RDRAM=Cheap mainboards! I think not!!

[FastD]

I read the Intel Developer Forum Conference - Spring 2001: Part 1 .. It is stated there, and has been before by RAMBUS that RDRAM will let mainboard manufacturers use cheaper 4 layer pcb designs as opposed to 6 layer pcb.

But why are all current P4 maiboards 6 layer then?? (I am aware that was in the article as well).. Furthermore.. here in Sweden a p4 mainboard is about $300, an Asus 760 DDR board is about $220! And that is supposed to be a more expensive design wasn't it?!? Furthermore the P4 boards have been available slighty longer here than the DDR boards.. So the DDR boards will most likely drop a little as soon as there is a sufficient supply.

So.. my question is.. why isn't RDRAM making the p4 boards cheap?


OK. nuff about that.. I was thinking.. What is stopping AMD.. Or anyone else from making a dual channel sdram chipset?? I think it's pretty safe to say that DDR is a disappointment performance wise so far. Only yielding performance improvements of about 0-10% in real world applications. And maybe 20% in theoretical memory bandwidth benchmarks. A dual sdram sollution would easily outperform both DDR ram and RDRAM and memory would be CHEAP!

Or is it just too complicated to make such a chipset? As stated in the Intel Developer Forum Conference - Spring 2001: Part 1, most KT133 mainboards are 4 layer designs. Would it be so hard making a dual channel memory controller and fit that in there somewhere?

PC166 sdram is just around the corner (some memory chips are already working at that speed, and even higher) A dual pc166 sollution would offer a theoretical bandwidth of about 2,6gb/sec. Not quite as much as dual RDRAM. However I believe that it would deliver a higher real world performance and certainly lower latencies. Not to mention MUCH lower prices.

Take the sisoft sandra memory benchmark.

DUAL channel RDRAM achieves around 1400mb/sec which is about 43% efficiency.
DDR ram achieves around 750 mb/sec (MAX) which is about 35% efficiency.
Pc133 SDRAM Achieves around 600mb/sec which is about 55% efficiency!


This means that a dual channel pc133 or pc166 would perform almost as good , or on par with a dual channel rdram solution in theoretical mem benchmarks such as the sandra and it would almost certainly seriously outperform the RDRAM solution in every other benchmark due to higher overall throughput and lower latencies! Maybe intel's Brookdale sdram chipset will be dual channel sdram??

That would explain why intel is toning it down so much.. They know it will outperform the RDRAM solution they have now AND be much cheaper!

Pure speculation all this ofcourse

 

[lifeguard1999]

As I have read elsewhere, dual DDR is difficult due to the number of pins involved. I would suspect that dual PC166 would not be much easier.

We already have:

PC1600 = 100 MHz * 2 DDR * 8 bits/byte
PC2100 = 133 MHz * 2 DDR * 8 bits/byte

So I can see where a :

PC2667 = 166 MHz * 2 DDR * 8 bits/byte
PC3200 = 200 MHz * 2 DDR * 8 bits/byte

are possible since they are used on graphics cards already. However, it appears that quad data rate (QDR) will be used instead. The problem now is the limited supply of this faster memory.

 

[FastD]

But then why are most kt133 boards 4 layer and all 760 boards 6 layer designs??

 

[Demon-Xanth]

6 layer designs are less noisy by the fact that the power planes are further apart. In my experience a 6 layer board should not make much more than $20 if not $10 difference (incl. development) on the end board price. A major factor in the P4 board price is the $75 i850 chipset vs. most chipsets in the $30-40 range. Also the high frequency RDRAM requires tighter tolerences in the trace shapes, widths, and spacing.

A 4 layer vs. a 6 layer can be seen when looking at a $125 board vs. a $145 board (although often there is much more differences). Anyone saying "My board is $150 more expensive because of the 6 layer PCB" is just trying to pull a snow job. And for the curious, yes, there is 8 layer PCBs.

 

[FastD]

OK.. then why won't anyone make a dual... or even quad channel sdram chipset??

 

[fitzhue]

Thats a very good question FastD
Anand reviewed a chipset by Serverworks that can be found here
They have a pc133 interleaved chipset.
I would think if they could do it, then AMD or intel could implement this very easily.
Anybody have any incite?

 

[Demon-Xanth]

The Ali-7 chipset interleaves two SDRAM banks, but it sucks so bad at everything else (including just accessing ram) that I don't know of anyone that used it. And I believe some macs also interleaved banks. nVidia's Mamba is rumored to be interleaving banks, but that's vaporware.

 

[NOS440]

The simple Answer to this question is "Supply and Demand" the demand isn't high enough yet for the P4. Look at the cost difference between the Intel 850 board and Asus and others. Intel Motherboard are usually the most expensive. Intel is keeping the pricing as competitive as they can and still regain there development money. They have dropped there prices quite nicely so far and as demand goes up prices will drop further.

Also I would really rather have a 6 layer PCB motherboard they are known to have better signaling.