Did I understand DDR spec correctly?

[egravel]

Hi,

I'm trying to build a new computer system and I pretty much figured out what I want and
understand for the most part all the new mainstream technology. There's just one that's
bugging me: DDR.

Questions:

1. is PC2100 266MHz a pure 266 clock speed or is it 133 double because of the operation
that can take place on rise and falls of click ticks?

2. when they say rated 2.5-3-3 @ 133 MHZ what does this mean? Is this the latency?

3. Is 128-Megabit chips a good thing?

4. What is a 16Mx64 Module? Is there other types? Which is best?

5. Again what is 16Mx8 Chip Density? ...?

6. What is 6-Layer PC?

7. When would I choose to go with unbuffered over registered?

8. Looking at Corsair's DDR technical sheet, they talk of organization (16Mx72) and
RAM type (16Mx8), what is this?


Most of the above question came from reading:

http://www.mushkin.com/cgi-bin/Mush...22114d080c27400a0001020539+EN/products/990708


Thanks,

Eric

 

[w74656]

1. It's 133MHZ doubled to 266
2. this is the latency
3. It's the density, how much each chip can hold
4&5&8. Someone else can explain that
6. You mean a 6-layered PCB, the PCB that they mound the chips on has six layers, usually it iproves signal clearity
7. Unbuffered, unregistered for cheapest price and speed

 

[Shagga]

A good place for all the gen on RAM and terminology is here at Crucial

 

[Erasmus-X]

1. No, the true clock speed would be 133MHz (derived from the external bus clock). It runs effectively at 266MHz because the memory can complete a cycle off the falling and rising edges of the clock.

2. CL 2.5 is the latency of that particular module, running at 133MHz FSB.

3. 128Mb (megabits) is a different way of saying that there is 16MB of density per chip (there are 8 bits in a byte, thus 128Mb = 16MB). It can be either a good thing or a bad thing, depending on how much total memory capacity that stick of RAM has.

4. A 16Mx64 module is again a megabit measurement, totalling 1024Mb. This particular stick of RAM is a 128MB stick, because it has 1024 total megabits made up of 64 different 16Mb cells.

5. This means that there are 128Mb total per memory chip on the PCB, and that there are 8 of these chips total. This means that this particular stick of memory is again, a 128MB in capacity.

6. A 6-layer PCB basically tells you that it's most likely a quality PCB. The more layers the PCB has, the more space there are between the traces, thus eliminating problems with noise interference. Cheaper memory PCBs (commonly found on generic memory) use 4-layer processes, making them more unstable for high-performance use (like overclocking). It always pays off to buy memory sticks from a reputable vendor. With memory prices this low, it's pretty stupid not to. For example, ordering quality memory from Crucial's website gives you free shipping, which pretty much makes up for the extra $10 you spent on their memory. It's pretty much a no-brainer.

7. Registering is a method used commonly on server memory that allows the memory PCB to support a greater number of modules. A register (or buffer) is placed on the memory to redrive control signals on the memory chip. Because of this, registered memory is noticeably slower than unbuffered memory. For your uses, unbuffered memory is sufficient. You cannot mix unbuffered a registered memory together.

8. Hmmm....can't answer that one.

If you have more questions, Kingston's Ultimate Memory Guide is an excellent resource.