A64 Overclocking Guide

[Uber_Gamer]

After doing a bunch of research and looking up articles I've included short intro and then I'll link two REALLY useful articles.

Before delving into the world of A64 it needs to be known that overclocking the A64 is dramatically different from overclocking the P4 and XP due to a different architecture. In previous architectures, a Northbridge existed between the memory bus and the CPU. The rate at which data was transferred between the memory and CPU was known as the FSB. However, the A64’s memory controller is integrated into the chip, and as such, has no Northbridge, nor a FSB. The A64’s have two independent buses. One is one between the memory and the onboard memory controller. The other is a bus that communicates with the other system devices, known as the HyperTransport bus (HTT). As with FSB, the CPU Clock speed is obtained by multiplying the HTT by the CPU clock multiplier. Yet after this, the similarities between the HTT on the A64 and FSB on previous architectures start to diverge. Before, the Memory Speed was synonymous with the FSB and could be manipulated by FSB/memory ratios. In contrast, in the A64, memory speed is derived off of the CPU speed in CPU/memory ratios. (This will be explained better in the two links) This is why it’s rather inaccurate to say that the memory is ever running “synchronously.” The memory is always running asynchronously with respect to the CPU speed, off of which it’s derived. How fast it’s running with respect to the HTT does not matter at all. There is no latency hit in running the memory slower than the HTT. The HTT's effective speed is determined by an LDT multiplier. While the front side bus could’ve been traditionally double or quad-pumped, the HyperTransport’s effective data rate can be anywhere from 1x to 5x it’s speed on the CPU. So, discluding voltages and othet tweaks, essentially 5 things are being configured/manipulated to overclock the system: The CPU Multiplier, the HyperTransport Bus speed, the Memory Speed, the LDT Multiplier, and the CPU to Memory Ratio. Just a note, though it will be explained in the articles, the CPU Memory Ratio is seen in BIOS as a HTT to Memory ratio. This is not exactly true, that ratio is approximated. The HTT frequency is multipled by the designated CPU multiplier to get the CPU speed, then the CPU speed is divided by a designated divider to get the memory speed. When you set the approximated Memory:HTT ratio in BIOS you're actually setting the CPU divider.

Here are the two very useful links:
HERE
ANOTHER HERE