DDR double vs. single sided, banks and more!

kwo

Golden Member
Mar 18, 2002
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Hi everyone!

I have a technical question relating to DDR memory.

Is it true that most DDR compatible motherboard can only function with *6* banks of DDR memory?

And is it also true that, in general, a single sided DDR module (memory chips on one side only) has one "bank" of memory whereas a double-sided module has two "banks".

Hence, by extension, you can only have a maximum of 3 double-sided or 2 double-sided + 2 single-sided DDR memory modules?

Case in point: I have a Gigabyte 7N400Pro motherboard currently with 2x512mb Kingston HyperX PC3200 (KHX3200AK2/1G) double sided DDR modules for a total of 1GB of system memory.

I wanted to double my memory by buying another 1GB of memory.

I bought the exact same set (2x512mb KHX3200AK/1G) to fill the remaining DIMM slots (four DIMM slots total).

However, that would give me four double-sided DDR modules for a total of.... 8 banks?
So, would that therefore not work in this computer???

 
 

Heidfirst

Platinum Member
May 18, 2005
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You would need to check the manual for that mobo.
The Gigabyte was unusual for an nF2 mobo in having 4 slots - most only had 3.

Certainly 939 boards will run 4 slots (8 ranks) albeit at reduced speeds or command rate.
 

kwo

Golden Member
Mar 18, 2002
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thanks for the response - I gave myself a crash course on memory, banks, and the nForce2.

Turns out I was right - it won't work. So, am sending it back! Glad I didn't open it!

Ran
 

aka1nas

Diamond Member
Aug 30, 2001
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It depends completely on the chipset/memory controller as to how many banks it can handle. Double-sided DRAM is always 2 banks AFAIK. I don't recommend using cheap RAM that has weird memory chip configurations. I once saw a DIMM that only had 4 chips and was single-sided. I had no idea how it managed to function.
 

Peter

Elite Member
Oct 15, 1999
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It's "ranks" not "banks" please. (This is because DRAM chips have banks internally, 4 or 8 these days.)

Now, double-sided DIMMs. These may very well have just one rank. This happens when the DIMM is made from 4-bit-wide DRAM chips. You'll need sixteen of those to make a 64-bit-wide DIMM, 18 for an ECC-enabling 72-bit-wide one. Using x4 DRAM is popular with ECC DIMMs, because the advanced ECC engines of today then can compensate the loss of an entire DRAM chip without crashing the machine.

Standard PC DIMMs made from x4 DRAM aren't too common an occurance, simply because not all chipsets can run them.

Similarly, and solving aka1nas's mystery, one can just as well use 16-bit-wide DRAM chips to form a single 64-bit-wide rank from just four chips. No miracle, nothing weird about it.