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Corsair Twin2X DDR2 5400C4 ProSeries Review
Author: Dennis Garcia
Published: Thursday, October 21, 2004
Memory timings
Why is it important to have paired modules? In a word, timings. Every memory module is assigned a speed rating that is programmed into a little chip called a SPD. The memory controller uses this information to determine how fast data will flow in and out of the memory module. While these settings can be overridden in the motherboard BIOS it is not recommended since any change can adversely effect system stability.
To better understand how this effects your computer you need to know a little bit about timings though generally speaking: "lower timings + higher speed = good".
Why does this matter? Well, for everyday usage like web surfing and general 2d office apps it doesn't, and any increase in speed you will not notice. Low timings really come into play while running memory intensive application like games, graphics and program development. The lower the timings, the faster data can be processed, and the faster the task can be completed. Of course the speed of the operator will remain unaffected.
To better understand how this effects your computer you need to know a little bit about timings though generally speaking: "lower timings + higher speed = good".
Why does this matter? Well, for everyday usage like web surfing and general 2d office apps it doesn't, and any increase in speed you will not notice. Low timings really come into play while running memory intensive application like games, graphics and program development. The lower the timings, the faster data can be processed, and the faster the task can be completed. Of course the speed of the operator will remain unaffected.
The termonlogy used to describe overall memory performance is divided up into 4 key timings. (CAS, T(RAS) T(RCD) T(RP)). These all define how fast a memory module will operate and luckily for us DDR1 terminology also applies to DDR2.
Memory Timing Terms
CAS Latency: is a number that refers to the rounded ratio between column access time and the clock cycle time. A CAS Latency of 2 @ 200Mhz would look like this
CAS 2 = 10ns (column access time) / 5ns (clock cycle time @ 200Mhz)
Clock Cycle Times
5ns = 200Mhz
6ns = 166Mhz
7.5ns = 133Mhz
10ns = 100Mhz
The relative constant in the equation is Column Access Time. This number will have an effect on the CAS number as the Clock Cycle Time changes.
T(RAS) Active to Precharge: T(RAS) specifies the amount of time required between an active command to a precharge command. Basically this means the number of cycles that must pass after a bank is opened to when it can be closed. Lower is better.
T(RCD) Active to CMD: T(RCD) Is the time we have to wait between a row access request and a column access request. Also can be called RAS-to-CAS, this number should be the same as your CAS Latency number for the best speed.
T(RP) Precharge to Active: The amount of time from a bank precharge request to when it can be activated.
CAS 2 = 10ns (column access time) / 5ns (clock cycle time @ 200Mhz)
Clock Cycle Times
5ns = 200Mhz
6ns = 166Mhz
7.5ns = 133Mhz
10ns = 100Mhz
The relative constant in the equation is Column Access Time. This number will have an effect on the CAS number as the Clock Cycle Time changes.
T(RAS) Active to Precharge: T(RAS) specifies the amount of time required between an active command to a precharge command. Basically this means the number of cycles that must pass after a bank is opened to when it can be closed. Lower is better.
T(RCD) Active to CMD: T(RCD) Is the time we have to wait between a row access request and a column access request. Also can be called RAS-to-CAS, this number should be the same as your CAS Latency number for the best speed.
T(RP) Precharge to Active: The amount of time from a bank precharge request to when it can be activated.
For more information check out the articles below from Corsair http://www.corsairmemory.com/main/trg-cas.html
