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RAM latency refers simply to the ammount of clock cycles your RAM waits to do a particular task. with SDRAM (synchronous dynamic random access memory, not to be confised with the terms sdr or ddr which are both types of SDRAM) timming is everything, as the name "Synchronous" implies. because the RAM is dynamic, and not static (flash memory is a static memory) it requires constant "refreshing" of the data bits it has stored in its banks, refrsh "shots" of voltage going through it at a certain rate. obviously, the more often this refresh occurs, the less likely the RAM is to lose any data bits. the setting for refresh timmings add to latency.
this is one specific example of one of the timming settings, as there are others like RAS to CAS strobe, off the top of my head. last i looked, my motherboard had about 7 different timming settings i could change to effect latency.
the big one everyone usually refers to is CAS latency, and memory modules are usually rated by their "CAS latency". CAS stands for "column access strobe". RAS on the other hand stands for "Row Access Strobe". these points are completely trivial. your CAS latency tells you what your memory modules are rated to run at, and often times with quality name brand memory you can run the modules faster than what they are rated and they will work fine.
however, you never have to worry about setting the timmings because of the RAM's SPD (not sure what it stands for). the SPD settings are basically the default settings for timmings set in the memory module that it passes on to the motherboard, which in turn sets it to what you see when you look in the BIOS.
ok, now that allt hat is out of the way, setting your timmings.....
i can't tell you how many websites i have read, some really poor, some excellent references, about the virtues of tweaking your RAM timmings. out of all of the stuff i read, one thing i learned was that if you want it to work on your particular hardware, you need to set aside a bunch of time and caffine and play with the timmings. first of all, setting the timmings manually and not by SPD automatically enters you into the arena of guess work because there is no way to know whether your moduel will act the same as the guy next door's module of the same make and model. with silicon ic's, you're not going to be guarenteed to get identical quality from a single manufacturer, but instead they guarentee a minimum operating spec that it will definitely work at.
bottom line is though.... this isn't overclocking. adjusting your RAM timmings has a very, very low chance of damaging your system, and if it would damage anything it would be your operating system install, and i highly doubt you will do that. tweaking your timings will only change how the RAM adjusts to reads and writes, and if you set timmings that are not good for your system, the worst that will happen is a Blue Screen of Death/stop error. other side effects will be slow memory operation.
the way to go about this is to look in BIOS and see what defaults are, and write them down. then start with one setting at a time, see if you can get the machine to boot with the new timmings you set. if you can boot up, run a memory benchmark program to see how it performs. don't forget to benchmark your system at the default settings first and write down those results so you have a zero-point score to work from!
search the web for some tutorials that give explicit explanations on the timmings. the "BIOS guide" at adrian's rojak pot should still be out there, and it should have a nice explanation of all your particular motherboard manufacturer's naming convention for the memory timing settings.
alot of what i have read implies that certain settings rely on certain other settings, so finding a sweet spot combination of timmings usually ends up being what you need to do. there are some people out there who see these timmings in their heads, and know what goes with what and what ratios to shoot for. i am not one of those people.
also, the most common use for memory timmign tweaking is not to tweak the timmings to make the system faster, but pull the timmings back to make the system more stable when you are overclocking and want to hit the absolute tip of what your cpu can handle. consider this fact, because another thing i have read is that performance gains from memory timming tweaking alone are nowhere near that of straight overclocking. think of it like automotive racing.... yes, you can take a small 4 cylinder engine and change out the chip, do electronics work and modivy the intake system, even add a turbo..... but it aint gonna add horse power tot he same degree as dropping in a V*. the old addage of "there is no replacement for displacement" comes into play directly with the memory timmings, because you aren't adding any horsepower to your system when you do that.... you're just removing the top-speed governer, so to speak.
good luck!
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