Introduction
Over the past couple of years processor speeds have reached incredible heights. It doesn't seem so long ago that we all saw the internet buzzing about the golden 1 GHz CPU barrier being broken, even the 2 GHz barrier has since been broken and at the end of the year we should be looking at 3 Ghz. This is great for the consumer, faster processors mean faster frame rates for games etc, well that's what the processor manufacturers tell you. During all these great leaps of CPU MHz, there's one thing that hasn't been leaping in proportion - the bus speeds, mainly the bus that feeds the CPU and the system memory. This is leading to a huge bottleneck forming between the CPU and the memory subsystem, causing the overall performance gains from sheer CPU MHz alone to be falling off dramatically.
This system bottleneck is particularly more prominent on the AMD Athlon XP platform. The current Athlon XP chip's only have 256 KB of cache to act as a buffer for the huge difference in CPU speed and memory speed, this is opposed to the 512 KB cache of Intel CPU's. The buffer is smaller and the speed of the memory and front side bus is more limiting than ever.
For the over clocker and the enthusiast there is a solution to this problem: Buy faster memory and push your Front Side Bus up as much as you can. Officially, for DDR, the fastest memory a non-overclocked system can take is PC2700 which is equal to a 333 MHz DDR bus. On present platforms the current official front side bus is 133 MHz, and more modern motherboards allow you to run RAM asynchronously at 166 MHz. But even a 166 Mhz memory bus speed is not enough to reduce the effects of this system bottleneck.
Memory manufacturer's have answered the needs of the enthusiast PC market and have decided to release PC3200 memory, which officially has no real specification. The governing body for PC memory specifications, JEDEC, does not have an official spec for PC3200/DDR400 memory and therefore PC3200 modules are usually made up from hand picked PC2700 chip's that have been tested at 200mhz speeds on various platforms.
Today we're reviewing such a module - the TwinMOS PC3200 memory module. You will notice the module doesn't come with any heat spreaders, this isn't really essential but can help to push the memory past rated speeds.
This module is designed to run at 200mhz with a CAS Latency of 2.5. Looking on the TwinMOS web site, I found that the other memory timings should be set to
Precharge to Active (Trp) : 3T
Active to Precharge (Tras) : 6T
Active to CMD (Trcd) : 3T
DRAM Command Rate : 2T
Memory timings are another factor to be considered when going for as much memory bandwidth as possible. The difference between the slowest and fastest timings can be equivalent of up to 30 - 40 MHz of memory bus speed. With that in mind you should always try to run at a CAS Latency of 2, this has the most effect on improving performance. The DRAM command rate can also make a fair amount of difference, and you should try to set this to 1T.
One thing to note with the current crop of motherboards available for AMD platforms is that running the memory asynchronously to your FSB (Front Side Bus) is almost pointless, eg. 133Mhz FSB and 166Mhz for the memory - the gains are negligible. The CPU FSB is the primary bottleneck on this platform, and having that slower than your memory bus will result in very little gain. To gain any real benefit you need to unlock the processor multiplier, allowing you to achieve the same CPU MHz speed at a higher bus speed.
Once unlocked you can really begin to push the memory to its rated speeds (and beyond), allowing, for what you will shortly see, incredible gains in performance. On to the tests.....
Test System Specification
Athlon XP 2000+, Multiplier unlocked, Vapochill cooled in Project
Black Ice.
Abit AT7-MAX2 Motherboard
TwinMOS PC3200 CL2.5 DDR Memory
Corsair PC3200 XMS3202 CL2.0 Platinum Edition
Creative Geforce 4 TI4600 @ 360/770
80GB Maxtor 740DX Hard drive
The following software was used:
Windows XP Professional
Nvidia Detonator 40.71 Drivers
3D Mark 2001SE
Sisoft Sandra 2002
Pifast v41
Unreal Tournament 2003 Demo
Quake 3 Version 1.30, with AMD enhanced DLL's