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View Full Version : Do memory timings make a difference to performance?


Cabal
27-03-2003, 01:53 PM
Just curious as to how much of a difference using the faster memory timings make?

I am after some new memory for my nforce 2 board and want to know if its worth shelling out an extra cash for slight faster timings?

KingJackal
27-03-2003, 02:23 PM
They'll likely only affect memory bandwidth by around 5% at the most. MHz is always better than timings. You always crank your timings up ( ie, slow ), then OC to your max speed, THEN start tweaking timings down - as performance-wise they're more just a nice bonus.

But that's hardly the point. RAM that's rated for better timings almost always is capable of more MHz.... ;)

And besides, if you have have bottleneck part limiting your MHz ( CPU, mobo, PCI cards, whatever ), then any performance boost past that has to be gained off timings. For example, my old KK266+ board could only do 165MHz fsb, no more. So if I wanted more performance from my RAM, it had to be via the timings on the RAM.

Oh yeah, and it gives you wankFactor++ <-- real reason ;)

_N_
27-03-2003, 02:28 PM
nah, I found that with better memory timings, my seti crunching improved quite a bit,

but in games etc, it's only a little improvement, but things which use the RAM a lot benefit more 5% sometimes.

I personally, only get RAM that can handle the hardest timings, but I don't up the MHz up much cause I can't cause of my mobo.

ExtremE
27-03-2003, 03:06 PM
If it is for the nforce 2 boards then u prob have the Dual Channel ram slots
witch means if u get the dual channel ram u double the memory bandwidth (this is what ppl say wiether or not it does double it i dont know i will be doing this next week hopefully)
and as far as i know the GEIL Dual Channel 512MB (2x 256MB) PC3200 5ns GL2000 Chip ULTRA CAS 2 6-3-3 1T with Pure Copper Plate
is the only ram that does it but im sure corsair and other rams will do it to but be alot more


the GEIL Dual Channel ram cost $309 from dragon pc :)

k14
27-03-2003, 05:41 PM
*sits and waits for flaming to start*:D

_N_
27-03-2003, 05:51 PM
yeah, I was gonna point that out in a nice way, but can't be stuffed. :rolleyes:

Tiggerz
27-03-2003, 08:12 PM
You guys need to be a little more accurate as to what you are calling dual channel ram and what you aint.

Geil PC3200 is NOT dual channel ram. Its dual sided DDR400 ram. Completely different.

Geil PC3500 IS Dual Channel ram, otherwise officially known as DDR434.

You can't put DDR434 in a normal memory slot. You need a specially built board for it.

As to what difference it will make. DDR400 is designed to run at CAS 3.0 and all the testing I have seen shows it working best at this speed.

The Chipsets used on mainboards are designed to run at certain CAS settings for optimum performance. Intel P4s up to and including the Granit Bay chipset work best at CAS 2.5.

Drop below this and you introduce a phenominum known as ram timing bottleneck. That is, if you go to CAS 2.0 you will probably end up with performance akin to CAS 4.0 if there was such a thing.

When I overclock my ram, I usually slow it down to CAS 3.0. I have Kingston DDR333 running as DDR400 set at 3-3-3-8 for memory timings and 2.7v. How I got this was basically by looking at the JDEC specs for DDR400 and setting my system to that.

fraz
28-03-2003, 10:57 AM
You can get 512 sticks of ddr434 (99% sure its kingston) from techpac for around $180

Cabal
28-03-2003, 01:26 PM
What proof do you have of this Tiggerz?

You are the only person I have ever seen say to slow down the ram excluding the ppl who do it for stability reasons.

So when I buy the uber expensive corsair 2 2 2 5 ram I am wasting my time because I should be running it at 3 3 3 8 which any $80 stick can do?

Sounds a bit crazy to me :)

Geek4Life
28-03-2003, 01:52 PM
I think that would only be the case if errors were happening with the aggressive memory settings.

ExtremE
28-03-2003, 02:01 PM
this website is the geil dual channel website and there is 3200 dual channel ram on it
http://www.geilusa.com/proddetail.asp?linenumber=18


i dont really know too much about dual channel what evers i just going from what i have read

Tiggerz
28-03-2003, 07:19 PM
The PC3200 listed on that side is DDR400 (not dual channel).. Its just tidied up a bit so you can run it on a dual channel board (as normal ram).

The stuff listed below that on the website is the dual channel stuff.

Although it being CAS 2 means that I wouldnt touch it. JDEC specifiy quite explicity that it needs to be CAS 3.

The following is a rather loose definition.

The best way of thinking about ram timings is to use ethernet as an example.

If two people transmit data at the same time, you get a data collision. Then the ligitimate tranmitter has to resend. The effect is that the data takes twice as long to get to its destination.

Memory architecture is kind of the same. The placement of the ram on the mainboard and the length of the channel to the ICH is designed to be a precise distance. Thus using your bios settings you tell the system, how long the signal will take to get to the ram, how long the ram will take to respond and how long to wait after a response is recived before sending the next one.

The actual distance the ram is placed from the ICH is goverened by the JDEC spec for that type of ram. This is so mainboard makers that support that ram are guaranteed that all the different brands made to that standard will work on their board.

If you set it up too fast, data is being sent while data is coming back and you get a collision. The result is that the system has to ask for the data again. This effectively slows down your ram.

The result of this is known as a memory bottleneck.

Since we know that sending data [signals] faster than the ram can process it causes the bottle neck, slowing everything down - i.e. telling the system to wait a little longer before sending more data - will effectively remove the bottleneck, hence the overall performance will be better.

The technique was taught to me by an intel engineer years ago when I was learning to configure servers.



DDR and SDRAM uses one channel from the ICH to the memory bank. Along this channel are 4 memory slots (in serial) and on older systems each slot equated to one physical stick of single sided ram.

On newer systems you have dual banked ram (otherwise known as dual sided). That is, there are ram chips on both sides of the ram sticks. In this case each side of the ram stick still applies to single memory slot, but you may only have two physcal holes to put the ram stick in.

An example would be my P4PE board. I have two sticks of 512Mb Kingston ram in physical slots 1 and 2. If I run Sisoft Sandra it tells me that I have 4 slots filled with 256mb ram.

The maximum performance of this type of ram is 3.2Gb/s which is well below the P4s data throughput of 4.2 Gb/s. Hence again you will suffer from memory bottlenecks when the CPU is going at full tilt.


Dual channel ram gives the higher performance because there are two memory channels running from the ICH to the ram instead of one for normal ram. One for each bank. This means the ICH can read from one channel at the same time as writing to the other. Thats why you need to install two sticks of ram of the same type. Think of it as RAID for ram.

In dual channel ram you still have 4 slots per channel lined up serially, but since you have two channels you have effectively two lots of 4 slots in parrallel.

Since you have two banks going in parralel, the maximum data throughput is 2 x 3.2Gb/s = 6.4Gb/s which is well above the maximum throughput of the P4 at 4.2Gb/s. Hence you will see some magazines stating that memory bottlenecks should be removed.

However, (and there is always one of those).. Intel are upping the frontside bus pretty soon to 800Mhz which is why using my slow-down technique above you will find DDR400 and DDR434 rated at CAS 3 rather than CAS 2.5 for DDR333 and CAS 2 for 133.

In any case, when overclocking ram, set the bios to the JDEC rating of the ram above that. So if you want to get DDR333 to run as DDR400 as I do, then set you BIOS to the JDEC DDR400 settings. Then bump up the FSB.

Method
28-03-2003, 08:02 PM
Tiggerz thanks for that, never knew something like that can happen and it makes perfect sense.

I have pc2700 ram, doubble sided. I run my whole sys at 166 fsb and was wondering what timings i should run my ram? You mention with ddr400 ram cas 3 is the best cas latency to use. What would ddr333 rams be?

Wibber
28-03-2003, 08:53 PM
the mem controller knows what the latency is set to and transmit accordingly, the only danger is if either end doesn't have the data ready to be transmitted in time (usually the mem), then it has to wait, effectively doubling the latency.
if you get a decrese in performance from lowering the latency, then this is whats happening, but in most cases the performance will increase, even with ddr400 at cas 2, though It'd be lucky to run that fast but I dont discount the possiblity

and yes :p its not JEDEC standard

Tiggerz
28-03-2003, 08:59 PM
Well, I run mine (DDR333) at CAS2.5 2-2-7 with 2.5v for bog standard setting.

I can get it to DDR400 and a bit by going CAS 2.5 2-2-8 2.7v and upping the FSB to 23x154.. Which gives me a 411Mhz Memory bus. This gives me a Sisoft benchmark of 3071 (compared to DDR400 2900).

I dont have a CAS 3 setting on my board as it only supports DDR333..

Right try the following (was reading the spec).

For DDR400 try using 2.66V CAS 3.0 3-3
or CAS 2.5 4-4

Note that CAS 3 has a lower maximum cycle time than CAS 2.5.

The last figure you will have to play around with as I couldnt find the recharge time. Its all in ns and I cant be bothered working it out.

For DDR333 (and DDR266) try using CAS 2.5 or CAS 2.0 - not sure of the other settings as I cant find the spec for that. See my defaults above.

Its actually JEDEC standard but I always refer to it as JDEC dont know why :)

The big problem I am having at the moment is my hard disk produces data errors when I ram up passed 3.6Ghz. Only does this for 3dmark03.. Everything else works fine.

Ragnor
28-03-2003, 09:05 PM
Was CAS 2 ever recommended by JEDEC..? Isn't PC2100 CAS 2.5 by default / JEDEC standard..

See here hans proves at least on an Abit KR7 KT266a the benefits of low cas vs FSB http://www.overclockers.co.nz/ocnz/misc/ddrguide/7.shtml

I'm not saying CAS 2 is going to be better or worse for dual channel DDR 400 boards... everyone is just going to have to test it for themselves in various benchmarks..

It's probably going to vary depending on design / manufacturer / model

Wibber
28-03-2003, 09:38 PM
pc21700 was cas 2 @ 2100, but 2100 was supposed to run @ 2.5

Tiggerz
28-03-2003, 10:13 PM
Each memory technology has a high and low setting (for timings).

DDR400 has the low timings at CAS 3 and high timings at CAS 2.5, DDR333 is 2.5 (low) and 2.0 (high).

DDR333 uses the same settings as PC2100 and the same technology.

Cabal
29-03-2003, 02:30 PM
So the thousands of people who buy super expensive low latency cosair DDR RAM are just wasting their money?

We should all be buying no name cheap ass slow ram instead?

Doesn't make sense to me.

mird-OC
29-03-2003, 03:05 PM
nah that's not really the case Cabal. Tiggerz is just overstating the fact that it's a possibility that RAM running at a speed faster than what the CPU is capable of handling will result in increased latency and therefore decreased performance.

it's only really only an issue with people running ultra fast RAM asynchronously to the FSB, like a lot of the guys running P4s... for instance a 400MHz FSB P4 running DDR400 (this isn't such a problem if you've got a good OC'er that allows you to ramp the FSB up nice and high tho).

a similar situation has struck the athlon/duron world with DDR333 and DDR400 mobos that offer asynchronous memory. the EV6 memory bus of an athlon/duron is double pumped, pretty much perfectly matching DDR SDRAM MHz for MHz. and as you'll probably know if you try running DDR333 at 166MHz (333) asynchronously on a 133MHz (266) FSB on an athlon system it will actually perform worse than if run at 133/133.

it's just a matter of keeping your FSB and RAM at speeds which compliment each other... on a athlon system this is easy to do since there is no multiplier lock so you can just set your FSB arbitrarily and keep the RAM in sync.

_N_
29-03-2003, 03:22 PM
has anyone seen this?

http://www17.tomshardware.com/mainboard/20020507/index.html

Tiggerz
29-03-2003, 04:24 PM
Originally posted by Cabal
So the thousands of people who buy super expensive low latency cosair DDR RAM are just wasting their money?

We should all be buying no name cheap ass slow ram instead?

Doesn't make sense to me.

No not really, there are other things you pay for as well. This is one of the reasons I always buy kingston.

Back during the clone wars (clones vs IBM PC not star-wars), we used to test machines for 100% compatability using a special piece of expensive diagnostic software known as Pinball. (no kidding here - being serious).

In order to build a 100% compatible clone for sale to the business markets, certain vendors had to achive very high level of manufacturing quality and relibality as well as a provide a consistant level of performance. All of this costs the manufacturer a heck of a lot of money, which is passed on to the consumer..

Now-days, as well as looking at the quality of the product we also review the history of the company over a 10 year period when determining product quality and performance.

In the case of kingston, I know that I will get a lifetime warantee on their product, and that it has been tested against all the mainboards that I am likely to use and will deliver a guaranteed level of performance. I also know that Kingston supply memory to many corporates and therefore have passed the vetting process.

Also, I know that in order to meet this high level of quality, the manufacturer has to effectively over engineer their product. Its this trade off on price that people who buy the more expensive stuff are going for.. In effect we know that the few extra dollars we pay for our product means that we are more likely to get extended performance out of it or at the very least, a known minimum level of quality. More so than if we go for a no-name brand which in effect is just a big gamble as to whether it will even work to spec, let alone exceed its performance criteria.

However, as the Toms hardware article mentioned, you also need to balance this with the other componants in the system. Thats the fun of system design.

Method
29-03-2003, 09:26 PM
Cabal also uber ram will pull off a uber overclock which will give you much more of a boost than timings. If you dont plan to fsb overclock a cheep stick with a lifetime warrenty is the best option.