PCA Forums

well, i just got turned on to the ddr memory and i ordered a system that has ddr memory. but i have been noticing some chips that are rambus.

for the sake of saving me a couple hours reading, what exactly is rambus? is that what they are calling RDRAM? how does it compare to ddr?

also, if i had a motherboard, say a gigabyte ga-7dxr+, which can support either ddr memory or sdram, could i put a 256 mb ddr stick in and also put a 256 sdram stick in one of the other slots? i would normally do some trial and error, but my parts have not arrived yet, and i figured someone out there probably already knows.

- Rambus = RDRAM

- Rambus memory uses a higher clockspeed but a narrower datapath compared to DDR/SDRAM memory.

- All mobos I know with mixed memory slots allow only one sort to be used, no mixing of different memory technologies allowed.

http://www.crucial.com/library/ddr_vs_rdram.asp got more details on DDR vs Rambus.

thanks for the info. the only reason i was wondering about rdram is because i noticed some of the dell dimension PCs were using rdram now.

from what i have read now, it does not look like rdram would do anything extra special for me at this time. i think i will be just fine for now with a crucial 256 mb ddr pc2100. and the way memory prices are now, i could always get another if i need to.

RDRAM is what Intel came out with 2-3 years ago. It is often clocked at .... 800mhz? That's the name they gave it in the couple of Dells we got with it.
It was VERY expensive, more so than ECC SDRAM used in many servers, and did not deliver the system speed increase it alleged to ( tho it helped ) so most manufacturer's moved away from it. Then DDR SDRAM came along. It is as fast or faster, at least for the end user, and MUCH less expensive. So even mighty Intel has come out with a chipset supporting DDR now

BTW, the GA-7DXR+ does NOT support both DDR and SDRAM. It has the AMD 761 chipset which is DDR only.

RDRAM is what Intel came out with 2-3 years ago. It is often clocked at .... 800mhz? That's the name they gave it in the couple of Dells we got with it.

Actually, PC800 RDRAM is clocked at 400 MHz, it's double-pumped (DDR) for an effective 800 MHz.

It was VERY expensive, more so than ECC SDRAM used in many servers, and did not deliver the system speed increase it alleged to ( tho it helped ) so most manufacturer's moved away from it.

Though the prices now are about equal.

thanks for the info. the only reason i was wondering about rdram is because i noticed some of the dell dimension PCs were using rdram now.

Actually, Dell's used it for a couple of years. They first started with the PIII on i820 chipset, which was a single-channel solution. Meaning, you did NOT have to install memory in pairs. i820 died pretty quickly due to:

- cost. at the time, RDRAM was really expensive, around $800 for a 128 MB stick.
- Performance. Though it wasn't bad by any means, it wasn't worth the hype and the cost. PC800 gives a theoretical bandwidth of 1.6 GB/s, but the front-side bus was still limited to 133 MHz (1.06 GB/s). Add to that the higher latency of RDRAM and even more latency due to the FSB and memory running asynchronously.
- Bugs. The 11th-hour delay of the VC820 boards (unstable with more than 2 RIMMs), and the MTH bug that killed the SDRAM version basically turned people away from i820 in droves.

i840 was pretty solid, it was a PIII chipset with a dual-channel memory system which performed pretty well. The dual channels combined with the i840's prefetch cache hid much of the latency, but you still had the 133 MHz FSB as a bottleneck.