RAM manufacturers typically list the recommended timing for their RAM as a series of four integers separated by dashes (e.g 2-2-2-6 or 3-3-3-9 or 4-4-4-12 and so on). While there are many other settings related to RAM, these four integers refer to the following settings, which are typically listed in this order: CL - TRCD - TRP - TRAS.
CL = CAS Latency time: The time it takes between a command having been sent to the memory and when it begins to reply to it. It is the time it takes between the processor asking for some data from the memory and it returning it.
TRCD = DRAM RAS# to CAS# Delay: The number of clock cycles performed between activating the Row Access Strobe and the Column Access Strobe. This parameter relates to the time it takes to access stored data.
TRP = DRAM RAS# Precharge: The amount of time between the 'precharge' command and the 'active' command. The 'precharge' command closes memory that was accessed and the 'active' command signifies that a new read/write cycle can begin.
TRAS = Active to Precharge delay: The total time that will elapse between an active state and precharge state. This is the sum of the previous timings: CL + TRCD + TRP.
The BIOS on a PC may allow the user to make adjustments to RAM Timing in an effort to increase speed (with possible risk of decreased stability) or, in some cases, increase stability (by lowering the speed).
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