bymyfault said:
why was the architectural need to make ram sockets, concretely 3rd and
4th socket just for SS modules(against DS in 1st and 2nd sockets), the
same for dual channels for 4 modules or just for two modules in 3rd
and 4th socket, they have to be SS modules.
why would manufacturer in 2003.(K7 Triton series, GA-7N400) had a need
to make such an adjustment ?
Nforce2 controls a maximum of six ranks of memory.
On my Asus motherboard, that would correspond to three DIMM slots,
each of which is double sided, for a total of six ranks of memory.
Cnannel0 Channel1
Slot 1 Slot 2
(DS) (DS)
Slot 3
(DS)
Nforce2 has three address controllers, one driving each slot.
(This is wasteful of pins on the Northbridge, but allows lower
drive current to try to reduce simultaneous switching noise.)
It has two data busses, one for Channel0 and one for Channel1.
Now, say a manufacturer wants to make a "four slot" motherboard.
The simplest way to do that, and maintain the six rank limit, is
like this.
Cnannel0 Channel1
Slot 1 Slot 2
(SS) (DS)
Slot 3 Slot 4
(SS) (DS)
In terms of supporting a dense memory solution, this is useless.
Adding "SS" slots is a waste of time. Better to just make
a three slot motherboard, all slots DS.
For the maintenance of a dual channel configuration, you set
up a three DS slot board like this. This gives 2GB total, and
works fine. Bandwidth is consistent from top to bottom of
the address space.
Cnannel0 Channel1
1GB 512MB
(DS) (DS)
512MB
(DS)
This puts equal quantities of memory on each channel, such that
the controller can alternate between Channel0 and Channel1 while
ascending through the memory space.
If I were to take the 1GB (DS) module, and make two 512MB (SS)
modules with it, I could use the four slot board like this.
Cnannel0 Channel1
512MB 512MB
(SS) (DS) <------ could actual be DS or SS if you want
512MB 512MB
(SS) (DS) <------ could actual be DS or SS if you want
The four slot motherboard gave no net gain for the user. Just
a nuisance, looking for (SS) modules. The motherboard
"looks pretty", which is why they did it. It has no technical
justification.
If you try this for Nforce2, there are reports it doesn't work.
The free memory seems to stop at 2GB. Adding any more memory
above 2GB will be rejected, for unknown reasons. I haven't tried
this, but it's just possible the motherboard won't even pass POST.
Cnannel0 Channel1
1GB 1GB
(DS) (DS)
1GB
(DS)
The unbalanced memory configuration itself, works fine. I've tested
and characterized this configuration.
Cnannel0 Channel1
512MB 512MB
(DS) (DS)
512MB
(DS)
From location 0 to the 1GB mark, the memory bandwidth is perhaps
1400MB/sec, while from 1GB to the 1.5GB mark, the memory bandwidth
drops to around 900MB/sec. This means, the lower two thirds of
address space is running in dual channel mode, while the upper
third runs in single channel mode. Your program may run slightly
slower, if it is loaded into memory in the upper third (above 1GB).
That is some Nforce2 trivia.
Paul
