The type of memory in PC's today is called DDR. A memory module is described with TYPE SIZE SPEED and TIMINGS. A example is a memory module with DDR3 2048MB 1333MHZ 9-9-9-24.
Type can be DDR1 to DDR4. Higher is generally better and faster than a lower number. What type of memory one can use depends on the motherboard and they are not compatible with each other.
How much memory a module contain. In MB or GB.
The maximum memory speed the memory support. Each DDR type have a span that is possible. Higher is better.
Show how long time a memory takes to perform access operations. Listed in order of importance and they are called CL, TRCD, TRP and TRAS. Listed as numbers separated with dash, 9-9-9-24. Each number list how many clock cycles a certain memory operations take. Newer DDR types have higher access times but they also run at a faster clock speed so the overall time gets lower.
CL: CAS Latency
How long does it take to access each column.
TRCD: Ras to CAS delay
When a RAS have been set how long does it need to wait.
TRP: RAS Precharge.
How long does i take to deactivate a selected row.
TRAS: active-to-precharge delay
Minimum time that a row needs to be active.