AMD K8 Overclocking Guide
Date: 2006-04-12 20:17:46
Overclocking exampleOk, let’s look at a sample overclock. I’ve overclocked my Sempron to 2200MHz. The multiplier hasn’t been changed. The FSB has been raised to 275MHz. Logically, you’d thing the HT multiplier is still 4x. However it is a rule that having HT Frequency higher than default brings instability, so I lowered the multiplier to 2x, just to be safe. Lowering the HT multiplier even at 200FSB doesn’t affect performance one bit.
By default, then my memory would be at 275MHz as well. However, I’m using Corsair Value Select PC3200. As some of you may know, it doesn’t overclock well, if at all. So I set a divider. A divider is a ratio between the memory speed and FSB. As we already know, by default the memory to FSB ratio is 1:1. Since my memory can’t handle 275MHz, I had to set an async divider. Here are some dividers:
Those are the most popular dividers in all motherboards. I set the DDR266 divider. My RAM is now at 183MHz since 275MHz x 2/3 = 183MHz. There isn’t any performance hit with my RAM under even default because of the high clock speed. PC3200 has a true frequency of 200 MHz. But it is doubled to 400 MHz due to DDR. The standard is PC3200. This means it has a peak rate of 3200 MB/s and runs at 200 MHz.
If your RAM does overclock, you just have to adjust its timings and voltage in order to reach the FSB on a 1:1 ratio. Tweaking RAM will be an upcoming article. This isn’t the last thing I had to do to end up with my nice overclock. Voltages are critical to maintain stability.
VoltagesThe default voltage for the 90nm CPUs is 1.4V. To maintain an overclock you often need to raise the voltage. They key is to set as low a voltage as possible, yet maintain absolute stability. Raising voltage increases temperature. You must make sure your 90nm CPU doesn’t go far beyond 50°C at maximum load. There may be a need for additional/ aftermarket cooling, but for moderate overclocks, the stock cooling will do. There is usually a temperature monitoring program included with your motherboard. I only raised my voltage 0.04V, so my temperature didn’t go up too much.
The temperature readings are usually off a few degrees compared to a diode attached to the CPU. Most newer motherboards can keep the difference of error within 2-3 degrees Celsius.