Memory questions (double sided, double ranksed, dual channel)

[AndiC]

I have read several books on memory and have become a little confused wiki has'nt really helped.
I don't seem to be able to find enough information on workings at the level i am looking for.

In the Meyers book he states that double sided memory has DRAM's both sides of the DIMM.
Whilst this is true for "physically" double sided DIMM's, in fact the term "double sided" means how the
DRAMS are logically stacked together and can be indeed on both sides of the DIMM, however, also can still be on a single side... i'll come back to this later.

Double ranked is when to DIMM's are paired (slots paired) together ie 2 x 64 bit means that a 128bit memory bus is available. MMC's can have a 128bit memory bus right?

Dual channel i am not so sure about this, i believe the memory controller has 2 pipes so it can do two different task at same time. (2 different banks, not the same of course).

my questions are

Double rank have i got this correct?

what are differences between Double rank and Dual channel? is Double rank just a larger bus one operation a time,when Dual channel can do more that one operation on two different banks.

what is the difference between double sided and Double ranked, is double sided same as having 2 dimms in a single slot acting same as Double ranked ?

I hope you can help?

Andi

[AndiC]

I thought i would update as i find stuff out

Memory seems to be made up in blocks called "Ranks", each rank is 64bits wide.

DIMMS can be single, dual or quad rank.... single side - single rank, double sided = dual rank ????

(should be really called double banked etc)

Double Ranked DDR means that two slots are ranked together making 128 bit memory bus.

(paired banks)

AC

[kevicho]

Originally Posted by AndiC

I thought i would update as i find stuff out

Memory seems to be made up in blocks called "Ranks", each rank is 64bits wide.

DIMMS can be single, dual or quad rank.... single side - single rank, double sided = dual rank ????

(should be really called double banked etc)

Double Ranked DDR means that two slots are ranked together making 128 bit memory bus.

(paired banks)

AC

I always thought Dual channel was more to do with the sending of information in memory to the CPU via a bus using matched pairs (2 identical mem sticks) on a compatible pair of memory slots.

This looks like a good place to start (altho wiki shouldnt be taken as gospel ever)

http://en.wikipedia.org/wiki/Dual-channel_architecture

[greenbrucelee]

A DDR DIMM can run by itself but not in dual channel mode, to acheive dual channel two matching pairs must be installed, they must be identical in latency etc.