Which is faster? DDR or RDRAM

[pball68]

I am trying to get the faster Ram out of these two types. Which is faster? I am looking either at DDR 3500 256k or RDRAM 1066MHZ 256K. Just trying to see which is faster. Can you go into depth too why one is faster than the other. I am a little confused on that also. Thanks in advance.

 

[xxsk8er101xx]

RDRAM PC1066 is faster.

<A HREF="http://www.anandtech.com/mysystemrig.html?id=9933" target="_new"> My Rig </A>

 

[pball68]

Is this because the RDRAM is 1066 MHZ and the DDR is 533 MHz? Trying to find out exactly.

 

[camieabz]

Yup.

<b><font color=blue>~ BIOS SETTINGS: Fast, Hot, Unstable...That ought to work. ~</font color=blue></b>

 

[pball68]

Ok, thx

 

[xxsk8er101xx]

no ... they are different technologies. You can't compare them. only in benchmarks can you compare.

<A HREF="http://www.anandtech.com/mysystemrig.html?id=9933" target="_new"> My Rig </A>

 

[xxsk8er101xx]

no the guy is wrong.

Has nothing to do with mhz and DDR's top rating is 400mhz and i believe that has yet to be approved by JEDEC. So the standard is 333mhz DDR.

But RDRAM and DDR are DIFFERENT technologies that you cannot compare. RDRAM uses serial technology and DDR uses parallel. Differen stuff completely.

so NO! Just because rdram is 1066mhz and ddr is 533 so rdram is faster is wrong! Considering there is NO 533mhz DDR RAM.

I suggest you do some research.

<A HREF="http://www.anandtech.com/mysystemrig.html?id=9933" target="_new"> My Rig </A><P ID="edit"><FONT SIZE=-1><EM>Edited by xxsk8er101xx on 07/29/02 02:01 PM.</EM></FONT></P>

 

[bum_jcrules]

400MHz is already a part of the DDRII standard. So Yes it is approved.

RDRAM is 533MHz. It uses a DDR signal and thus has an effective 1066MHz. But it actually has frequency changes at 1,600,000,000/3 cycles per second. (~533MHz)

So for actual signal speed they are the same. Electricity through copper is the same for both. RDRAM has more cycles per second than DDRSDRAM. DDRSDRAM has a wider bus and thus can have a wider bandwidth than RDRAM.

Then there is latency but I don;t ant to get into that...

Back to you.

<b>"If I melt dry ice in a bathtub, can I take a bath without getting wet?" - Steven Wright</b>

 

[xxsk8er101xx]

Thats DDRII not DDR. There's a difference i do believe. Or am i wrong? *shrugs*

<A HREF="http://www.anandtech.com/mysystemrig.html?id=9933" target="_new"> My Rig </A>

 

[Crashman]

OK, PC1066 has 4.2GB/s bandwidth. "PC3500" would have 3.5GB/s. I've never seen REAL PC3500, only some overclocked stuff that won't even run at full speed on most boards (because it requires up to 3v on the 2.5v line, which most boards won't supply).

So in reality, let's compare VIABLE memory solutions, DDR400 is PC3300/PC3200. 4.2GB/s v 3.1GB/s. Now you see why RDRAM is "faster".

Plus, the most common PC1066 RDRAM is Kingston 32ns, which happens to be a cycle time rated for 600MHz operation (PC1200 RDRAM). So it can be overclocked by 12.5%. I doubt any current PC3200 can be overclocked even a few percent.

The math works like this: RDRAM on the i850E chipset is dual channel. Each module is 16-bits, but making the two channels parallel gives you 32-bits. PC1066 uses DDR technology similar to DDR SDRAM, so even though it operates at 533MHz, it's DDR1066 rate. But only 32-bits.

So you mulitply 1066x32, then divide by 8 to go from megabits to megabytes, then by 1024 to go from MB/s to GB/s, and you get 4.2GB/s

PC3200 needs no math, just divide by 1024 to get GB and you have 3.1GB/s. But if you want to do the math, PC3200 is DDR400, which means it's 200MHz with DDR. But it's also 63 bits wide. So if you do similar math, 400x64/8/1024, you get 3.125GB/s.

<font color=blue>By now you're probably wishing you had ask more questions first!</font color=blue>

 

[bum_jcrules]

Skater,

Correct... My bad to cross the two. I hate it when I have senior moments. My birthday is Wednesday, I wonder if it has anything to do with it. I have been doing that too much lately. (Just call me nuts...)

The DDR standard was originally written up to DDR333. However they left a caveat in the original document that states thus on Page 15.

<A HREF="http://www.jedec.org/download/search/JESD79R2.pdf" target="_new">"In addition to the above DDRxxx specification, a letter modifier may be applied to indicate special timing characteristics for these devices in various market applications."</A> - - <i>JEDEC STANDARD - Double Data Rate (DDR)SDRAM Specification - JESD79 (Release 2)- MAY 2002</i>. Again this is from the second version of the original.

Just for the others that might be wondering what DDRII is.

DDRII will be using SRAM registers at the end of the rows.

Here is what <A HREF="http://www.lostcircuits.com/memory/eddr/8.shtml" target="_new">Lost Circuits</A> had posted 2 years ago.

Here is what JEDEC has posted regarding <A HREF="http://www.jedec.org/DOWNLOAD/pub21/HotDDR/DDR_II_evolution.pdf" target="_new">the DDRII standard</A>.

It goes all the way up to DDR667 with the ~333MHz signal. I am sure that will have a caveat too. It isn't written in stone yet.



pball68,

Sorry to get off topic. Crash is correct for bandwidth at this stage of the game. Until there is "Real" DDR400 or PC3200 out on the market that is not just overclocked PC2700, RDRAM is still king. The future peak memory bandwidth is on the side of DDR SDRAM but RDRAM is king right now. So it has the "speed" (Frequency) and the peak bandwidth advantage. And when dual channel is available for DDR at the DDR400 and a FSB to equal the memory bandwidth, DDR will be king for sure. Even if RDRAM reaches 600MHz aka PC1200.


<b>"If I melt dry ice in a bathtub, can I take a bath without getting wet?" - Steven Wright</b>

 

[pball68]

So if I buy one, which should I buy now for speed (possibly taking the future tech advances into consideration)? DDR PC3500 256K or RDRAM 1066MHz 256K?? Thanks

 

[Sunny129]

not that this has much to do with the actual inquiry about the difference in RDRAM abd DDR SDRAM, but there does exist "real" PC3500 memory. it is being sold by a company by the name of GEIL. this PC3500, or DDR433, runs at 433MHz and moves roughly 3.5GB of data per second, or more accurately 3500/1024 = 3.4GB/s. it may be OCed, but its been tested successfully at 433MHz, or else this company would not be able to sell a product labelled PC3500. anyways, since nothing higher than PC2700 is an industry standard yet, you could say this PC3500 is as "real" as PC3000 and PC3200. now i've heard that this company might just be OCZ reincarnated under a new name so as to avoid being identified as OCZ. this is enough reason for me not to take a chance with this PC3500 stuff...especially when you can get PC3200 from reputable memory and chip makers such as Samsung and Corsair. maybe i'll start looking into it when PC3200 becomes an industry standard and more big names in the memory market start making unofficial PC3500 successfully. but until then, i'd wait to see some PC3500 from Samsung, Corsair, Mushkin, or Crucial, even if its unofficial b/c JEDEC hasn't standardized DDR433 yet...but thats just my opinion...

 

[Dinski]

Grab the RDRAM PC1066 , fellow! It's not only faster, but also overclockable.


<font color=orange>ÃÎËßÌ ÇÀËÚÊ ËÀÏÍÈ, ÃÎËßÌÀ ÙÀÍÃÀ ÂÄÈÃÍÈ!</font color=orange>

 

[bum_jcrules]

This is the big question...

What platform will this be for? Intel or AMD?

That will say a lot...

<b>"If I melt dry ice in a bathtub, can I take a bath without getting wet?" - Steven Wright</b>

 

[Crashman]

If it can't be powered by most boards at the claimed speed because it uses nonstandard voltage, it's simply a lower speed memory that's been overclocked.

<font color=blue>By now you're probably wishing you had ask more questions first!</font color=blue>

 

[pball68]

I will use intel. Not into overclocking either. Just normal gameplay.