Odd divisor correct and what it does.

[Tony]

Guys

Odd divisor correct acts pretty much like a down clock ratio dependant on the CPU multi and the ram ratio you are running. You can with a 9 or other odd cpu multi think you are running 300fsb 1:1 when in fact your ram is running a lot lower.
Issue is no benching programs read your ram speed correctly when you have this option enabled as they don't take the registers it sets into account.You can only see a change in bandwidth measured.

I asked Ryder to comment on how to work the actual ram speed out as he has a nice clear way of explaining how this all works.

Over to you Rydeeee

[RyderOCZ]

Further info on Odd Divisor Correct:

This function always rounds your Ram divider to an even number, so if you are running 1:1 with an Odd CPU multi, your ram will run slower than the FSB (very similar to the 0.5 multiplier's)

Example: 250 FSB x 11 CPU multi at 1:1 = 2750 CPU speed / 11 = 250 Ram speed (DDR500)
If you enabled Odd Divisor Correct, your Ram divider would be 12 which would put your ram at 229.167 in this example.


Example #2: 330 x 9 at 5:6 (166 memclock) = 2970 CPU speed / 11 = 270 Ram speed.
Enable Odd Divisor Correct and your divider will go to 12 and the ram speed would be 247.5 MHz.

Software - CPU-z, Memtest, Everest, etc will not identify that your ram is running slower. The only way that I have been able to demonstrate it, is with memtest and comparing the measured bandwidth (I will try to confirm in Sandra as well and post some screen shots shortly.)

Now the exception (sort of) to this rule is when you have an odd CPU multi and your divider already comes out to an even number, Odd Divisor Correct will have no effect because there is nothing to "correct".

This can be very beneficial when you are trying to push the CPU that little bit farther, but your ram is holding you back.
We have also noticed that when you are running the "Upclock" ram ratio's with the "E" Die CPU's it will give you "something in between" the given ratio's

[ozzimark]

i understand, but if it's possible to do that, why not just go all out and let us directly select the memory divider?

also, i'm trying to figure out a scenario where this is actually beneficial. seems that the overall effect is similar to trying to run at 1/2 cpu multi when at 1:1 ratio

[dinos22]

ok but where is this Odd Divisor Correct option kinda lost me there

[Tony]

In the 406 bios files i released is where you will find it, it is also on the CFX3200 bios.

Its actually good if you are using the 250 ratio as it seems to drop you down a little below the 250 but above the 233. Benching a CPU at 200 to 240fsb is usually a lot easier on the CPU but you usually lose ram speed, this may give you an option to gain some back with an added upclock ratio.

[dinos22]

In the 406 bios files i released is where you will find it, it is also on the CFX3200 bios.

Its actually good if you are using the 250 ratio as it seems to drop you down a little below the 250 but above the 233. Benching a CPU at 200 to 240fsb is usually a lot easier on the CPU but you usually lose ram speed, this may give you an option to gain some back with an added upclock ratio.

so will i FINALLY get 13/RAM RATIO with this option.........if so i am flashing my UltraD benching rig right now

[RyderOCZ]

so will i FINALLY get 13/RAM RATIO with this option.........if so i am flashing my UltraD benching rig right now

No.......Odd Divisor correct will only give Even numbers....It corrects the Odd Divisor to Even

[RyderOCZ]

Screenshots I promised of Sandra

Odd Divisor Correct Enabled:



Odd Divisor Correct Disabled:



As you can see, memory speed and CPU speed look exactly the same but the bandwidth is significantly lower with the ODC enabled because my ram was on a 12 divider instead of 11.

[ozzimark]

nice memory benches. about what i found to be true as well, though i looked at 333x9 at 1:1 with it enabled and 300x10 with it disabled, about the same

Its actually good if you are using the 250 ratio as it seems to drop you down a little below the 250 but above the 233. Benching a CPU at 200 to 240fsb is usually a lot easier on the CPU but you usually lose ram speed, this may give you an option to gain some back with an added upclock ratio.

yeah, i can see that now... though inbetween 250 and 233, shouldn't it be possible to just use 233 and use a 1/2 multi lower than what was set? while this won't apply to every case, it's a possibility.

however, i just did some math.. unless the ratios aren't what they should be (5:4 and 7:6 for 250 and 233), then there is never a time when there's more than 1 between memory divider set by the two respective ratios from a range of multipliers between 6x and 15x, including the 1/2 multi's.


the difference..

disabled

	  4/5 	  6/7 	 12/13	1      
15	12	13	14	15
14.5	12	13	14	15
14	12	12	13	14
13.5	11	12	13	14
13	11	12	12	13
12.5	10	11	12	13
12	10	11	12	12
11.5	10	10	11	12
11	9	10	11	11
10.5	9	9	10	11
10	8	9	10	10
9.5	8	9	9	10
9	8	8	9	9
8.5	7	8	8	9
8	7	7	8	8
7.5	6	7	7	8
7	6	6	7	7
6.5	6	6	6	7
6	5	6	6	6

enabled

	  4/5 	  6/7 	 12/13	1      
15	12	13	14	16
14.5	12	13	14	16
14	12	12	14	14
13.5	12	12	14	14
13	12	12	12	14
12.5	10	12	12	14
12	10	12	12	12
11.5	10	10	12	12
11	10	10	12	12
10.5	10	10	10	12
10	8	10	10	10
9.5	8	10	10	10
9	8	8	10	10
8.5	8	8	8	10
8	8	8	8	8
7.5	6	8	8	8
7	6	6	8	8
6.5	6	6	6	8
6	6	6	6	6

12:13 is for the 216mhz ratio, even though dfi claims it to be.... 10:11?

[RyderOCZ]

@Ozzi,

When ODC is enabled your math may come up with an odd divider...but it will round up to even...so in your second chart...all the 13's would be 14

[afireinside]

I'm a bit confused here. With my expert running 11/17 BIOS which doesn't have odd divisor and I run 300*9 with a 200mhz ram ratio (/9 divider) is my ram running at 300mhz or not?

[RyderOCZ]

I'm a bit confused here. With my expert running 11/17 BIOS which doesn't have odd divisor and I run 300*9 with a 200mhz ram ratio (/9 divider) is my ram running at 300mhz or not?

Yes, if you don't have ODC...then it can't and does not effect your ram speed at all.

[bachus_anonym]

I don't quite understand the purpose of it besides being beneficial in very rare cases - div233 < mem < div250...

E.g. 330x9 div166 & ODC Enabled is nothing else but 330x9 div150... or 270x11 div200 & ODC Enabled is also nothing else but 270x11 div183 (we know it's CPU/12 not CPU/13)

How is it better? Or am I missing something here...

EDIT: I just realized something - this is a PERFECT cheat! Enabled EDC in BIOS, no soft detects it and let's wait for peeps to start discovering how their RAM clocks like crazy Funny, but a bit sad at the same time

EDIT2:... provided that dividers are not used an done is using odd multi, that is

[ozzimark]

@Ozzi,

When ODC is enabled your math may come up with an odd divider...but it will round up to even...so in your second chart...all the 13's would be 14

yup, which is what i did. in reality though, it does about the same thing as lowering the ratio one step (or two in some cases)

[RyderOCZ]

I don't quite understand the purpose of it besides being beneficial in very rare cases - div233 < mem < div250...

E.g. 330x9 div166 & ODC Enabled is nothing else but 330x9 div150... or 270x11 div200 & ODC Enabled is also nothing else but 270x11 div183 (we know it's CPU/12 not CPU/13)

How is it better? Or am I missing something here...

You are not missing anything.....but as you pointed out somewhere around here....some CPU's and Multi's don't allow the use of 150 mode...so it would be beneficial in that case.

This was not meant to say "you must use this and you will love it" more like it is another method to tweak your ram to your advantage. This option replaced the Write Cas Latency in the bios which didn't do anything for anyone because only a value of 1 is valid on DDR1.

[ozzimark]

You are not missing anything.....but as you pointed out somewhere around here....some CPU's and Multi's don't allow the use of 150 mode...so it would be beneficial in that case.

aha, that's one that escaped my mind. so set to 166, and if it sets an odd cpu multi and you want your ram running slower, but 133mhz is too low.. enable!

[RyderOCZ]

aha, that's one that escaped my mind. so set to 166, and if it sets an odd cpu multi and you want your ram running slower, but 133mhz is too low.. enable!

Now you are catching on

[ozzimark]

Now you are catching on

i take it from the silence before about this that it's not possible to replace the ratios in the bios with actual memory dividers, like "cpu/5" all the way up to "cpu/50"?

[Tony]

From some playing here it all depends on your CPU HTT as to what this option will do, my initial request to Oskar was to give us something else to play with as write cas is useless as DDR1 only supports a write cas of 1, I had tested a little with the refernece ATI boards which have all the tweaking options and we did find ODC to have some uses.

Now there is another option called burst2opt, this again has limited uses but may prove better than ODC for most. If I can catch Oskar on a good day i will see if we can play with this option and release another batch of bios files to see if there is anything to gain.

[bachus_anonym]

It seems like ozzi and OPB got fooled a bit by this option in the other thread It could have been so beautiful

[masterofpuppets]

I don't really understand what is going on here. So I am guessing, if you have an odd memory divider, my RAM will be running slower than it's measured?

[RyderOCZ]

I don't really understand what is going on here. So I am guessing, if you have an odd memory divider, my RAM will be running slower than it's measured?

Your ram would only be running slower, if you had a bios with ODC in it (the 406 modded by Tony) AND had it enabled.

[masterofpuppets]

Your ram would only be running slower, if you had a bios with ODC in it (the 406 modded by Tony) AND had it enabled.

Ahh, so I guess this doesn't affect me

[ozzimark]

It could have been so beautiful

you said it

oh well. such is life

[STEvil]

I think on the sapphire boards previous to the 3200 series (ie: RD/RX 480) this option had the values "Update" and "Limit" but I cant recall the option.. its second one down in the memory options for my pure crossfire advantage.