Renamed: Should I use multiplier or increase FSB for faster RAM?

[The___Don]

I know faster is always better, but in my system, I have a multiplier unlocked qx9770 and Asus P5E64 WS evo motherboard.

Currently it has 2x1GB 1600MHz sticks.

I am trying to decide which ram to buy.

Will there be any benefit to buying 2000MHz which the board supports but considers a multiplier overclock?

I don't plan on oc'ing the fsb as I have full control of CPU speeds.

I want to get 2x2GB set, would I have to dump the old ram? Or can I leave them in and have the faster 2000 rated ram?

I am new to OC'ing, I think I have seen a ram frequency multiplier, is that doing essentially the same as the CPU multiplier? Does it have much effect?

[scaryjim]

PC1600? are you sure? That would be DDR-200!

Looking at your motherboard details I assume you're using DDR3-1600 (which is technically PC3-12800 in PC numbering ).

Your motherboard will support up to 2000 MHz DDR3 out of the box by setting the RAM frequency Mutliplier to the appropriate value (it does a similar job as the CPU mutliplier but for the memory). But tbh I don't think you'll see any noticable real world difference between just buying another 2 sticks of 1600MHz DDR3 and swapping for all 2000MHz RAM.

If you add 2000MHz RAM to your existing RAM you will need to run it all at 1600MHz otherwise you risk damaging your existing RAM - RAM tends to be a lot less forgiving about being overclocked than CPUs are!

Another thing to think about is cost: 1600MHz DDR3 is practically mainstream, whereas 2000MHz is very specialist, so it should be a lot cheaper to buy 1600MHz RAM.

If you're using a 64bit OS, you could always get 2x2GB DDR3-1600 to go with your 2x1GB giving you 6GB RAM total. For instance, this 4GB Corsair kit is pretty good value @ £55...

[The___Don]

PC1600? are you sure? That would be DDR-200!

Looking at your motherboard details I assume you're using DDR3-1600 (which is technically PC3-12800 in PC numbering ).

Your motherboard will support up to 2000 MHz DDR3 out of the box by setting the RAM frequency Mutliplier to the appropriate value (it does a similar job as the CPU mutliplier but for the memory). But tbh I don't think you'll see any noticable real world difference between just buying another 2 sticks of 1600MHz DDR3 and swapping for all 2000MHz RAM.

If you add 2000MHz RAM to your existing RAM you will need to run it all at 1600MHz otherwise you risk damaging your existing RAM - RAM tends to be a lot less forgiving about being overclocked than CPUs are!

Another thing to think about is cost: 1600MHz DDR3 is practically mainstream, whereas 2000MHz is very specialist, so it should be a lot cheaper to buy 1600MHz RAM.

If you're using a 64bit OS, you could always get 2x2GB DDR3-1600 to go with your 2x1GB giving you 6GB RAM total. For instance, this 4GB Corsair kit is pretty good value @ £55...

Thanks Scary Jim, I ashamedly mixed up my terminology, I always try hard to get he details correct.

You not so scary boy!

ok, so it's pretty flexible as long as keep the speeds ot the lowest rated, which is kinda obvious.

I think i might buy a good set of 2x2GB ram and then another whenthe time comes.

At the moment, the current 2 fairs really well anyway! So i think maybe no hurry

[scaryjim]

Yeah, for basic usage 2GB is plenty (I still use a 1GB laptop at work for email, web and office tasks, and it's pretty damn nippy!). There are very few tasks where you need masses of physical ram (sorting large data files in SPSS is one example!). As I said, if you're on 1600MHz already and you're using a 64bit OS so you can address more than 4GB of RAM, a 4GB kit of 1600MHz should see you right for the foreseeable future!

[Pob255]

However as this is a socket 775 motherboard there's very little advantage to having memory that runs that fast, increasing the FSB will have a far bigger effect than putting in faster memory because the memory is controlled by the northbridge which is running at the FSB speed.

Now DDR2 and DDR3 listed speed is twice the actual speed, the QX9770 has a listed FSB of 1600mhz however it's "quad pumped" ie listed as four times the actual fsb so you actual FSB is only 400mhz
So the upshot of this is if you've got you system at stock your QX9770 is running at 400mhz (x8 multiplier = 3.2ghz) with a raito of 1:1 on the RAM, then the ram would only be running at 800mhz (ie all that would be needed is ddr2 pc2-6400) now what you are probably doing is running the ram at a 1:2 ratio to make it 400 x2(ratio) x2 (DDR2orDDR3) = 1600mhz

This doesn't mean the cpu can actually send/receive data from the ram any faster because the northbridge that passes the data to and from the ram to the cpu is still only running at 400mhz
You will get very slight improvements in performance because the northbridge has to wait slightly less time for a ram cycle to end before it can send the next instruction set to it.

Which is why if you ran the ram slower and increased the FSB speed you're actually increasing the speed at which the northbridge can send and receive data from both the cpu and the ram.

This is the main reason DDR3 was never very popular on socket 775 motherboards, that and it was more expensive, now ddr3 has got cheaper it's now common on new 775 motherboards even though it's of little benefit.

[The___Don]

However as this is a socket 775 motherboard there's very little advantage to having memory that runs that fast, increasing the FSB will have a far bigger effect than putting in faster memory because the memory is controlled by the northbridge which is running at the FSB speed.

Now DDR2 and DDR3 listed speed is twice the actual speed, the QX9770 has a listed FSB of 1600mhz however it's "quad pumped" ie listed as four times the actual fsb so you actual FSB is only 400mhz
So the upshot of this is if you've got you system at stock your QX9770 is running at 400mhz (x8 multiplier = 3.2ghz) with a raito of 1:1 on the RAM, then the ram would only be running at 800mhz (ie all that would be needed is ddr2 pc2-6400) now what you are probably doing is running the ram at a 1:2 ratio to make it 400 x2(ratio) x2 (DDR2orDDR3) = 1600mhz

This doesn't mean the cpu can actually send/receive data from the ram any faster because the northbridge that passes the data to and from the ram to the cpu is still only running at 400mhz
You will get very slight improvements in performance because the northbridge has to wait slightly less time for a ram cycle to end before it can send the next instruction set to it.

Which is why if you ran the ram slower and increased the FSB speed you're actually increasing the speed at which the northbridge can send and receive data from both the cpu and the ram.

This is the main reason DDR3 was never very popular on socket 775 motherboards, that and it was more expensive, now ddr3 has got cheaper it's now common on new 775 motherboards even though it's of little benefit.

So I will be best to clock the FSB to push the RAM faster, otherwise the FSB is limiting the data access between the CPU and the RAM.

Then why do they have the extra multipliers for running the RAM faster. My board supports 1600 ('stock') 1800 and 2000 ratios.

Why do they add this if it is not actually helping?

I saw a review on xtremesystems.org (http://www.xtremesystems.org/forums/...d.php?t=187371) someone clocked the FSB upto 595MHz, getting the RAM to 2280MHz. In that review, he used Cellshock 1866 RAM Blue kit. Is it ok to run RAM so much over their rated speeds?

So I guess that if I put the multiplier down and then push the FSB it will be a faster system all around.

I am thinking of having the CPU at around 4GHz. At the moment it is at 3.6GHz with x9 multiplier.


A quick calculation I think i can run CPU at x8 with 500MHz FSB which should put me at 4GHz CPU and 2000MHz RAM.

If I do this, I assume i will need 2000MHz rated RAM.

[Pob255]

unfortunately overclocking is not quiet that easy

Have a read of clunk's excellent overclocking guide http://forums.hexus.net/hexus-hardwa...beginners.html

EDIT:Just downloaded the manual . . . Asus seems to have been able to both simplify and complicate it at the same time
Section 4.4.4
DDR3 frequency
auto
DDR3-667mhz
DDR3-800mhz
DDR3-835mhz
DDR3-887mhz
DDR3-1002mhz
DDR3-1066mhz
DDR3-1111mhz
DDR3-1333mhz
DDR3-1600mhz*
DDR3-1800mhz*
DDR3-2000mhz*

*when one of these settings is used the "FSB frequency and CPU Ratio Setting" will be optimized automatically
what exactly that will do if you try to overclock I'm not sure

Asus has also got a lot of settings you don't normally see in there as well as some of their own "Ai" settings eg Ai Clock Twister, which has 5settings or an auto mode, the manual says it ether "enhances" memory stability on low settings or "accelerates" performance on high settings, but no clue as to what it's actually doing.

All told this is a top end board which means you're going to have to do some research and spend quite a bit of time learning how this board works and how to get the most out of it.

[scaryjim]

TBH a 1600MHz FSB isn't going to be that much of a limiting factor. With Core 2s with a 266MHz base clock (i.e. 1066MHz FSB) pushing the FSB could get you a significant boost. Once you're already at a quad-pumped 1600MHz, the returns from pushing the FSB up are going to be less noticable.

If you do push the FSB up, you'll want to reduce the memory multiplier to keep it roughly within 1600MHz. Since the memory controller is (I assume, anyway) dual channel, you can actually saturate the FSB with memory running at half the quad pumped speed: i.e. a 1600MHz quad pumped FSB can be saturated by DDR2-800 memory. So you don't need to buy ultra-high-end memory to get a good overclock (in fact dual channel DDR3-1333 would do the job, pretty much) - you just need to play with the memory multipliers to get the best speed for your RAM modules.

As Pob says, read Clunk's overclocking guide, which is well written and beginner friendly, but remember that you have more options thanks to your high end board and unlocked CPU. Once you're confident with simple OCing from Clunk's guide you can start experimenting a bit more on your own.

[The___Don]

Ok, so what if I get 2x2Gb 2000MHz Ram, dump the current 1600MHz RAM
and clock the FSB to 500MHz from the core 400MHz?

That should give me my "quad pumped" (I hate that marketing term, it's really PSK, phase shift keying) frequency of 2000MHz and as such not saturate the FSB buffers to the CPU.

Is this reasoning sound?

[scaryjim]

tbh you can do that with your existing 1600MHz RAM.

The FSB width on a Core 2 is 64bits. The memory controller uses 2 64bits paths to the memory. So the FSB sends 4 64bit transfers per clock cycle to the memory controller, and the memory controller can send 2 lots of 2 64bit transfers to the memory per clock cycle - so it only needs to run the memory at half the "rated" / "quad-pumped" FSB. In other words (theoretically, at least) running the RAM at 1:1 with the actual FSB provides enough bandwidth to saturate the FSB. This means that if you run the FSB at 500MHz, your DDR3 speed is going to be 1000MHz, easily manageable by your DDR3-1600. So you can run something like a 2:3 multiplier (which would be DDR3-1200 at stock speeds) and still only have your 1600MHz RAM ticking along at 1500MHz: that will still provide half as much memory bandwidth on tap than the FSB can shift. With an FSB, the FSB is usually going to be the bottleneck.

[The___Don]

But isn't my FSB at 400MHz now, with the quad pumped at 1600MHz and the RAM is 1:1 and shows 1600MHz.

I was under the impression that clocking the FSB would increase the RAM to the same.

Otherwise, why do we buy 1600 MHz RAM if what you are saying is that my FSB is really running at 400MHz and the RAM is DDR so just 800MHz

According to that logic, no amount of overclocking will get the ram near it's limit as the FSB is the limiting factor.

[Pob255]

Yep that's basically it.

The intel listed CPU fsb is the thing that's "quad pumped" by the marketing department to make it sound faster than it actually is, the memory is only "double pumped"

if the motherboard is running at fsb 400mhz and a cpu:memory raito of 1:1 then your memory is running at 800mhz not 1600mhz

However you motherboard manual mentions automatic optermisation when set to DDR3 1600mhz, there's also XMP, if your memory has it.
So what's happening currently is that one of these settings is automatically adjusting your ratio to get the memory as close to 1600mhz as possible, in your current case it should be 1:2

EDIT:As to why we buy ddr3 1600mhz ram, we didn't not for 775 systems anyway, however with AMD and the new core I intel cpu's it's changed, the memory controller in now on the cpu, which removes the northbridge memory controller bottle neck and gives memory speed a far larger influence on both performance and overclocks.

[scaryjim]

But isn't my FSB at 400MHz now, with the quad pumped at 1600MHz and the RAM is 1:1 and shows 1600MHz.

As Pob says, somewhere in the depth of your BIOS there is a setting which is running the RAM @ a 2:1 ratio to the FSB, so it's actually being driven at 800MHz (== 1600MHz DDR). If you can find it you should see options to run the memory at lower speeds right down to 400MHz actual (800MHz DDR). When you do FSB overclocking it's very important to turn the memory multiplier down as memory tends to overclock a lot less than CPUs, so if you leave your memory multiplier high it will limit your overall overclock.

Remember (as Pob also said) that socket 775 CPUs don't access the memory directly - they comunicate with the memory controller in the northbridge via the FSB, and the memory controller sends those requests on to the memory. It can do that at a different speed to the FSB. So, for instance, my Q6600 has a 266MHz (or 1066MHz, as Intel would say...) FSB, but my memory runs at 400MHz (DDR2-800). What you're looking for is to push the FSB as high as possible with a 1:1 memory ratio, then to adjust the ratio to get as close to 1600MHz as possible without going over.

[The___Don]

Sounds good.

I have been reading through a long thread about people overclocking the FSB on my board over at xtremesystems.org forum and the highest people reach (with watercooling) is 600MHz.

I'm only on air, but have good cooling in my case with 4 120mm fans over the entire MB area.

So if I set the RAM multiplier 1:1 then any FSB overclocking will not be limited by RAM.

What about getting 2000MHz RAM if I push it up to 500FSB?

I assume I and run that at 2:1 multiplier as it currently is.

[scaryjim]

Well, theoretically I guess so, but as we've said it won't actually increase the memory bandwidth available to your computer so it really isn't worth the extra expense. A 4GB dual channel kit of DDR3-2000 is £20 - or to put it another way 36% - more expensive than an equivalent DDR3-1600 kit - and you won't see any real world benefit from it. Better off saving the money, IMNSHO.

[Pob255]

More to the point you could get another pair of 2x1gb ddr3 1600mhz for around £30 http://www.ebuyer.com/product/239265 which will give you 4gb total

600mhz fsb and a 1:1.33 ratio will give you 1600mhz memory speed.

Although remember overclocking is never guaranteed and just because one person can achieve the same overclock on the same model hardware does not me you will be able too.
Not all chips are the same and you are pushing them over the designed maximums.
I'm not saying don't do it, just don't stick it on 600mhz and expect it to work because someone else can.
Take it in stages, you can generally take bigger jumps early on, but as you approach the limit of the overclock you want to greatly reduce the increases.
Once you have found the limit you'll then want to move it back a bit for day to day running for safety.