What's the difference between Unbuffered and Registered Ram?

[jagr10]

I'm looking at ram and there are so many different types of DDR so i noticed some said unbuffered, and others say registered. What is the difference? which is better?

Also, what does CAS2 or CAS 2.5 mean?

 

[acronym]

Registered memory, sometimes referred to as buffered memory, is generally used in situations when adding 512Mb or more of RAM on the motherboard. Also, the more chips on the memory modules, the more important it is to use registered memory. This is because the high-profile modules use 32-36 chips each. Adding the 'registered' feature gives these high profile modules added stability in your computer system by placing registers between the module's interface and the actual SDRAM chips on the PCB. This helps to decrease the 'loading' and allows for more physical SDRAM devices to be placed on a single module.

CAS Latency (Column Access Strobe latency) is defined as the speed at which you access a single column of RAM.

 

[LintMan]

Just to add a few things... I don't think either form is necessarily "better", although unregistered RAM is cheaper and so probably preferable if you don't need the registered stuff.

How do you know which you need? It depends a lot on your motherboard. Memory maker Crucial (http://www.crucial.com) has a great site where you can pick your motherboard from a big list, and it will show you all the memory types that support it (at least from those they make), and if you click on the motherboard spec link from that page, it gives details on all the memory types the board supports. Very nice.

 

[jagr10]

I looked at crucial's site and all of their DDR ram for the Epox board is unbuffered. So if i were to get 2 sticks of 256MB unbuffered, would that be ok or should i look elsewhere for registered?

 

[acronym]

Crucials 256meg modules have only 16 chips. There is no reason to pay the extra $ for registered memory unless your motherboard requires it (which it doesn't)