Registered RAM is defined by Crucial, in their glossary, as
-----------------------
Registered Memory
Registers delay memory information for one clock cycle to ensure all
communication from the chipset is collected by the clock edge, providing a
controlled delay on heavily loaded memories.
-----------------------
Registered is the highest level of memory error correction = ECC RAM
available. ECC memory, tests for, and corrects errors automatically, very
often without the operating system being aware of it, When writing the data
into memory, ECC circuitry generates checksums from the binary sequences in
the bytes and stores them in an additional seven bits of memory for 32-bit
data paths or eight bits for 64-bit paths.  When data are retrieved from
memory, the checksum is recomputed to determine if any of the data bits
have been corrupted.  Such systems can typically detect and automatically
correct errors of one bit per word, and can detect, but not correct, errors
greater than one bit.

Both Registered RAM, and ECC RAM is designed for Servers, or mission
critical workstations, where any error can be problematic. The user penalty
for using such RAM is performance. Obviously, if every bit has to be
checked, then performance will suffer.

You will have to check your manual to see if your motherboard supports
Registered RAM. Registered and ECC MUST be supported by your motherboard.
This will be clearly stated in the motherboard manual. New Registered and
ECC are expensive, and you rarely find Registered RAM on anything but a server.

Unlike ECC RAM, Registered RAM will NOT mix with other types of RAM. You
can put ECC RAM with normal unbuffered RAM and it will default to the lower
specifications of the unbuffered RAM. But in order to use the ECC, all
DIMMS or SIMMS must be ECC.

I recently bought some Crucial P133 ECC Ram on Ebay. I discovered that many
sellers were selling Registered RAM as ECC RAM, without pointing out that
the DIMMS were, in fact, Registered RAM. This was probably because the
sellers were not aware of the difference, and the RAM probably was pulled
out of old servers. Registered will not run on a normal desktop setup,
certainly not if mixed with unbuffered RAM. So if you buy ECC ram from Ebay
make sure you stick with a brand name and get a model number, so you can
check with the manufacturer.

Rode
The NOSPIN Group
http://www.freepctech.com/rode/



At 11:39 AM 10/12/2005, you wrote:
>This is for the memory experts. What exactly is "registered memory" in
>SDRAM, and can such memory be used with chipsets such as the Intel 845?
>Thank you.
>Peter
>[log in to unmask]

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