using half multiplier = bad?

D

dr.kevin

2[H]4U
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Feb 17, 2006
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I remember reading a line about not using a half multiplier on a64 chips.

is it really bad? I don't understand the logic.

a half multiplier would help me get my cpu fast enough, but allow me to tweak the fsb and leave my ram and hypertransport as close to spec as possible.

my cpu can reach 2500mhz no problem. but my pc3200 ram, despite being 2-3-2-5, can't overclock for shit at these timings.. I just wanna keep it at an effective 400mhz.
 
meh

I used a half multi previously on my asrock without problems.

I think the biggest reason they reccomend against it, is it can be very difficult to determine the actual ram speed
 
BigTaf said:
meh

I used a half multi previously on my asrock without problems.

I think the biggest reason they reccomend against it, is it can be very difficult to determine the actual ram speed
Click to expand...

ah yes. this was the part i didn't understand.

how can you not know the actual ram speed when it is based on the fsb?

If my fsb is 220, my ram is ddr440, regardless whether my multiplier is 9x or 8.5x.

isn't this so?
 
I'm pretty sure that Athlon64 divides the cpu clock to get the memory clock. Not the system clock.
 
No, RAM is based off the FSB, I think half-multipliers lower performance, I could be wrong though.
 
dr.kevin said:
ah yes. this was the part i didn't understand.

how can you not know the actual ram speed when it is based on the fsb?

If my fsb is 220, my ram is ddr440, regardless whether my multiplier is 9x or 8.5x.

isn't this so?
Click to expand...
On K8 CPU's, the Memory Controller is on the cpu die, and operates at CPU mhz. Because of this, one cannot simply make a ratio between the HTT/FSB and Memory speed, but instead, there is an INTEGER DIVIDER from the CPU mhz that sets the ram clock. This divider is calculated with the DRAM Frequency Set option and the CPU Multiplier.
To find this divider, one must take the ratio selected and divide it into the CPU Multiplier.
Example:
CPU Multi = 9x
DRAM Frequency = 166mhz (5:6)
HTT/FSB = 320mhz

the CPU speed would be 2880mhz.
Now, the important part: How to Calculate the Memory Divider
Memory mhz = CPU Clock / round up(CPU Multiplier/Memory Divider)
So, that would be:
Memory mhz = 2880mhz / round up( 9 / 5/6 )
9 / 5/6 = 10.8. rounded up, this is 11
so now we have 2880mhz / 11 = 261.8mhz for the final Memory mhz.
 
so there is no confirmation that half multipliers are bad.....

it's all conjecture eh
 
the "bad" thing about it is that the ram isn't running at the speed you want it to, but it's easy to calculate that speed ;)
 
(cf)Eclipse said:
the "bad" thing about it is that the ram isn't running at the speed you want it to, but it's easy to calculate that speed ;)
Click to expand...

the same could be said for chaning the ram dividers then.

Dr Kevin

bottom line is I beleive ocing is about trying to maximize your performance, meaning do whatever works best for your components :D and never be afraid to try something, the internet for all the good it does, helps spread more rumors then anything else. Definitly pay attention to what eclipse sais though, ive never seen someone dedicate so much time to making sure other people understand the way a64s ram dividers work and he is 100% right.

Just dont let him touch your cpu he has a bad habit of breaking them :p
 
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