Running 3 or more Dimms (DoubleSided) on a S754 or S939 board?

[DreamKaZz]

I'm shopping for the AMD64 System, currently worried about the memory configs of the AMD64 Boards.

I heard that most of the AMD64 boards can only run with 4 dimm banks, so 1 Stick of 512 DoubleSided RAM would take 2 banks, so having 3 x 512 (DS) DIMM would take 6 banks so the 3rd dimm will be disabled or run at very low speed ex: like a DDR400 stick running @ PC1600.

Is that with all S754 and S939 boards?

Is that an old problem now fixed.

I have my eye those boards atm.

MSI K8N Neo Plat.
DFI Lanparty UT
Asus K8N-E

I plan on running 1.5GB of ram.

 

[Peter]

Your theory is a nice mash of what once were the right facts

Socket-754 usually implements three DIMM sockets. All three are fully operational, with single- or double-sided DIMMs. Socket-939 uses a 2x2 DIMM setup, while socket-940 with its registered DIMM strategy allows up to 2x4 DIMMs per CPU.

The thing to watch out for on 754 and 939 is electrical load. Remember, PC3200 operation is specified and guaranteed for ONE single DIMM (per channel, of course); YMMV on whether or not you will achieve stable 200 MHz operation with two DIMMs on each channel, let alone three. The board may have to step back to PC2700 speed with two DIMMs on each channel, and to PC2100 with three. Again, that's how things are specified by the JEDEC comittee - one DIMM for PC3200, two for PC2700, three for PC2100.

So, if you want 1.5 GBytes of RAM, your best bet is to go with socket-939 and use a twin set of 1-GByte DIMMs. That's one double-sided DIMM per channel then, a safe bet for PC3200 operation.

 

[cryptonomicon]

it's interesting. in the dfi nf3 manual it declares that using over one slot of double-sided pc3200 will make the chipset(?) default back to 166mhz speed (333mhz eff).


However... then on the very next line it says you can 'manually adjust' it back to 200mhz in the bios.

 

[Peter]

Exactly that's what this is about. No more than one DIMM for PC3200. Per channel - so if you have a socket-939 system there, you can have one DIMM on each of your two channels and still run PC3200 (200 MHz).

Properly written, standard-compliant BIOS will decrease RAM clock speed with increasing load; the user is free to override that and do as they please - at their own risk.

 

[DreamKaZz]

Are there any motherboard that handle 3 or 4 DS Ram @ DDR400 better than others? Like the MSI Neo2 Plat S939?

I just cant afford 2 x 1GB sticks atm.

 

[Peter]

If you want to be safe with lots of DIMMs, you need to go with Registered type DIMMs and socket 940. Ain't no such thing as a free lunch.

You can make a half-safe cheap bet with a twin set of single-sided 512-MByte DIMMs on socket 939. That'll leave you with half a chance of adding another twin set of the same later.

But even if you have to step back to PC2700 (166 MHz) then, the performance loss isn't that big. This isn't the Pentium-4 ... AMD's processors are much more efficient in using their caches and buffers; RAM speed isn't that important here.

 

[DreamKaZz]

I've checked the MSI K8N Neo manual the lastest version, it says you can run dimm 1 2 3 with DS ram @ DDR400.

 

[DreamKaZz]

Thank you peter, alot of good info here.

 

[DreamKaZz]

Another question is it worth getting low timing RAM, does it make a big difference?

 

[Shimmishim]

if you are trying to squeeze out the last bit of performance, then yes, low timing RAM would make a difference...

but for the casual user... probably not at all...