whats the Diff between RAM speeds

[pctechnician]

I see RAM speeds all the time: PC 2100, PC 2700 etc. what exactly does that mean? how does that work according to the motherboard speed?

Also i thought that motherboard speeds only ran at 100 MHZ, 133 MHZ. How are some speeds like 266 MHZ or 333 MHZ or even 500 MHZ?

 

[cdogg]

PC2100 == DDR 266
PC2700 == DDR 333

Take DDR 266, for example. It runs at 133MHz, but is able to send twice as much data per clock cycle as regular PC133. Thus, they often say it's running "effectively" at 266MHz, although it's really on a basis of 133MHz.

Plus, DDR's cas latency is much more advanced than PC133.

Motherboard buses work the same way. Intel's current top-end models run on 533MHz (133x4). They've simply found a way to widen the bus so that 4 times the amount of data can be transferred.


~cdogg

"The secret to creativity is knowing how to hide your sources."
- A. Einstein

 

[pctechnician]

So why do they call it PC 2600 for example? What does 2600 have to do with anything?

 

[cdogg]

No significance as far as I know. RDRAM uses names like PC800 (400MHz) and PC1066 (533MHz), but these names are in no relation to PC2100 and PC2700 for DDR.

Look at it like a version number. The higher the version number, the newer and faster it is.


~cdogg

"The secret to creativity is knowing how to hide your sources."
- A. Einstein

 

[dgrandy]

The 2600, or 2700 signify the bandwidth of the memory, 2700 RAM can theoretically transmit 2.7 GB of data per second, its usually a little lower than this though. RDRAM doesn't give the bandwidth like DDR RAM, they just show the speed.

 

[cdogg]

dgrandy is absolutely right.

Here's a nice little summary for DDR:

http://www.kingston.com/newtech/ddrbandwidth.asp

Also, just wanted to add that the '800' and '1066' in PC800 and PC1066 stands for the memory clock in RDRAM, which is double the speed of the bus. Sometimes you'll see PC800 stated as RIMM3200 (3200 == 3.2GB/s), and PC1066 as RIMM4200 (4200 == 4.2GB/s).

more on RDRAM:

http://www.kingston.com/newtech/rambusbw.asp

~cdogg

"The secret to creativity is knowing how to hide your sources."
- A. Einstein