timings and latencies

puma luke said:
can anybody put in simple terms what these are all about? ive read the sticky on ram an its still unclear. im maybe looking at tweaking my ram.
cheers:)
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Which ones are you particulary interested in, and what exactly do you want to know?

The sticky is a bit old now, and some of the issues it discusses are long since gone, but mostly it's still pretty valid.

The memory timings are the number of clock cycles between a pulse of power to the functions (for want of a better word) on chip. Each function can only be accessed on the pulse. (hmmm! that's really simplified, but hopefully still slightly accurate).

There are loads more memory timings than the few usually quoted, but the quoted timings have the most significance.

cutted and pasted of various wiki pages said:
tCAS The number of clock cycles needed to access a certain column of data in SDRAM. CAS latency, or simply CAS, is known as column address strobe latency, sometimes referred to as tCL.

tRCD (RAS to CAS Delay) The number of clock cycles needed between a row address strobe (RAS) and a CAS. It is the time required between the computer defining the row and column of the given memory block and the actual read or write to that location. tRCD stands for row address to column address delay.

tRP (RAS Precharge) The number of clock cycles needed to terminate access to an open row of memory, and open access to the next row. Stands for Row precharge time.

tRAS (Row Active Time) The minimum number of clock cycles needed to access a certain row of data in RAM between the data request and the precharge command. It's known as active to precharge delay. According to Mushkin, in practice for DDR SDRAM, this should be set to at least tRCD + tCAS + 2 to allow enough time for data to be streamed out.
RAM speeds are given by the four numbers above, in the format "tCAS-tRCD-tRP-tRAS".

So, for example, latency values given as 2.5-3-3-8 would indicate tCAS=2.5, tRCD=3, tRP=3, tRAS=8
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Lower numbers = faster, but some have more impact than others.

note that the numbers given are in clock cycles, not absolute times, so some memory looks slower on paper, but when put in a faster machine the actual latencies may be lower.

I have't played around with chip timings for ages, and mostly only needed to do so when really trying to eke out the last few Hz out of an overclock. Usually I left them nearish stock timings as I seldom run a long term build at Max clock.

There should be loads of helpful but complex info in the Net, but it might be a steep learning curve if you haven't a lot of background in it yet.
 
puma luke said:
hm right ok then thanks, so where would i start then when overclocking?
say for example it is 7-7-7-20 would i lower all of the 7's to 6's or just one at a time or something?
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If you that most probably your PC won't boot. You need to strike a balance between Speed, Voltage, and Timings. Generally it's something like this:

More Speed = More Voltage = Higher Timings

Otherwise you're PC won't be stable, unless you've got some special high-grade-uber-overclockable set of RAM :)
 
puma luke said:
think im gonna leave it for a while until i actually understand how it all works... not like its slow a it is.
cheers:)
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That's probably for the best for now. If you want to clock your kit, I would recommend staying at spec for memory timings to start with.

And, only change one thing at a time when you are experimenting. If you change lots of things at the same time, you will have no idea what the problem is when something stops working.
 
In my experience, timings make no difference any longer. When it was C3 to C2 it made a big difference, but proportionately, there is a much smaller difference between C7 C8 and C9 and frequency is far more important IMO. The other timings have never made any difference outside of benchmarks really, and even then it was VERY minimal.
 
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