Different types of DDR?

[Webhead211]

hey all, i'm intersted in buying some PC2100 DDR ram, and i went to crucial's website, where they're having this pretty good sale, but they have three different prices for 256mb DDR. Can anyone tell me exactly what the difference is between (DDR PC2100 • CL=2.5 • Unbuffered • Non-parity • 2.5V • 32Meg x 64) and (DDR PC2100 • CL=2.5 • Unbuffered • ECC • 2.5V • 32Meg x 72 ) and (DDR PC2100 • CL=2.5 • Registered • ECC • 2.5V • 32Meg x 72)? from left to right they are cheapest to most expenseive. i'm just wonderign if there is a huge performance difference or anything. and whats's unbuffered?

thanks,

webhead211: Quality at it's Finest

[Edited by webhead211 on 04-05-2001 at 12:55 PM]

[paulc]

All 3 types are JEDEC standards. From the Intel and IBM JEDEC documents I've read, there are different timing structures for the 3 different standards. http://www.chips.ibm.com/products/memory/ddr_memory_enablement/ddrregdesign/ddrregrev1.0.pdf

I bought the cheapest 256MB DDR DIMM (unbuffered, non-parity) from Crucial this week and others have it working fine on AMD761, ALi Magik and KT266 boards. ECC DIMMs have error correction. I don't know if all the above chipsets support it or not. All the performance from the 3 types will be the same... CAS latencies of 2.5:3:3 and 133MHz DDR memory bus speed. The differences weren't important to me, so I just went for the cheapest one.

[OvrrDrive]

My manual on my a7m266 states that it does support ecc ram; however, when I enabled it in the bios I couldn't even get a post. It went completely dead until I reset the cmos.

Buy the cheap stuff!

[The Navigator]

If you already have a PC and are unsure which type you have, count the number of small, black, IC chips mounted on one of your existing DIMMs. If the number of chips is evenly divisible by three, then you need ECC. If the number of chips is NOT evenly divisible by three, you have non-parity memory.

If you are building a PC and deciding which type to use, the following guidelines should help. If you plan to use your system as a server or a similar mission critical type machine, it is to your advantage to use ECC. If you plan to use your PC for regular home, office, or gaming applications, you are better off with non-parity.

ECC (Error Checking and Correcting) performs "double bit detection and single bit correction." This means that if you have a single bit memory error, the chipset and memory will find and repair the error on the fly without you knowing that it happened. If you have a double bit memory error, it will detect and report it. Using ECC decreases your PC's performance by about 2%. Current technology DRAM is very stable and memory errors are rare, so unless you have a need for ECC, you are better served with non-parity SDRAM. Do not mix the two.
CL2 parts process data a little quicker than CL3 parts in that you have to wait one less clock cycle for the initial data. However, after the first piece of data is processed, the rest of the data is processed at equal speeds. Latency only affects the initial burst of data. Once data starts flowing, there is no effect. Bear in mind, a clock cycle for a PC100 module is 10 nanoseconds so you probably won't notice a significant performance difference. Most systems will accept either latency part. However, there are some systems that require either CL2 or CL3 parts.