BIOS from A to Z

26. Change RAM Timing Settings

Every SDRAM and DDR memory module includes a Serial Presence Detect (SPD) chip, which stores memory timing values settings. RAM vendors specify SPD values designed to guarantee safe, stable operation. Most of the time, however, it’s worthwhile to experiment with tighter timing values, as this can improve overall performance by as much as 10%.

The relevant option may be named something like "System Performance", "Memory Timings", or "Configure DRAM Timing". As a rule, the default value for this option is "By SPD". This instructs the computer to read recommended timing values right from the memory module itself, and to automatically use those values for memory access. The alternate value "Enabled" is likewise unlikely to cause problems for your PC.

Those who want to tweak their systems for speed should instead select the values "Disabled" or "User Defined" if and when they’re available (see Screenshot K.) Then set the parameter values yourself, as described in the tips that follow next.

27. Lower The RAS-to-CAS Delay Value

It’s best to think of system memory as a kind of two-dimensional table. Accessing data first requires identifying a row using a signal called Row Address Strobe (RAS) and then a column using Column Address Strobe (CAS), to uniquely identify a specific memory location. A pause is required between the RAS signal and the CAS signal, to be sure that memory is correctly addressed. This RAS-to-CAS delay normally consumes two or more clock cycles.

The value for the "SDRAM RAS to CAS Delay" lets you specify exactly how many clock cycles must elapse between sending a RAS signal and then following with a CAS signal. Possible settings usually fall in a range from 2 to 5, where 2 is fastest. Reduce this value one cycle at a time, and test your system for stability with each change. The better the RAM, the smaller the value at which your system will keep working properly.