Ok could someone please clear this up....

[mac404]

Pretty much everyone has been stating 1ghz DDR2 ram for the GeForceFX, however exactly how they come up with this number is harder to come by. Before you start to moan about another NV30 thread (I know, I'm probably too late ), I only have one question: What exactly does the 1ghz DDR2 spec entail? I mean, is it running at 500mhz, or 250mhz? I've heard both, so I'm getting very confused. Any clarification you guys have would be very helpful.

-mac404

You only die once, don't mess it up.

 

[phial]

if DEFINATELY runs at 500mhz. ive read this from numerous sources. DDR2 still runs at double the clock speed effectively, but it allows higher speeds than standard DDR and its supposed to allow twice as much data to be passes per clock compared to DDR, or 4 times as much per clock compared to SDR. thats what they say

 

[andyk]

I too have been greatly confused by all this talk about DDR2 and I wonder why none of the hardware sites have written an article about new memory technologies in general.
However in the anandtech preview of the GFFX he states that nvidia doesn't use real DDR2 on the card. Only some of the characteristics from the JEDEC specification are used. He then writes that this type of memory does not transfer 4 times per clock but only twice, which could imply that the JEDEC specification calls for 4 transfers per clock. Also there is no such thing as real DDR2 for graphics cards because no official specification exists.

The answer to your question: The ram on GFFX runs at 500 Mhz!

Many people will disagree with real DDR2 transfering 4 times per clock - they will say that that's what QDR is for. I really am not sure about DDR2 specs but I'll look into it if I can get my hands and the JEDEC DDR2 spec.

By the way, if the memory transferred 4 times per clock it would have an effective speed of 2000Mhz just like the QDR technology used in the P4 FSB.

Regards
Andreas


<P ID="edit"><FONT SIZE=-1><EM>Edited by AndyK on 11/30/02 01:12 PM.</EM></FONT></P>

 

[mac404]

Thank you. I was pretty sure it ran at 500mhz as well, however a site or two were saying some other things that got me confused. That could make sense that it's not completely the DDR2 spec. From the memory section of this board:
"DDR2 is the next generation DDR memory that uses a quad pumped data bus as opposed to the dual pumped data bus for ordinary DDR."
And some bandwith from the "preliminary JEDEC spec":
As part of the preliminary spec, JEDEC approved 400 and 533MHz DDR chips. Comparable DDR memory modules would carry the PC3200 nomenclature for a 3.2Gbyte/s bandwidth using the 400MHz chip, and PC4300, with a bandwidth of 4.3GBytes/s for the 533MHz chip.
If anyone wants to figure that out (I am too tired to think very clearly), go ahead.


You only die once, don't mess it up.

 

[mac404]

Just was wondering, then: if it "still runs at double the clock speed effectively", then why would it also allow "twice as much data to be passed per clock compared to DDR"?

I just want to try to get this unraveled as much as possible.

You only die once, don't mess it up.

 

[eden]

DDR is the same speed as SDR RAM, however it transfers twice more data per clock, therefore many would go claim it runs at twice the speed. That's not true!
You cannot pump a CLOCK speed like this, as far as I am concerned only CPU multipliers can do that.
DDR 2 is in reality supposed to be transfering FOUR times more data per clock, so that if SDRAM ran at 133MHZ, a same clocked DDR 2 chip would be claimed to run at 533MHZ, while not true but has the power of what 533MHZ transfers.
So DDR2 transfers four times more bandwidth than SDR.
DDR2 also comes with advanced electronical specifications to allow clock speed ramping. Therefore while DDR is currently having problems at 200MHZ (400MHZ DDR effective), DDR2 will have no problem scaling beyond to like 400MHZ (800MHZ DDR), AND will double the bandwidth DDR offers.
So, currently DDR400 gives you 3.2GB/sec, DDR2 will give you 6.4GB/sec, and can scale more easily like a process shrink on microprocessors.

Unfortunatly nVidia did something that screws us all in the understanding of DDR2. It seems their claimed DDR2 chips are not quad pumping the data but still same transfer as DDR, simply with better clock scaling. Why on earth did they not opt for the real DDR2 and have 32GB/sec of bandwidth is beyond me. Some companies just don't try to go further.

--
*You can do anything you set your mind to man. -Eminem

 

[phial]

i just made a thread to clear this up.... read =)

 

[mac404]

That was very helpful. I've also been reading various articles (including a PDF about DDR2, interestingly enough, written by the JEDEC from ATI). The consensus on this was a data prefetch of 4 and a of a module running at 1/4 the bus frequency which is inline with what you said (and what I always thought). Seems like nVidia is screwing with us once again. Thanks for the help.

You only die once, don't mess it up.

 

[eden]

a module running at 1/4 the bus frequency

That I don't get. Wouldn't it mean run at an "effective" 4/1 frequency albeit not actually 4 times higher?

--
**Canadian joke:
Here we don't say the word "retarded", we say "Alliance"! -Mike Bullard**

 

[mac404]

It means the actual module of DDR2 would be running at 133mhz to support the bandwith of a 533mhz FSB (as it runs QDR for an "effective" 533mhz) if I'm not mistaken. Supposedly offers the same bandwith, but I don't know if it actually does. Any other comments?

You only die once, don't mess it up.

 

[eden]

Yup that's the gist of it. I was just looking at it inversly.

--
**Canadian joke:
Here we don't say the word "retarded", we say "Alliance"! -Mike Bullard**