RDRAM vs DDR

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scrumlord

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Oct 29, 2002
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OK, I know the subject has probably been beat to death. I know Intel doesn't look to be moving forward on Rambus. I know Rambus have acted like jerks businesswise. I even know Yellowstone is imaginary at the moment, BUT from a technology view what is faster DDR or RDRAM (at premium speeds, ie dual DDRII-433 vs PC1066)?

According to reviews, both are nearly the same in speed, but it seems illogical given clock speed differences and it seems like RDRAM technology is more efficient (latency, error cycles, etc) at 16/32 versus 64/128/256 bit. Non-ECC please.

Real world speed, what is people's opinion on which is better - DDR or RDRAM technology?
 
I say dual channel DDR is the best option right now as far as performance.

<b>Just because I like AMD or Intel more at a time because of one product compared to another, does not make me a fan boy, it makes me a person who is able to make a descision for myself.</b>
 
RDRAM and DDR SDRAM have the same bandwidth (PC1066 has the same bandwidth as PC2100). Now before you fly off the handle, remember that on the P4, Rambus is mounted in pairs.

Why then aren't dual channel DDR boards with the i845PE/GE chipsets performaning as well as i850E boards? Intel probably did that intentionally.

<font color=blue>You're posting in a forum with class. It may be third class, but it's still class!</font color=blue>
 
The reason DDR and RDRAM seem to be on par speed wise is because of the following reasons.
The P4 is a slow processor by design but it needs a lot of memory transfer rate to try and compensate. Now RDRAM is a slow memory by design but it is good at providing a lot of memory transfer rate but at high latency. So what you have is the latency of the RDRAM and the latency of the CPU work together and it turns out to work ok. But if you took RDRAM over to an AMD platform for example you would KILL the performance of the AMD CPU because RDRAM is too slow to be any use to the AMD CPU and you would have the CPU sitting there forever just waiting on the memory to send its data. DDR Ram might not be able to transfer as much in a clock cycle as RDRAM but it responds a massively amount faster which suits AMD better because AMD is by nature a faster CPU than the P4 will ever be. That is why AMD is a faster platform overall because the majority of applications it is the response time of the system that matters and not the amount it can carry. And the reason DDR doesnt help a P4 is because the P4 CPU is not fast enough to send enough seperate request to the DDR Ram so the ram is sitting there the majority of the time just waiting for the CPU to catch up to the RAM. According to memory the CAS Latency on top of the line RDRAM is something like 32 (yes thirty two) and the CAS Latency of avarage cheap DDR is 2.5 (two point five). If you can translate this into english then there is your answer to why RDRAM is better for a P4.
AREA_51
 
Once again, vk2 you have no clue. Stop trolling Intel posts as the crap you spew is useless information.

"The P4 is a slow processor by design"

"AMD is by nature a faster CPU than the P4 will ever be."

AMD troll, you gotta do more research it seems. Lets take the oldest RDR PC800-45 for example. it runs at 45ns and up to 411Mhz @ <b>cas 2</b>, over 411Mhz it drops to cas 2.5. WTF you got cas 32 is anyones guess (most likely smoking crack).

Do yourself a favor and not respond to Intel posts as you are stupid.

You are limited to what your mind can perceive.
 
Ok, proof for you.

<A HREF="http://fugger.netfirms.com/800-45best.jpg" target="_new">Sandra SS of RDR PC800-45</A> info from the SPD.

You are limited to what your mind can perceive.
 
I dont understand why you feel so threatened by me. It is unjustified. And the P4 IS a slow processor by deisgn. It is because of the stupidly LONG pipline. And AMD is a faster chip than the P4. The short pipeline is the reason. It was a bad choice of words on my part. I should have said "AMD is by nature faster than a P4 at same clock speeds." or something else simelar. And I dont know where you get this 411Mhz crap on RDRAM. PC800 Runs at 100Mhz. Though if you managed to overclock your FSB by 300Mhz I would love to know how. But seriously the bus for PC800 is 100Mhz NOT 400mhz and CAS 32 IS TRUE. I have read it in MORE THAN ONE place while trawling the net. That is BASIC computing 101. I dont understand where you get the cas 2.5 for RDRAM. It is just not possible for RDRAM to do that. It is designed for large transfers NOT fast response. Once again I urge you to stop making yoursllf looking stupid and quit before I run over you again. Those tire marks all over you now already look nasty enough without adding even more.
AREA_51
 
The SPD (serial presence detect) is a chip on the ram that is programmed with spec of the ram.

The P4 has quad pumped FSB so if the FSB is at 100Mhz the RAM is at 400Mhz.

In the SS I posted it shows clearly the PC800-45 is rated @ cas 2 up to 411Mhz and when it breaches 411Mhz it will drop to cas 2.5 This is a known fact, nothing I made up on the fly. I posted the SS to remove any doubt of the cas latency that RDR operates at.

Sadly you have read wrong or misunderstood.

You have a lot to learn about bandwith.

You are limited to what your mind can perceive.
 
I know its quad pumped. But it doesnt make it 400Mhz. It is still 100Mhz. That is my point. And maybe there is a slight chance I am wrong on the RD CAS. But I have read it in more than one place so I dont think so. But I will leave that one alone because I am not as versed as I really should be when it comes to ram.
AREA_51
 
The ram does run at 400Mhz (PC800) Cas 2

You might be confused with 32 split bank architecture or PC1066-32ns

You are limited to what your mind can perceive.
 
I agreee wtih Fugger. Vk2 you have no clue. P4 is design to be manufactured at much higher clock speed than Athlon. I know a 3 GHz Athlon will be faster than 3 GHz P4 but AMD still not able to produce 3 GHz Athlon for market but 3 Ghz P4 is already availiable. Just want to make sure you know currently the fastest desktop PC for most application is base on P4.
 
It does NOT run at 400Mhz or even the PC1066 stuff doesnt run at 533Mhz either. It is 100 and 133mhz respectly quad pumped. The base frequency is still 100 and 133mhz. NOT 400 and 533Mhz. That is just a marketing ploy to inflate the figures and make it look better. DDR is gulty of the same they call it 333 and 400Mhz when it is only 166 and 200mhz. Oh and to the other guy umpec I think it was. I had stated that I had used the wrong wording. "The P4 is by nature a very ineffecient and slow chip and it uses massive clock speeds massive memory bandwidth to compensate." That would have been a better wording.
AREA_51

<P ID="edit"><FONT SIZE=-1><EM>Edited by vk2amv on 12/23/02 11:44 PM.</EM></FONT></P>
 
You should read more carefully before you reply. I agree P4 is slower than Athlon with the same clock speed. The problem is that P4 can be manufactured at much higher clock speed than Athlon with current manufacturing process. P4 is the fastest desktop platform because with current manufacturing process the fastest P4 have better performance than the fastest Athlon.
 
What is wrong with take the advantage of the massive memory bandwidth that is available? There no reason not to use the massive memory bandwidth that is available. P4 is more capable to use the memory bandwidth that is available than Athlon. I was very disappointed with the performance of nForce chipset because Athlon cannot even take the full advantage of the Dual channel DDR available with nForce.
 
Problem is in 99.9999% of applications it doesnt need or let along use that much memory bandwidth. It is just showing how weak the P4 is to need that bandwidth to try competing with an athlon at slower clock speed but more importantly WAY less memory bandwidth.
AREA_51
 
The extra memory bandwidth will help the performance of the computer. Since all the application have to be run from memory so all application will be benefit from it. As I said before P4 is designed to be manufactured at higher speed so it is not fair to compare P4 to Athlon at same clock speed.
 
In reply to

And the reason DDR doesnt help a P4 is because the P4 CPU is not fast enough to send enough seperate request to the DDR Ram so the ram is sitting there the majority of the time just waiting for the CPU to catch up to the RAM.


Where did you get the idea? You are totally wrong about it. You really should stop posting on something you do not understand.
Almost all CPU (Hammer is an exception since it has build in memory controller) access memory via chipset. CPUs do not communicate directly with RAM. CPUs access different kind of RAM in the same way by sending request to chipset.
 
You need to run the report wizard and run the memory tests, thats how I get memory module information from the free version.

You are limited to what your mind can perceive.
 
Carefull, he will start to call you ignorant or something else insulting when he doesnt get his way.

As we can see he does not understand what he is talking about even tho it must be true because he read it somewhere else.

You are limited to what your mind can perceive.
 
Hey you were the FIRST person to call anyone ignorant on the other thread. And that was because me and OTHER PEOPLE AS WELL PROVED YOU WRONG. Then you started calling US ignorant. You are just a pretty pathetic flamer that gets mad when you are proved wrong on anything. I suggest you change your dipers and maybe you wont have such a bad disposition to everyone who doesnt agree with you.
AREA_51
 
You forget the 20 stage pipeline on the P4. That causes long latencies on it while it waits on the pipeline. Also memopry bandwidth does NOT affect most programs in a real world enviroment unless it is severly constrained. Look at seti at home or office for an example. Do they need 5 or 6gigs per a second memory bandwidth. No they dont. They benefit more from lower latencies on the CPU and Memory. And I have to admit as much as it pains me that even with dual ddr 400 with nforce 2 you can still get higher memory bandwidth from top of the line RDRAM. (Dual module 1066 I think it was. Correct me if I am wrong on that one.) Though I think I will retire from this subject because as I said I dont know as much as I really should about memory.
AREA_51
 
The latencies is overcome by the high clock speed. That is why the fastest P4 platform is faster the fastest Athlon platform for almost all application.
 
In reply to:

And I have to admit as much as it pains me that even with dual ddr 400 with nforce 2 you can still get higher memory bandwidth from top of the line RDRAM. (Dual module 1066 I think it was. Correct me if I am wrong on that one.)

You are wrong again. You should really check the information before you post.

Dual Channel DDR at 400MHz have higher bandwidth than Dual channel RDRAM at 1066MHz.
 
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