AM2 multies and dividers

[TheGlasMan]

There is some confusion about the memory speeds of AM2 cpu's with ddr2. The basic method is the divider is divide the multi by 2, and increase to the next whole # if a fraction.
The divider for a 12 multi is 6, and the same for an 11 multi (5.5=6) This means that odd multies cannot run ddr2 800 at stock speeds

Here is a pretty complete list of memory speeds with HTT sttings with various dividers.
Stolen from http://www.xtremesystems.org/forums/...d.php?t=105798


This should make it easy to figure your memory speed with various overclocks.

Low multies appear to be a bit wacky.

[Peter M]

Why make it so complicated? Only two steps needed:

* RAM divider is a simple "best match" algorithm down from core speed.

* system frequency (falsely "HTT") overclocks proportionally overclock the RAM as well.

E.g. when you have a 2200 MHz CPU and DDR2-800 RAM (400 MHz), then you'll get a RAM divider of 2200/400=5.5. Round up to nearest integer, 6, hence 366 MHz RAM clock.

Push sysfreq to 220 MHz (up 10%), and have RAM run at 10% higher as well - 403 MHz.

[TheGlasMan]

What's complicated?

[Peter M]

the divider is divide the multi by 2, and increase to the next whole # if a fraction.

This is - and it works with DDR2-800 only. Most people with normal budgets will buy DDR2-667.

[TheGlasMan]

That's why I posted the chart. (Cause some people around here think dividing a number under 20 by 2 and adding one is complicated)

[CNT]

I am still not fully understanding all this, but I got a start though. I didn't know that I had to take the core CPU speed and divide it with RAM speed (half of DDR2), then use the chart to see where the RAM will run on. Seems best CPU would be either X2 3800+ (2.0GHz) or 4600+ (2.4GHz) to get even CPU multiplier number. I am getting there!?!?

Chuck

[Peter M]

Actual RAM frequency is always half of the DDR-xxx number, regardless of whether it's DDR or DDR2.

Now if you intend to use DDR2-800 RAM at 400 MHz, your ideal CPU is operating at a speed that is divisible by 400. With more mainstream DDR2-667 RAM at 366 MHz, few choices exactly use the RAM's speed potential. Not that the few missing MHz did much to actual application performance ...

[CNT]

FYI... I just install everything "as is" and did NOT change anything in the BIOS (no overclocking, no nothing). I am getting this:

(hardware/OS)
MSI K9N Platinum
AMD Athlon 64 X2 4200+ (2.2GHz)
2x1G Corsair XMS2 PC2-6400
MS Windows XP Pro x64 Edition

(BIOS)
Current CPU Clock: 2223 MHz
Current FSB Multiplier: 11x
Current Memory Speed: 800 MHz
CPU Voltage: 1.288 V (1.280~1.296)
Cool'n'Quiet: Disabled
Adjust CPU Voltage (V): Default
CPU Frequency (MHz): 200.0
CPU Dynamic Overclocking: Disabled

Memclock Mode: Auto
Adjust DDR Voltage (V): 1.90

PCIE Frequency (MHz): 100

I thought the RAM would be 533MHz since the CPU is 2.2GHz, but it's 800MHz (or does it mean 400MHz x 2?). This looks good, I didn't have to change anything to fully utilize the RAM (DDR2-800). It's multiplier is at 11x (not 7x), default. Or am I not understanding something?

Chuck

[PF Prophet]

Actual RAM frequency is always half of the DDR-xxx number, regardless of whether it's DDR or DDR2.

Now if you intend to use DDR2-800 RAM at 400 MHz, your ideal CPU is operating at a speed that is divisible by 400. With more mainstream DDR2-667 RAM at 366 MHz, few choices exactly use the RAM's speed potential. Not that the few missing MHz did much to actual application performance ...

also remmber ddr2 is mostly the same stuff just diffrent voltages and timings to get diffrent clocks, to truely use its potential you gotta volt up and test for best timings to clock ratio

took me 4 nights of tweaking to find my best balance, now im gonna try for max cpu clock again soon.

[TheGlasMan]

Run cpu-z in windows to confirm bus speeds. (some times the bios isn't too smart.)
as a note, s939 with e stepping (venice etc) cpu's had a 250 memory setting so htey could run 250 (ddr500) memory at default speeds. Maybe something like that in your bios. (don't see why not, just per above posts isn't known yet.)

Looking forward to your cpu-z results.

[CNT]

Looking forward to your cpu-z results.

You're right, it's 369 instead of 400. Maybe I need a BIOS update?

clock

Chuck

[mr_raider]

No. That's correct for a 4200. It will run at ddr2-733, or 366 each way.

[TheGlasMan]

You're right, it's 369 instead of 400. Maybe I need a BIOS update?
Chuck

Don't think so, they may fix the reading but nothing will change. Not to worry.

You're all set for overclocking though, or I would try lowering the timings to 4-4-4 as it will give better performance than 800 at 369 etc.

[~Morphed~]

marked to follow up .............or should i even care......... na wait till next fall...........

[Mr_Speedy]

For overclockers it doesn't matter what the default speed of the RAM is at stock settings, for all I care it could be 1MHz

My RAM is overclocked to the limit and is at its "full potential"

But nice of you to post this information, it clears some things up...