Is DDR2 Compatible with RDRAM? Help Me Upgrade My System!

[Argentum Vulpes]

I'm in the process of updating my four year old system. This will include a new Motherboard, CPU, Memory, Video, and HD (if I need to a new power supply). Here is a list of what I'm planning on running

CPU:
P4, 3.0Ghz, 800Mhz FSB, 1MB L2 cache, HT tec.

Memory:
184 pin, 512k, Non-ECC, RDRAM PC-800

Video:
nVIDIA GeForce 6600/300MHz, 128MB, PCI-Express x16

HD:
80GB, IDE ULTRA ATA133

The problem I run into is trying to find a motherborad that will run this all. I can find plenty of DDR2 boards, however they have the problem of only running the memory at 400Mhz clock speed. This is unacceptable for me as I want to get the entire system to run at the best clock speed, and I see this as 800Mhz with RDRAM. As a side note overclocking is not an option for me because I don't have enough time or motivation to learn it and do it right. So if anyone can point me in the direction of the motherboard I need or clear up any misconceptions I have about DDR2 please help me.

 

[russ_watters]

There are several issues with RDRAM:

-High latency: ~30ns vs ~5ns for DDR SDRAM.
-16 or 32 bit vs 32 or 64 bit for DDR SDRAM (double the memory bandwidth).
-DDR2, IIRC transfers data 4x per clock tick just like RDRAM
-That 800mhz is actually 200mhz quad-pumped (ddr 400 is 200x2).

Add all that together, and DDR SDRAM is faster, which is why RDRAM is pretty much dead. According to my Sisoft Sandra benchmark software, PC800 in dual channel will give you about 1400MB/s while PC3200 DDR Sdram (not ddr2) will give you 1700.

 

[anti_crank]

The newer DDR2 motherboards have speeds now greater than 400mhz, so the numbers are getting better. RDRAM was prohibitively expensive, and also the fact that you had to run them in pairs was bad.

If you want to run DDR2, you'll need the new motherboards based off the 915 or 925 chipsets. Intel makes a good board, and so does Asus. Note two things - one, for these boards, you need the new LGA775 processor, not the S478 ones. (So you'd be looking for the Intel 530 or so processor.) Two, if you get a motherboard with the 925 chipset, then you need a 24-pin power supply, which is not the normal kind. They aren't much more expensive, but different.

 

[walias15]

There are several issues with RDRAM:

-High latency: ~30ns vs ~5ns for DDR SDRAM.
-16 or 32 bit vs 32 or 64 bit for DDR SDRAM (double the memory bandwidth).
-DDR2, IIRC transfers data 4x per clock tick just like RDRAM
-That 800mhz is actually 200mhz quad-pumped (ddr 400 is 200x2).

Add all that together, and DDR SDRAM is faster, which is why RDRAM is pretty much dead. According to my Sisoft Sandra benchmark software, PC800 in dual channel will give you about 1400MB/s while PC3200 DDR Sdram (not ddr2) will give you 1700.

although you are correct with your above conversion remember DDR ram is actually less efficient in the utilization of its bandwidth only able to utilize about 65% of its bandwidth to where Rambus is able to utilize about 85% of bandwidth so the performance is actually about the same of the 2 in real life situations the rambus actually is slightly faster then the ddr keep in mind that rambus is also offered at a higher clock speed with the 1066 rambus but the slight performance margin is way less then the margin of cost so take that into consideration when upgrading

 

[Pengwuino]

RDRAM is slower in real life tests so that should about sum it up for you :P