Memory Latency Explained

zRoCkIsAdDiCtInG · 08-07-2005, 01:09 AM

I've noticed really that little people actually know that there is more to memory settings than just CAS Latency, and it's actually quite annoying, so I figured out that maybe I should just post a few bits of info to start them out, as well as inform them how to raise speed of their system through lowering or raising these settings, though I recommend not to toy unless you have experience or research the topic further.

So onto the basic settings:
------------------------------------------------------------------------
CAS Latency: This stands for Column-Access-Strobe
-The CAS Latency manages how fast memory units return a response to a data request. the settings range from 2 to 3, and lower settings provide speed gains, though the results make a small performance difference. The best performance gains are with SDR-RAM
------------------------------------------------------------------------
TRP: AKA RAS Precharge, has settings similar to TRCD, but has little significance on performance. It ranges from 2 to 4 and small performance gains are recieved from lower settings.
------------------------------------------------------------------------
tRAS: All Right, Bank cycle time is another name for tRAS, its the number of clock cycles needed to make the complete difference in charge between the bit and lines of referenceto restore data in the cells of memory. Settings range from 5 to 7, and with lower numbers, you recieve small performance gains.
------------------------------------------------------------------------
TRCD: This is known as RAS to CAS Delay, being numbered by clock cycles, and it possibly can limit the memory performance. It's measured from 2 to 4, and lower settings raise performance markedly.
------------------------------------------------------------------------
Bank Interleave: The setting that determines if memory is laced or not, it ranges from 0 to 2B to 4B and higher settings improve performance.
------------------------------------------------------------------------
CMD: One of the most powerful memory settings known as Command Rate, which ranges from 1T to 3T, lower settings increase performance noticeably.
------------------------------------------------------------------------
These are but mere basics if you want to know more about memory, but that drags you into reading about memory controllers and sequencing, which I won't get into (though I have so little of a life, I actually read a bit on these topics)

And now while others brag about low cas and we have a T1 command rate, we can secretly laugh at them. Then again, I recommend not to toy with these settings unless you know what consequences it may have on your PC

Welcome to the CAS Latency Rebellion

Please keep this thread on topic! anything off-topic will be deleted. Also Anti-Trend stuck the thread not me

Sniper

Exfoliate · 08-07-2005, 03:49 AM

Top notch post dude, that was very useful stuff as I practically fell into the party this post is directed at. I think this should be a sticky myself, if there was a pure memory thead you should be concidered as mod

zRoCkIsAdDiCtInG · 08-07-2005, 09:05 PM

I just hope that more people will understand more and stop ripping themselves off sometimes with the memory, and understand how it is,

expect more things like this, i'm writing a GPU one soon

"zRock's study guides" haha

max12590 · 08-07-2005, 09:17 PM

Well I also do some posting over at Hackthissite and there is this one guy named Pilot, he wrote like 30 page report on CPU's. It's really good. You can probably go over there and pm him for it. But yea, good work, the basics of RAM. The other thing that people don't realize is that overclocking RAM lessens your ability to overcolck their CPU. So they say I can only overclock 400 MHz, but if they run the RAM at 233 MHz with Hyper-Threading/Transport off or low they can get much higher.

zRoCkIsAdDiCtInG · 08-07-2005, 09:19 PM

yeah in to depth things will follow, im just writing the basics first

I bet I'll spend a good time on the following GPU guide

Exfoliate · 09-07-2005, 01:38 AM

Good, I'll be looking foward to that, I'll, uh, do an article on...pimp my rig

zRoCkIsAdDiCtInG · 11-07-2005, 05:29 PM

I finished the basics GPU guide, its mostly for newbs but I added in the pixel pipeline details of its process and will add in more, still newb or specialist, its worth the read.

zRoCkIsAdDiCtInG · 11-07-2005, 05:33 PM

Anti Trend stuck it? wow, I'm honored haha, hes like amazing (faints)

Exfoliate · 11-07-2005, 08:32 PM

Woah, sorry Sniper, and good work AT, I forgot Mod's had that kind of power. I'll try to keep things on target, it's just so hard...
Do you have any other guides planned Z?

zRoCkIsAdDiCtInG · 11-07-2005, 11:47 PM

the video one came out kind of cruddy, i'm working on fixing it up, so everyone expect a complete makeover

yeah, probably ever major pc component

basics
and optimization probably

vol7ron · 02-08-2006, 01:40 AM

Nice, but you have the order mixed up. As well as a few other things.

Its normally:
CL-tRCD-tRP-tRAS-CMD

Written out:
CAS Latency-RAS to CAS Delay-RAS Precharge-Active to Precharge Delay-Command Rate

Defined:
CL-time between a command sent to memory from the proc and when it is replied to
tRCD-time between accessing row and column in memory (addresses are stored in a table kinda like an Excel Spreadsheet)
tRP- time between disabling a line of data and accessing another line
tRAS- how long memory has to wait until next access to memory can be started
CMD- time it takes between the mem chip being activated and when the first command may be sent to memory (memory is activated first and then a command is sent to it) Unlike the above this is normally in just T1 or T2 where the numbers are defined in clock cycles (T1 = 1 clock cycle; T2 = 2 clock cycles)

I have notice a considerable difference in CAS latency (as most people do) just from going from 3 to 2.5. All the other timings DO matter. A general rule I use when just glancing is to add up the 4 numbers and get the lowest one (like a golf score). The middle 2 numbers you can generally use interchangeably 2-4-3-7 = 2-3-4-7 in my opinion.

THE MOST IMPORTANT THING: Test your memory. Using Memtest or SiSoftware Sandra2007 (my pick). People are usually concerned with overclocking their memory. But I've seen better improvement in going for the lowest timing and then raising the clock speed (like around 350MB/s improvement in bandwidth with Kingston ValueRAM). In my opinion, Never turn off HyperThreading just to raise your clock speed or lower your memory timings, I've tested it - it sucks (lowered bandwidth by like 2GB/s)

Didn't mean to step on anyones toes, but just wanted to clarify and correct some things.

T Vlasceanu · 15-09-2006, 07:14 PM

Thank you kindly. This information is very usefull for me. Great site! Thanks again!

Ashton · 16-02-2008, 06:43 AM

Thanks, this is pretty useful. Would buying low-latency ram increase performance much?

Big B · 18-02-2008, 10:24 PM

Depends on the CPU. These days, timings don't seem to be as important as much as the performance of the CPU. However, if you're into overclocking, lower latencies may translate into higher clocking RAM than something with a slower timing.

For DDR2, 4-4-4 timings are pretty low. I'm not sure if you'll see faster than 3-3-3 timings, but that wasn't the goal of DDR2. Higher speed was, and while lower latencies could probably be achieved, I'm not sure it'd be at a price people would want. For example, I have 2GB of OCZ DDR2 PC6400 (DDR2-800) coming in a few days that cost me less than $50. It's timings are fairly slow at 5-5-5, but moving to CAS 3 would either raise the price roughly $25 or force me to go with some PC2-5300 (DDR2-667). There's also some Corsair DHX that's running over $200, but not everybody wan'ts to pay that kind of cash. I can't imagine DDR2-1066 CAS3 coming under $100 anytime soon. Granted, memory prices have dropped (I pad almost $100 for my Crucial Ballistix PC3200 1GB kit over a year ago).

Ashton · 18-02-2008, 11:27 PM

Well I found a cheap 2GB Corsair DHX for $70, it has 4 4 4 12 timings, runs at 800mhz and includes heatsinks.

So I'll probably order that, thanks for the help

08-07-2005, 01:09 AM	#1 (permalink) Top
zRoCkIsAdDiCtInG HWF Guitar Freak Join Date: Apr 2005 Gender: Male Posts: 1,487 Times Helpful: 101 My Mood: Amused Status: Offline My Computer	Memory Latency Explained I've noticed really that little people actually know that there is more to memory settings than just CAS Latency, and it's actually quite annoying, so I figured out that maybe I should just post a few bits of info to start them out, as well as inform them how to raise speed of their system through lowering or raising these settings, though I recommend not to toy unless you have experience or research the topic further. So onto the basic settings: ------------------------------------------------------------------------ CAS Latency: This stands for Column-Access-Strobe -The CAS Latency manages how fast memory units return a response to a data request. the settings range from 2 to 3, and lower settings provide speed gains, though the results make a small performance difference. The best performance gains are with SDR-RAM ------------------------------------------------------------------------ TRP: AKA RAS Precharge, has settings similar to TRCD, but has little significance on performance. It ranges from 2 to 4 and small performance gains are recieved from lower settings. ------------------------------------------------------------------------ tRAS: All Right, Bank cycle time is another name for tRAS, its the number of clock cycles needed to make the complete difference in charge between the bit and lines of referenceto restore data in the cells of memory. Settings range from 5 to 7, and with lower numbers, you recieve small performance gains. ------------------------------------------------------------------------ TRCD: This is known as RAS to CAS Delay, being numbered by clock cycles, and it possibly can limit the memory performance. It's measured from 2 to 4, and lower settings raise performance markedly. ------------------------------------------------------------------------ Bank Interleave: The setting that determines if memory is laced or not, it ranges from 0 to 2B to 4B and higher settings improve performance. ------------------------------------------------------------------------ CMD: One of the most powerful memory settings known as Command Rate, which ranges from 1T to 3T, lower settings increase performance noticeably. ------------------------------------------------------------------------ These are but mere basics if you want to know more about memory, but that drags you into reading about memory controllers and sequencing, which I won't get into (though I have so little of a life, I actually read a bit on these topics) And now while others brag about low cas and we have a T1 command rate, we can secretly laugh at them. Then again, I recommend not to toy with these settings unless you know what consequences it may have on your PC Welcome to the CAS Latency Rebellion Please keep this thread on topic! anything off-topic will be deleted. Also Anti-Trend stuck the thread not me Sniper __________________ Last edited by zRoCkIsAdDiCtInG; 08-07-2005 at 01:18 AM.

08-07-2005, 03:49 AM	#2 (permalink) Top
Exfoliate Captain Dial-up Join Date: Jan 2005 Age: 19 Male Posts: 4,258 Times Helpful: 223 Status: Offline My Computer	Top notch post dude, that was very useful stuff as I practically fell into the party this post is directed at. I think this should be a sticky myself, if there was a pure memory thead you should be concidered as mod __________________

08-07-2005, 09:05 PM	#3 (permalink) Top
zRoCkIsAdDiCtInG HWF Guitar Freak Join Date: Apr 2005 Gender: Male Posts: 1,487 Times Helpful: 101 My Mood: Amused Status: Offline My Computer	I just hope that more people will understand more and stop ripping themselves off sometimes with the memory, and understand how it is, expect more things like this, i'm writing a GPU one soon "zRock's study guides" haha __________________

08-07-2005, 09:17 PM	#4 (permalink) Top
max12590 Masterful Geek Join Date: Nov 2004 Age: 17 Male Posts: 1,016 Times Helpful: 76 Status: Offline My Computer	Well I also do some posting over at Hackthissite and there is this one guy named Pilot, he wrote like 30 page report on CPU's. It's really good. You can probably go over there and pm him for it. But yea, good work, the basics of RAM. The other thing that people don't realize is that overclocking RAM lessens your ability to overcolck their CPU. So they say I can only overclock 400 MHz, but if they run the RAM at 233 MHz with Hyper-Threading/Transport off or low they can get much higher. __________________ In the words of a certain Battlefield 2 commander, "They're spawnin' like crazy at the Gas Station and then tryin' to Forrest Gump it down the Interstate." Last edited by max12590; 08-07-2005 at 09:19 PM.

08-07-2005, 09:19 PM	#5 (permalink) Top
zRoCkIsAdDiCtInG HWF Guitar Freak Join Date: Apr 2005 Gender: Male Posts: 1,487 Times Helpful: 101 My Mood: Amused Status: Offline My Computer	yeah in to depth things will follow, im just writing the basics first I bet I'll spend a good time on the following GPU guide __________________

09-07-2005, 01:38 AM	#6 (permalink) Top
Exfoliate Captain Dial-up Join Date: Jan 2005 Age: 19 Male Posts: 4,258 Times Helpful: 223 Status: Offline My Computer	Good, I'll be looking foward to that, I'll, uh, do an article on...pimp my rig __________________

11-07-2005, 05:29 PM	#7 (permalink) Top
zRoCkIsAdDiCtInG HWF Guitar Freak Join Date: Apr 2005 Gender: Male Posts: 1,487 Times Helpful: 101 My Mood: Amused Status: Offline My Computer	I finished the basics GPU guide, its mostly for newbs but I added in the pixel pipeline details of its process and will add in more, still newb or specialist, its worth the read. __________________

11-07-2005, 05:33 PM	#8 (permalink) Top
zRoCkIsAdDiCtInG HWF Guitar Freak Join Date: Apr 2005 Gender: Male Posts: 1,487 Times Helpful: 101 My Mood: Amused Status: Offline My Computer	Anti Trend stuck it? wow, I'm honored haha, hes like amazing (faints) __________________

11-07-2005, 08:32 PM	#9 (permalink) Top
Exfoliate Captain Dial-up Join Date: Jan 2005 Age: 19 Male Posts: 4,258 Times Helpful: 223 Status: Offline My Computer	Woah, sorry Sniper, and good work AT, I forgot Mod's had that kind of power. I'll try to keep things on target, it's just so hard... Do you have any other guides planned Z? __________________

11-07-2005, 11:47 PM	#10 (permalink) Top
zRoCkIsAdDiCtInG HWF Guitar Freak Join Date: Apr 2005 Gender: Male Posts: 1,487 Times Helpful: 101 My Mood: Amused Status: Offline My Computer	the video one came out kind of cruddy, i'm working on fixing it up, so everyone expect a complete makeover yeah, probably ever major pc component basics and optimization probably __________________

02-08-2006, 01:40 AM	#11 (permalink) Top
vol7ron Banned Join Date: Aug 2006 Posts: 153 Times Helpful: 20 My Mood: Amused Status: Offline	Nice, but you have the order mixed up. As well as a few other things. Its normally: CL-tRCD-tRP-tRAS-CMD Written out: CAS Latency-RAS to CAS Delay-RAS Precharge-Active to Precharge Delay-Command Rate Defined: CL-time between a command sent to memory from the proc and when it is replied to tRCD-time between accessing row and column in memory (addresses are stored in a table kinda like an Excel Spreadsheet) tRP- time between disabling a line of data and accessing another line tRAS- how long memory has to wait until next access to memory can be started CMD- time it takes between the mem chip being activated and when the first command may be sent to memory (memory is activated first and then a command is sent to it) Unlike the above this is normally in just T1 or T2 where the numbers are defined in clock cycles (T1 = 1 clock cycle; T2 = 2 clock cycles) I have notice a considerable difference in CAS latency (as most people do) just from going from 3 to 2.5. All the other timings DO matter. A general rule I use when just glancing is to add up the 4 numbers and get the lowest one (like a golf score). The middle 2 numbers you can generally use interchangeably 2-4-3-7 = 2-3-4-7 in my opinion. THE MOST IMPORTANT THING: Test your memory. Using Memtest or SiSoftware Sandra2007 (my pick). People are usually concerned with overclocking their memory. But I've seen better improvement in going for the lowest timing and then raising the clock speed (like around 350MB/s improvement in bandwidth with Kingston ValueRAM). In my opinion, Never turn off HyperThreading just to raise your clock speed or lower your memory timings, I've tested it - it sucks (lowered bandwidth by like 2GB/s) Didn't mean to step on anyones toes, but just wanted to clarify and correct some things. Last edited by vol7ron; 08-08-2006 at 11:21 PM.

15-09-2006, 07:14 PM	#12 (permalink) Top
T Vlasceanu Geek Trainee Join Date: Sep 2006 Posts: 1 Status: Offline	Thank you kindly. This information is very usefull for me. Great site! Thanks again!

16-02-2008, 06:43 AM	#13 (permalink) Top
Ashton Geek Join Date: Feb 2008 Gender: Male Posts: 86 Times Helpful: 4 My Mood: Fine Status: Offline My Computer	Thanks, this is pretty useful. Would buying low-latency ram increase performance much? __________________

18-02-2008, 10:24 PM	#14 (permalink) Top
Big B HWF Godfather Join Date: Dec 2001 Age: 27 Male Posts: 9,546 Times Helpful: 584 My Mood: Devilish Status: Offline My Computer	Depends on the CPU. These days, timings don't seem to be as important as much as the performance of the CPU. However, if you're into overclocking, lower latencies may translate into higher clocking RAM than something with a slower timing. For DDR2, 4-4-4 timings are pretty low. I'm not sure if you'll see faster than 3-3-3 timings, but that wasn't the goal of DDR2. Higher speed was, and while lower latencies could probably be achieved, I'm not sure it'd be at a price people would want. For example, I have 2GB of OCZ DDR2 PC6400 (DDR2-800) coming in a few days that cost me less than $50. It's timings are fairly slow at 5-5-5, but moving to CAS 3 would either raise the price roughly $25 or force me to go with some PC2-5300 (DDR2-667). There's also some Corsair DHX that's running over $200, but not everybody wan'ts to pay that kind of cash. I can't imagine DDR2-1066 CAS3 coming under $100 anytime soon. Granted, memory prices have dropped (I pad almost $100 for my Crucial Ballistix PC3200 1GB kit over a year ago). __________________ Hardware Forums\|HWF Rules\|My DVD's\|PSU FAQ\|HWF Folding Team\|2CPU

18-02-2008, 11:27 PM	#15 (permalink) Top
Ashton Geek Join Date: Feb 2008 Gender: Male Posts: 86 Times Helpful: 4 My Mood: Fine Status: Offline My Computer	Well I found a cheap 2GB Corsair DHX for $70, it has 4 4 4 12 timings, runs at 800mhz and includes heatsinks. So I'll probably order that, thanks for the help __________________

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
SoundBlaster Live! Latency	loafofbread3	Sound Cards and Speakers	1	17-06-2005 04:07 PM
Memory LED	gumdigger	General Hardware	6	03-04-2005 12:27 PM
Checking RAM Latency	undefined	CPU, Motherboards and Memory	1	26-03-2005 03:21 PM
PCI Latency Tool 2.0	syngod	General Software	2	12-01-2005 11:28 PM
Cas Latency?	FishyWishy	Overclocking & Cooling	3	08-04-2004 01:28 PM