Memory Timings

[jamesro]

I read this in the Read before you post as i was wanting to know more about RAM and specifically Timings and what they mean. I read it a few times and dont really understand it.
like what determines these settings? is it the memory controller and it is restricted by the RAM modules?
what would be "great" timings for ddr2 800 ram?
3-3-2-6 ? can any no.s be replaced in the sequence?

Q: How does memory access work, and what do the timings stand for?
A:
MEMORY ACCESS:
1. tRCD (RAS to CAS Delay) 2-3 cycles, The row is selected by the Memory Controller.
2. CAS (Column Address Strobe) 2,2.5,3 cycles (DDR), The Memory Controller selects the column and now the ROW is
ACTIVE, and the READ COMMAND is sent.
3. Data is sent to the DQ pins after CAS delay.
4. tRAS (Row address Strobe) 6 cycles, The module waits a certain period of time for the data to be active.
5. tRP (RAS precharge) 2 cycles, The Memory Controller DEACTIVATES the row.
6. Memory Cycle repeats as requested by the Memory Controller.

The timings are represented as follows:
2-3-2-6 1T (CAS, tRCD, tRP, tRAS)

thanks for trying to help me understand

 

[Mondoman]

With current RAM modules, the memory controller normally can handle faster timings than the modules, so the modules limit the possible timings.
Corsair has a nice multimedia explanation of how memory works on their website.

 

[akhilles]

To oversimplify, the lower the latency, the faster & more expensive the ram. You have to take into account the rated frequency (mhz). 3-3-2-6 800Mhz will cost quite a bit of money.

http://en.wikipedia.org/wiki/SDRAM_latency#SDRAM_access

 

[jamesro]

thanks for the reply
so lower no.s BETTER more MULAH etc. down to real world apps such as games etc is there a NOTICEABLE difference in performance i.e how severely can a games FPS performance be affected if u have both 800Mhz Modules but with lets say one has HIGH END specs and the other below average.
or these timings really only affect if u want to overclock the RAM?

thanks for those links.

 

[jamesro]

i copied this off wiki.
"Although the SDRAM latency timing can be adjusted manually, using lower latency settings than the module's rating (overclocking) may cause a computer to crash or fail to boot."
If you alter one value of the ram settings do the other 3 have to be changed as well in the same instance?

 

[Mondoman]

Normally there is no noticeable difference in performance w/Intel CPUs.

 

[akhilles]

wiki is right. If say my 4-4-4-12 is set to 2-2-2-8, it won't do. 3-3-3-8@2.4v maybe. Either you test it yourself or google for results.

Not to your naked eyes. Benchmarks will show a difference. If you do time-consuming tasks, it will show. Daily tasks like web browsing, reading a document, no.

 

[jamesro]

so for example if stock ram timings were 5-5-5-10
can u alter it one setting at a time? example 3-5-5-10?
or if one value changes the whole timing has to be modified accordingly such as 3-3-3-8
or something or other these no.s are just purely for a demonstration purpose.

 

[jsc]

If your motherboard allows, each can be changed independently.

In my case, I have DDR2-1000 ram. I plugged it into my motherboard, and the timing defaulted to 5-5-5-15-2t. Initially, I was overclocking from 266 MHz (DDR2-533) to 366 MHz (3.3GHz CPU core, DDR2-733). With the overspec'ed ram, I was able to drop my memory timing to an impressive sounding 3-3-3-6-1t. Memory i/o increased 6% - unnoticeable in anything other than benchmarks. Was the extra perfomance worth the extra money I paid for the memory? Frankly, no. But I was looking forward to Penryn when I bought the parts last year.

Recently upgraded HSF. I am now running at 400 MHz. FSB (DDR2-800 equivalent). I am running more conservative mem. timings now while I test for stability.

 

[jamesro]

so in short...
are you trying to say overclocking memory is kinda waste of effort?

 

[akhilles]

Not really. it's good for:

education
fun
bragging rights

What else?

 

[jamesro]

wat ddr2 modules would u recommend for overclocking?
are there ones that are noob friendly

 

[jsc]

I do not think that I'm OC'ing memory. I am really not running it faster than it was designed for. Four cycles at 800 MHz (400 MHz FSB) take the same amount of (real) time as 5 cycles at 1000 MHz (500 MHz FSB).

At the time that I bought my parts (Dec 06), I was thinking about upgrading to Penryn if it was cost effective. My motherboard FSB tops out at 450 MHz (DDR2-900). So theoretically, I could reach 4 GHz with any CPU running a X9 internal multiplier.

What does that get me? Well, the difference between Conroe at 3.6 GHz and Penryn at 4 GHz will probably be noticeable only in benchmarks. And since at the upper end, games are mostly GPU bound, it probably won't help much there. Like akhilles said, it gets me "education, fun, and bragging rights".

It's far more practical for me to drop a Penryn quad core into the motherboard. In my case, I spent about $60 extra on overspec'ed memory that I didn't need.

jamesro:
It's not a matter of memory being "noob friendly" as the motherboard. I have no experience will other brands (maybe some of the others can help), but the eVGA 680i was easy to work with. When I was overclocking and went too far, the PC would lock up. After rebooting, the motherboard automatically defaulted to stock CPU FSB. The same happened with memory timing. The system would lock up. After rebooting, the BIOS automatically lowered the memory clock.

This was handy for two reasons. I never had to clear CMOS. And the BIOS screens always indicated whether the problem was CPU or memory. I do not know how other motherboards act.

This was like directions that say, "If you see a MacDonalds on your left, you went too far. Backup two blocks and turn left." I saw that MacDonalds a lot.

 

[jsc]

wat ddr2 modules would u recommend for overclocking?

Forgot to answer this, apologies. In a way it's a non-answer. I am trying to show you how I decide what I am going to do.

You have a lot of choices. I have a preference for Crucial. But if you ask 10 different people, you will be lucky to get only 5 different answers.

First, check what your motherboard manufacturer recommends. That doesn't mean that other brands won't work. But it's a starting point. Check the appropriate forums here: "Will this work with that?" Then go to newegg. Check specs, prices, and the user reviews.

Here's how I use the reviews. I usually ignore or discount the 5 star reviews. They are usually variations of, "Works great!!! Best thing since sliced bread." 4 star reviews are usually variations of, "Works good. Worth the money." 1 star reviews are usually variations of, "This product sucks."

I pay the most attention to the 2 and 3 star reviews and the 1 star reviews that say, "This product sucks because ..." These indicate problems, sometimes very serious. The problems can range from someone getting a DOA part (can happen to anyone) to problems indicating serious incompatibilities. Sometimes a review highlights a problem you will be willing to overlook or doesn't apply to you.

I do tend to read the longer reviews because they contain more information: "This is great, good , or bad because ..."

Then come back here. Your original question shows a common "noob" tendency. It does not contain enough information for a useful answer. This would be better: "Memory recommendations for <CPU model>, <motherboard model>, how much overclocking (none, moderate, or to the limit), purpose, and budget."

Remember, we were all noobs at one time.

 

[jamesro]

thanks for your thorough input get back to you soon