On Fri, 02 Apr 2004 03:16:37 +0100, Paul Bassman wrote:

Hi Folks,

Have been playing about with PC's for 25 years just as a hobby, and am
completely addicted. I want to buy the Athlon 64 FX53, am ready to order.
One thing is stopping me and I hope you can help. I haven't a clue what
registered ram is? It say's in most reviews of the Evesham PC the firm of
choice, that the registered ram is slow, so, please can you tell me, does
this defeat the object of playing games for example. I would have my Choice
of a very fast CPU fast hard drive etc, but the ram would bring speed down
to say a XP 2000, do you think Rambus ram could be used with this
motherboard, just what the eck is registered ram and why is it slow?
Thanks!!
Paul.

Registered RAM has a set of registers on the address and control lines.
The registers reduce the load on the lines and they also reduce the length
of the lines. If you have an unregistered DIMM with 8 RAMs then the
address and control lines from the processor must drive the 8 RAMs
directly, i.e. there are 8 loads on the each line. Also the lines must
travel from the processor, up onto the DIMM and then fanout to the RAMs on
the DIMM. On a registered DIMM the lines from the processor drive the
input of the register, 1 load instead of 8. In addition the lines
terminate at the register which is placed near the connector so the length
of the lines are much shorter. Registered DIMMs significantly improve the
signal quality of the address and control lines. Systems that use
registered DIMMs can support more memory then those that use unbuffered
DIMMs. The downside is that there is a small increase in the access time
(bandwidth is uneffected). As a practical matter the performance loss from
the increased latency is very small, completely unnoticeable in fact. On
the otherhand the performance gain from having more RAM is huge. The
improved signal quality also improves the reliability of the system. On
top of that registered RAMs always include ECC (error correcting codes)
which will correct single bit errors and detect double bit errors.
Unbuffered DIMMs are available with ECC but they usually don't include it.
So an unbuffered system is less reliable for two reasons, the signal
quality is worse so there is increased probablility of an error, and if
there is an error there is no way to detect it let alone fix it.
Registered systems have better signal quality so there is less likelyhood
of a bit error and they have ECC so even if you have a bit error the
processor can correct it.