Read Preamble Time

Common Options : 2.0 to 9.5 in increments of 0.5, Auto

Quick Review

This is an AMD Athlon 64 / Opteron processor-specific BIOS feature. It controls the amount of read preamble, a period during which the processor's built-in memory controller intentionally delays the activation of its data strobe receiver to prevent data corruption. You are allowed to manually set the amount of read preamble (in nanoseconds) or leave it at Auto.

If you wish to set it manually, you will need to calculate the appropriate amount of read preamble. This is normally done by trial and error, keeping in mind the distance of the furthest memory module, clock speed and type of memory module used. AMD recommends the following values for DDR memory.

Do note that these values are rough recommendations by AMD and assume that the furthest DIMM slot is occupied by a module. If your motherboard has four slots and you choose to populate only the first two slots, you can use a shorter read preamble.

You can set the read preamble as low as possible for maximum performance but you run the risk of data corruption and system instability. So, it's generally recommended you stick with the preamble time recommended by AMD (see table above) or your memory module's manufacturer.

You can, of course, adjust the read preamble according to the situation. For example, if you are overclocking the memory modules, or if you populate the first two slots of the four available DIMM slots; you can get away with a lower read preamble.

When set to Auto, the processor will query the memory modules' SPD chip and use the highest value it finds. This is the safest option.

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