diffferences in ram

[benchristian]

What is the difference between SDRAM, the new ram that comes with the P4 (Rombus?) and...there's another type of newer ram, but i forgot what it's called (i'm talking about system memory, not the DDR ram in new video cards).

Thanks

[daveleau]

There is Rambus, DDR, PC133 and PC100 RAM on the market right now. The PC150 is not really what it is marked as. For more info go here: http://peripherals.about.com/compute/peripherals/gi/dynamic/offsite.htm?site=http%3A%2F%2Fwww.crucial.com%2Fli brary%2Fddr_vs_rdram.asp

Dave

[Dputiger]

In a nutshell, here's how it breaks down.

SDRAM is a slower technology that transfers data in 64 bit (8 byte) bursts. The memory bus can transfer 64 bits in a single cycle at 133, 100, or 66 Mhz, depending on your memory clock speed. This leads to a total bandwidth of 1060, 800, or 528 Megabytes a second. SDRAM can have a relatively low latency time (2 or 3) and adding additional pieces of RAM into your RAM slots does NOT reduce access time.

RDRAM aka Rambus Memory, uses a different approach. Rather than moving data at slow speeds but moving lots of it (SDRAM), RDRAM moves a very small amount of data at very high speed. The memory bus on RDRAM is only 2 bytes wide, compared with SDRAM's 8-bytes. RDRAM, however, can run at speeds of 800 Mhz or even faster.

PC800 RDRAM has a theoretical maximum bandwidth of 1.6 gigabytes a second.

RDRAM, however, has some serious drawbacks:

1) Cost: Until very recently, RDRAM costs were 4-5 times what SDRAM was.

2) Performance: Intel over-hyped RDRAM for the PEntium III, but, unfortunately, RDRAM doesn't perform well at all with the P3's 133 Mhz bus. SDRAM solutions beat out RDRAM ones consistently, as even Intel's benchmarks showed. Only now with the P4 has a performance benefit become aparent from RDRAM

3) Lies and stupidity: Rambus flat-out lied about RDRAM performance to the user market, as did Intel. Plus, Rambus is now suing everyone in site and attempting to claim ownership of the entire DRAM market. This, probably more than anything else, has led to a tremendous backlash against RDRAM.

4) Data Transfer: RDRAM only has a single-channel for data to pass out of memory. As additional RIMM modules are added to a system, the latency on the total memory bus increases, slowing performance.

A simple way to understand the difference between RDRAM and SDRAM's method of transferring data is this:

SDRAM can 'array' data out of itself--in RDRAM, data passes out in a queue, through a single channel. Hopefully that makes sense.

[rock8785]

I havent heard of RIMM before, what is that?

[socalgal]

RIMM is the trademarked name for a Direct Rambus memory module (http://www.kingston.com/tools/umg/newumg05a.asp)