128X4 v.s. 64X8 DRAM? I'm Confused.

[dissembled]

I am working up my shopping list and while looking at what RAM to buy, I ran across some RAM that said it uses 128X4 DRAM chips. It goes on to warn that some motherboards require 64X8 DRAM chips and may not be comaptible.

This is new to me and I'm confused. I am planning on the ASRock 939Dual mobo and looked through all the documentation I could find on ASRock's website but there is no of this discrepancy, just 184pin DIMM.

Anyone have any insight into this?


This is what I am planning on:

ASRock 939Dual mobo
AMD 3X00+ RevE
2x1GB 3200 Ram

 

[FlyGuy]

While I can't be certain with DDR, some newer PC133 RAM didn't work in the older mobos because it was high density and half the memory would be recognized. 128x4 is high density if I recall but I haven't seen anything recently about compatibility problems so maybe it's just an old, left-over message.

I bet that Ape guy can give you the in-depth info though!

 

[fainis]

be very carefully if you consider dual channel...amd64 has an internal mem controler..
in other words the modules must be identical (for amd)
128x4 or 64x8 is called the memory structure and the 512 is their capacity
it is also important whether the modules are single side or double side..read also the mainboard info
i hope this helps

p.s. excuse my bloody english

 

[dissembled]

I read through everything I could find on ASRock's website regarding the memory compatibility. All I can find is 184pin DIMM.

Perhaps I should simply sidestep this problem by buying from someone else who claims "Compatibility Guaranteed".

 

[fainis]

184 pins is ddr 1 standard...
just make sure the modules are buying are identical .....it don`t matter whether they are 128x4 or 64x8....

 

[nobly]

This is an indepth explanation from:
http://hardware.mcse.ms/message153112.html

You need to be careful. Typically what I suggest is that you go to crucial.com and use their memory selector to find out what kind of RAM to get. Then get the same specs from other manufacturers, if you so desire. When you get to this level of detail, your head eventually starts hurting.

Standard' RAM chips are organized a DEPTH x 8 Bits. E.g. 32x8, 64x8,
etc. That means 8 of the chips make up a 64 bit wide rank (memory bus
is 64 bits wide). "Double Sided" is an old term to describe a stick
with 16 chips, 8 on each side. And with DEPTH x 8 chips that makes for
2 ranks (or, again in an older style terminology: 2 'banks').

'High Density' chips are DEPTH x 4 bits so it takes 16 to make a 64
bit wide memory rank. And this is why "double sided" is no longer the
favored description because when x8 chips are used "Double sided"
means "double rank" but with x4 chips it takes both sides and 16 chips
to make the ONE, single, rank.

Now to the problem. A memory 'slot' is usually designed for 'standard'
x8 chips and memory sticks containing 2 ranks. That is how the
'capacity' will be described. I.E. the K7S5A says it can handle up to
"1 gig" with two DDR slots, and that means 512Meg per slot, which
means 256 Meg PER RANK. (2 ranks per slot, 2 slots, etc)

But a 'high density' memory stick crams the 512 Meg into ONE RANK by
using 16 deeper (twice as deep) x4 bit width chips. And this is how
they arrive at the confusing term 'high density'. The chips themselves
are no higher in density than the x8 chips but since they are
organized as x4 they can cram more 'bytes' into a single rank because
16 chips make up a rank rather than 8, not that it helps make the
stick itself any 'higher' in 'density' because you can still only get
16 chips mounted on the thing.

So, a 512 Meg 'high density' stick puts 512 Meg in ONE RANK and a
'standard' density 512 Meg stick is two 256 Meg Ranks. Same size, same
'density'. It's the RANK organization that's different.

Since the memory slot on a K7S5A is two 256 Meg Ranks, a standard
density 512 Meg stick will work but a 'high density' 512 Meg stick
will not.

However, a 'high density' 256 Meg stick probably will since it crams
the 256 Meg into ONE RANK and the K7S5A can handle 256 Meg ranks.

For example, I'm running SDRAM on my K7S5A and, as it turns out, one
is 'standard' x8 density and the other is 'high density x4. But
they're both 256 Meg sticks and they both work. Damn irritating,
however, as they were both bought at the same time inside the same
package label, and same part number, with 16 chips on each so they
look identical (Kingston) but they are NOT the same thing. Doesn't
matter to my K7S5A but it means I can not use the 'high density' one
in my other motherboards because they support 128 Meg ranks (256 Meg
per slot but NOT in 'high density').

So, in a nutshell, if you're looking for 512 Meg sticks, make sure the
spec says they use x8 chips. But, if you're not trying to get 1 gig
then two 256 meg 'high density' sticks will be cheaper.

 

[fainis]

great review nobly

 

[13thmonkey]

I hope this isn't breaking any rules, sorry if it is...

Heres a link to another forum, where many people were testing cheap High density Ram, and somewhere in there they have started to devleop lists of compatible chipsets for high density Ram. I myself was looking at it as it was very cheap, but Nforce2 Mobo's won't take it, not sure about newer chipsets. The prices were very tempting, about $50/Gb, but looking at this it really wasn't worth the risk.

It backs up Nobly's comments.

http://www.hardforum.com/showthread.php?t=936638&page=1&pp=20

 

[nobly]

great review nobly

Thanks, but remember I just copied/pasted it. I just read it before I posted it to make sure the guy knew what he was talking about.