Memory Command Rate - Motherboard or CPU?

[SunnyD]

I'm trying to figure this out - is the command rate of DDR handled/determined by the CPU or the Motherboard?

Not the setting, but the determination of how many DIMMs at what command rate.

 

[dunkster]

It can be either motherboard (BIOS) or CPU on-board memory controller.

Using 4 single-sided RAM sticks or 2 double-sided RAM sticks, the CPU memory controller will probably demand 2T command rate.

When you open your BIOS, you'll see a lot of optional timings/settings - but many OTHER timings/settings are hidden from you and beyond your control. Some of those hidden settings may prevent stable operation at 1T command rate.

Those hidden BIOS timings are often the real problem behind some RAM 'incompatability' with a particular motherboard.

Memtest86 Test#8 is the best test I've found to determine system stability at 1T Command Rate.

Hope this helps!

 

[Peter]

The rules are precalculated in the JEDEC provided standards of the various DIMM speed grades, fine tuned by whoever made the chip that contains the RAM controller (chipset or AMD64 CPU), tried and tested (hopefully) by the mainboard's designers, and then coded into BIOS.

 

[SunnyD]

Originally posted by: Peter
The rules are precalculated in the JEDEC provided standards of the various DIMM speed grades, fine tuned by whoever made the chip that contains the RAM controller (chipset or AMD64 CPU), tried and tested (hopefully) by the mainboard's designers, and then coded into BIOS.

Ah, so basically noone knows. 🙂

 

[Peter]

Yes. Everyone in that chain knows precisely what they're doing (ideally), so that in the end result the user plugs a DIMM and the system works - properly, and at its best speed. It is that balance that makes the art.

 

[Steve]

Originally posted by: SunnyD
I'm trying to figure this out - is the command rate of DDR handled/determined by the CPU or the Motherboard?

Not the setting, but the determination of how many DIMMs at what command rate.

It really depends on where the RAM controller is located. For Intel systems it's in the chipset. For AMD64 systems it's in the CPU itself.

 

[forumposter32]

If you know which motherboard and CPU you want to have, then can you determine which type of RAM to get to allow for 1T timing? I mean, I ordered an Athlon 64 3700+ (socket 754 Clawhammer) and would like to order an Asus K8N4-E Deluxe once I move. And I'd like to get OCZ Platinum 2x1GB but I'm thinking maybe only 1x1GB if I can't get 1T timing with 2 sticks. (I like UT2004 but only BF2 occasionally).

 

[Andres3605]

my old Msi Neo plat usde to run 2 double sided sticks at 1t, with a Newcastle 3000+

 

[Peter]

Like I said ... it's a chain of facts.

The generic JEDEC rule says 200 MHz with one DIMM (per channel only), two-DIMM operation demands 166 MHz operation. AMD's latest RAM controller update in the AMD64 processors stretches that to the possibility of 200 MHz 2T _if_ the DIMMs are really good and the mainboard design is near-perfect. Individuals may still achieve 200 MHz 1T in their much narrower environmental parameters. (Remember that everything someone _specifies_ has to operate _perfectly_ across the entire spectrum of temperature and voltage fluctuations. Narrowing those windows gives more headroom.)

Now, how to choose RAM? First of all, be aware that you can't EXPECT better than JEDEC specified operation. Be happy and bare a grin if it does, but don't expect it. Next, the fewer DIMMs and then the fewer RAM chips you put onto each channel's common bus, the better for signal integrity.

In other words, choose big DIMMs over many DIMMs, and _then_ choose single-sided DIMMs over double-sided ones.