ram question!

[LovEnPeaCE]

could any of you explain to me the point of having a higher speed ram than pc3200(ddr400) on a motherboard that says it supports DDR266/333/400?

[Scintilla]

<i>Is</i> there one?

[Miz Ducky]

The ASUS "P5GDC-V Deluxe" has 2x DIMM Dual Channel DDR2 400/533 4x DIMM Dual Channel DDR 400/333 Max 4GB.

As I have been shopping I've come across several things like this that have made me curious too.

But, won't the mobo only accept the type of memory that is listed.

Would it even work if you have a DDR2 533 stick in a DDR 400 slot?
I'm no expert by any means, but I'm thinking No.

[Zero1]

Basically it's for overclocking.

I had an XP2600 a while ago, (runs default at 2075MHz (12.5 x 166) and have had a few DDR400 motherboards, and having faster RAM will allow you to run the memory 1:1 with the FSB, when you clock it past 200MHz, otherwise you have to set a divider in the BIOS.

For instance, my old Epox 8RGA+ motherboard has done 222MHz FSB before (probably capable of more, but the CPU was designed for 166MHz, so it's a pretty awesome increase).

If I had PC3200 RAM, it might not have been a good overclocker, so I would have had to use a divider, the smallest ratio was 5:4 I think, so the RAM would have been running at 178MHz. Obviously here you are losing memory performance to run a higher clock speed, which isn't ideal.

I had some Kingston PC3500 (Ok not a lot faster, but anyway...) which is rated for 217MHz, so in this instance you could have run it at 217MHz FSB safely without having to use the divider, (which would have caused the RAM to run at 178MHz), as you can see, you are then getting a big difference between 178 and 217, and it means you aren't "throwing away" performance by using the divider.

Luckilly for me, the Kingston was able to run at 222MHz no problem, if I got some faster RAM, I may have been able to hit higher FSBs, but I think I was pretty much pushing it.


Well thats a relatively small performance boost 200 > 222 MHz, but it could have added a theoretical 275MHz to my clock speed. (It actually gave me 242MHz since I was using an x11 multiplier, and the CPU maxed out at 2500MHz).





Just recently I moved to Athlon64, tried the Epox 8KDA3+ motherboard, but it appears the chipset and/or something else is buggy as hell, so I'll be getting the new DFI lanparty board when it's available over here.

It's been tested to 308MHz FSB, which is kickass for a 200MHz rated board (again it's rated as DDR400 (which is actually 200MHz DDR)) and currently as far as I'm aware, the fastest DDR1 RAM you can get off the shelf is approx 275MHz, as you can see, a divider would be needed (unless you overclock the RAM), but the board reaches 270MHz if you are using 2 sticks, so PC4400 is ideal if you are going to use 2 sticks in this board.

Anandtech Said:

The performance at lower ratios, on the other hand, took our memory to performance levels never reached on any board - AMD or Intel. Both the Geil and OCZ memories are based on very recent Samsung TCCD memory chips, which performed well in our recent memory tests on an Intel test bed. They topped out at DDR557 to 561 on the Intel, so I was skeptical when DFI told me that TCCD memory could reach DDR600 on the nF3-250Gb. With a little tweaking, we were able to reach even further with this same memory, to DDR616 at 3-3-4-10 memory timings at 2.8V memory voltage.

On CZ PC3200 EL Platinum Rev. 2 or Geil PC3200 Ultra X



Of course if you just want a computer that works, and don't plan to run components out of spec, go for the PC3200

[Miz Ducky]

You entirely lost me when you started mentioning dividers, multipliers and ratios.

Since you just went through a major upgrade to the Athalon 64, why do you still have a 200 MHz motherboard?
I think I'm missing something.

[madmag9999]

yea Z3r01 you lost me a little bit with the divider thing. maybe i know what it is just not useing that term becouse i have been ocing systems for a long time. but mainly what Z3r01 said is that u can oc the ram to go faster then what its rated by setting the mhz and multiplyer higher. and miz ducky a fsb of 200mhz isnt bad becouse u have the multiplyer to worry about to.

[Zero1]

You entirely lost me when you started mentioning dividers, multipliers and ratios

Don't worry about dividers unless you are overclocking, or attempting to run the FSB faster than it should. A divider is a setting in the BIOS that sets the memory to run at a designated fraction of the FSB speed. For instance setting 5:4 will make the RAM run at 4/5ths the speed of the FSB.

So if the FSB is running at 200MHz (but this is dependant on your processor, some older ones run at 166 or 100) the RAM will run at 166MHz. Then when you increase the FSB speed, the RAM speed rises synchronously.

Therefore if the FSB is then set to 250MHz, the RAM will then be running at 200MHz. How does this work? Well the divider 5:4 can be divided (of course!) to give us a decimal value.

5/4 = 1.25

Now you can use that decimal to figure out the RAM speed, or the FSB speed as long as you know one or the other,

To find the RAM speed:
If you know the FSB=250 and want to know what the memory would run att
FSB / (Divider as x/y) = Memory speed in MHz (*2 for the DDR Rating or *16 for approx PC rating)
where x=Numerator and y=Denominator

So when we fill the values in:

250 / (5/4) = 200 (* 2 = 400 DDR or *16 = PC3200)

Since you just went through a major upgrade to the Athalon 64, why do you still have a 200 MHz motherboard?

My bad. Athlon 64 motherboards work differently from the older Athlon boards. The old Athlon (Socket A) typically ran at 133, 166 or 200 FSB. This still runs a 200MHz FSB (due to the FSB being a deciding factor in the speed of the PCI/AGP bus, Memory bus, CPU speed setting etc), but uses a multiplier to give a larger final FSB speed of 2x800 - 2x1000MHz.

Basically if they just had a 1600MHz FSB in the beginning instead of a 200MHz one with a 4x + 2x multiplier, things would have gotten complicated. CPU speeds are generated like this:

CPU*FSB=CPU Speed in MHz

So for me its 11x200=2200MHz

If it was a 2x800MHz FSB from the start, it would be extremely difficult to set accurate CPU speeds. You would probably need CPU multipliers accurate to 3 or 4 decimal places, IE 2.75 x 800 = 2200MHz

Also, as I mentioned before, the FSB affects the RAM speed. So to have the RAM run at 200MHz (don't forget, this board doesn't use the new DDR2 RAM) you would need crazy dividers like 8:2.
The whole thing would get pretty messy, and would be a pain in the ass for calculating variables for overclocking and such.

Much the same way as the CPU speed is generated, the FSB speed is now generated in a similar way.

LDT*FSB=HTT
So for this instance it's 4*200 = 800 (Hypertransport is two way, so you may see it referred to as 800MHz or 1600MHz, just like 200MHz RAM is called 400MHz DDR).


In short, No, my motherboard isn't running 200MHz, it's actually 800MHz (or 1600MHz, which is made from the 200MHz FSB and a 4x HTT Multiplier) and just to confuse things, I had it running at 944MHz (1888) when overclocked.

yea Z3r01 you lost me a little bit with the divider thing. maybe i know what it is just not useing that term becouse i have been ocing systems for a long time.

OC'ing gives you a certian satisfaction doesn't it? 8) I don't think I'd ever own a system again and have it just running at it's factory speed.

As for the divider, it could be called a number of different things in the BIOS, could be something like RAM to FSB ratio or simply RAM speed (I think my old board used to let you specify the RAM speed in MHz, as opposed to setting a divider, not sure though, fried that processor).

I'm ditching my Epox8KDA3+ though now and going for a DFI Lanparty UT nF3 250Gb if I continue to hear good comments.

There's a nice review of it here at Anandtech

Check it out, there's some articles that may help you out, there are quite a few BIOS screenshots too.


Well I hope I didn't confuse things too much

[Miz Ducky]

Thank you so much for that detailed explanation. It really helped. No one has ever told me all that before. Of course, I'm not so "power/speed hungry" that I've ever tried to oc, or ever wanted to either. But now when I see this stuff I'll understand it a lot more than I would have previously.

Maybe I'll just start PMing you with all my questions.

[Zero]

I had an XP2600 a while ago, (runs default at 2075MHz (12.5 x 166)

I don't mean to be picky, but how do you run half a processor at default?

-Zero

[Zero1]

I had an XP2600 a while ago, (runs default at 2075MHz (12.5 x 166)

I don't mean to be picky, but how do you run half a processor at default?

-Zero

It's not, it's a thoroughbred core, which run at 166MHz (333FSB), the Barton cores run at 200MHz (400MHz) (albeit with a lower multiplier)

Also I dunno whether you accounted for it or not, but AMD processors since the Duron and original Athlon always run slower than rated (because they are more efficient than Pentiums etc.)

But back to the FSB speed (I assume that's what you meant was running half speed), if you mean by half speed that it should be running at 333MHz, it sort of is.

You see there are 2 ways of measuring FSB speed, and 3 ways or measuring RAM speed.

Since I've already covered RAM, I'l use it as an example.

I've got some 217MHz RAM, which is termed as DDR434 or PC3500.
As you can see, the DDR rating is double the clock rating, this is because the RAM does 2 instructions per second, one on the rising, and one on the falling edge of the signal (IIRC). Therefore 217MHz RAM, can be rated as DDR434, both terms are common, and it's important to take note of which one is being referred to what with DDR2 now.
The PC3500 number is Bandwith in MB/s Ie this particular RAM, when set at 217MHz, will theoretically shift 3500MB of data per second under ideal conditions.
The PC number is approx (RAM speed in MHz) x 16 = PC rating
Or if you are working from the DDR number, which is double the RAM MHz, it's x8.


FSB speeds are typically referred to in a similar way. For instance as I stated before my old motherboard's FSB was 166MHz at default (which is sometimes termed as 333MHz FSB (Just a bit of marketing guff to make it sound more impressive). So where does the 333FSB come into it? It's probably just the manufacturers reffering to its theoretical throughput, ie as in both channels being used at once. (I'm assuming the FSB works on a full duplex basis, and is 166MHz each way)

The reason I refer to the FSB in it's MHz speed is because it's how the clock speed is generated for example 12.5 x 166 = 2075 MHz, with a total FSB throughput (and/or memory dependant if it runs synchronous with the FSB or uses a divider) of 333MHz

In short, 166MHz is it's "physical" speed and 333MHz is it's "effective speed).
It's just like me saying that my Athlon 64 runs 200MHz FSB stock (which it does), but is advertised as 800MHz FSB or 1600MHz HT. In this case it uses a multiplier for the FSB of 200x4 to give 800MHz, the 1600MHz is it's effective speed, so the Athlon64's 800/1600, is similar in principle to the Athlon XP's 166/333 and the Barton Core's 200/400




Probably confused things ten fold, but in short, the CPU and motherboard were running at their stock, advertised speeds no problem. I was able to raise the FSB from 166(333) to 222(444) with the RAM using a 1:1 ratio, so it was running in sync with the FSB.


I've had a comuter for 3 years now, there's no way I'll let my systems underperform what they are rated for, heck I push them to the edge, even killed 2 motherboards and a CPU doing it, not smart, but you live and learn. I may have said it before, but I don't think I'll ever own a computer that runs at factory speeds, it's gotta be pushed that little bit further.