values. In reality it means that if your mainboard is based on VIA K8T800 chipset, for instance, you will not be able to go beyond 225MHz FSB frequency during overclocking. Even if your CPU can do better than that, you will have to stop at this point, because the system will not recognize the hard drives any more, or because the integrated sound on your mainboard stops working. Although, you can still give it a try, and later in this article we will talk about it.

The HyperTransport bus frequency is very important for NVIDIA chipsets for AMD Socket 754/939 platform. By default it is set to 1000MHz or 800MHz, and it would be better to set it to some lower value before you start your overclocking experiments. Sometimes, you may see the actual frequency written in the BIOS Setup, but in most cases you will come across 5x multiplier for 1000MHz frequency and 4x multiplier for 800MHz.

This parameter may be called HyperTransport Frequency , or HT Frequency , or LDT Frequency . You have to find it and reduce the frequency to 400 or 600MHz (2x or 3x multiplier).

So, we reduced the memory frequency and HyperTransport frequency, locked the PCI and AGP bus frequencies at their nominal values. Now we can play around with the CPU overclocking.