RAM:FSB - This has been bugging me...

furnace

furnace

furnace

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This has been bugging me, it just sounds wrong and could get me into problems when I start overclocking this xmas with my new rig. So I better try and understand my misunderstanding... lol :D

So I'm getting DDR2 memory, 800Mhz PC2-6400 (I guess it's CL5/5-5-5-12 as it's only Kingston and not particularly expensive).

But as its DDR2, that runs at 200Mhz in reality, right? x2 for DDR, then x2 again for DDR2..? So it's 200Mhz but 800Mhz "effective"?

I've read that FSB:RAM at 1:1 is best, but not always possible... But surely if you have, for example, clocked at 450 x 7 then your FSB is 450Mhz, yeah?

So my brain is telling me that to have FSB:RAM at 1:1, and your CPU running at 450 x 7, your ram would be running at 1.8Ghz?! As that's your FSB, x2 for DDR, x2 again for DDR2?

So even to get it down to 900Mhz you'd have to have FSB:RAM at 2:1, which is a huge bottleneck is it not?

I could me getting a number of things wrong here; the FSB and RAM relationship, the FSB:RAM ratio and bottlenecks, the way I'm pretty much saying DDR2 is FSBx4 ... I could be completely wrong, but I just need someone to clear it up for me and tell me what I've got mixed up?

I've read loads of tutorials and this is the only thing that seems to be confusing me regarding overclocking. Maybe I've read too many tutorials and have confused myself somewhere along the lines ;) Thanks
 
You're thinking too much heh

The pc6400 runs at 800Mhz at stock. That's 400Mhz doubled to 800Mhz as it's Double Data Rate.

A Conroe would need to be running on a 400 FSB to be running at 1:1 with the RAM at the RAMs stock speed.
 
well you close :D

you put in one to many x2's

its only doubled to make ddr2 800

soo if you had the 450mhz fsb like you mentioned. you first aply the ratio so at 1:1 would be 450 still then double it so ram would be running at 900mhz

for instance my pc has 330fsb with a 4:5 ratio means 412.5mhz doubled to make 825fsb ddr2
 
Ahh I see..!

*feels less confused now*

So the RAM will be running at 400Mhz...

Is most RAM easily overclockable? The only specs I've got for my ram is:

Kingston 1GB DDR2 SDRAM Memory Module 800MHz DDR2-800/PC2-6400
@ £90 ex VAT (this is probably trade price plus a few pounds or so, the guy's doing me a favour. Maybe this is worth £110 inc vat and store profit, if that gives you any indication of what ram it might be).

I know you can't tell much from that so I'll probably be asking better questions when I actually have it & its packaging in front of me, but do you think that'll run at 450Mhz (900Mhz) without dying on me? I have RAM sinks on an old computer, but I always wonder if they do anything... always look to me as if they're just gonna hold the heat in :-P But I can't afford to burn RAM. I spent all my money buying it once, forget about replacing burnt bits hehe :D

Thanks for pointing me in the right direction there :cool:
 
I wouldn't think the 5-5-5-15 would clock too high. Tho 450 isn't all that high. You may need to loosen the timings slightly to get to 450.
 
Cob said:
I wouldn't think the 5-5-5-15 would clock too high. Tho 450 isn't all that high. You may need to loosen the timings slightly to get to 450.
Click to expand...
Shame :( What do you mean by loosen the timings?
 
To say 5-6-5-15 or 5-5-6-15 or whatever.

But I've no experience of that particular RAM.
 
(If I come up with another question after this one, I'll go into the memory forums as it's getting a little memory specific ;))

How and why does loosening the timings allow for a higher FSB? I haven't come across that before
 
Most ram has a certain degree of overclockability but in order to get more MHz out of it, you usually have slacken the timings from their defaults and give it a bit more voltage. If your ram is rated to work at 400MHz, you could get it to run at 450MHz for instance by doing the aforementioned.
 
It's purely called DDR2 because it's second-generation/an improvement on DDR1, the name doesn't affect the speed :) Sounds like you know what you're doing otherwise!

furnace said:
How and why does loosening the timings allow for a higher FSB? I haven't come across that before
Click to expand...

By increasing the FSB, you're increasing the speed at which the components of the RAM must operate. Loosening the timings introduces longer delays into the process of reading and writing to RAM, so it gives you more breathing space to overclock the RAM/FSB.
 
( Decided to keep this in the overclocking forum :) if it needs moving to the Memory one, then feel free :D I won't moan! )

So 5-5-5-15, if I increased the latency to 5-5-6-15 or 5-6-5-15, would that affect the performance?

By doing that (changing from 5 to 6), I'd be pretty much forcing the RAM to take a longer break between selecting rows in the memory?

Will my RAM perform worse like that, or would the +50Mhz clock compensate for the extra latency?
 
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Figured I'd rather dig up this thread than start a new one on a pretty similar thing :)

Kingston HyperX - 1 GB DIMM 240-pin - DDR II 800 MHz / PC2-6400 - 1.95 V - unbuffered - non-ECC CL4

The guy I'm getting my parts from contacted me and said that's available for the same price as the CL5 I was getting, seeings it's CL4 I'd be better off with that.

Do you think it'll clock any better? You think I'd be able to push it to 450Mhz without burning it out? You rekon I'd still be best off loosening it to 4-4-5-12 or so?

(bit of a noob at memory clocking :p)
 
Yeah the CL4 stuff will be able to clock further, because the CL5 ram starts at CL5 when you loosen the timings you are going upto CL6, butt with the other RAM when you loosen timings you re going upto CL5 but at a higher speed than the first set, Sorry if this is confusing lol.

First set might do: 450MHz @CL5
Second Set might do: 450MHz @CL4

If you go higher on both sets and have to increase latencies the second set will go futher before you hit CL6.

Sorry if its confusing someone with more knowledge might be able to clear things up better.

Ben
 
Actually the individual IC's in DDR2 800 ram ARE running at 1/4 of the overall clockspeed.
The IC's in the modules run in pairs, kinda like dual channel ram does in a normal mobo.
So you've got 2 IC's running together at 200mhz which = 400mhz effective, which equates to 800mhz DDR.
Since the 400mhz is the external speed, thats the only number you really need to worry about.
 
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