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Can someone explain LDT to me?

N

Nebben

Senior member
I have just finished building my new system and am reading as much as possible about overclocking before I try anything too extreme. Here's my question:

I have read and almost fully understand the guide at the top of this forum (Quick and dirty A64 OCing) but there's one aspect I'm not really knowledgeable of. What exactly is LDT? I understand the definition and effect of HTT, Clock multiplier, RAM dividers, etc. but am pretty much clueless about LDT.

Can someone give me a working definition of what LDT does and what impact it has on system performance?

Thanks
 
Basically, you need to keep your LTD x HTT at < 1000.

For instance if you are upping your HTT to 250 you'd need to drop your LTD from 5 to 4. It's set 200x5 by default.

Which motherboard are you using?
 
DFI LanParty UT NF4 Ultra-D
I've had the LTD settings on Auto up until now.

I'm finding through my testing that my RAM is basically my only real limitation (as was expected) but here's the other major question I have (copied from another forum)



Does the memory divider setting matter at all, or is only the actual RAM frequency in the end important?

I.E. Is RAM being clocked at 1:1 at 200 HT exactly the same performance-wise as 241 HTT with a memory divier of 166 (0.83 x 241 HTT = 200.03)

Because if these two are essentially the same, I should not be limited much at all by my value RAM, correct? Because I'm currently able to hit about 2.50GHZ and be stable in Prime95 and several games, with my RAM using a lower divider.

If there's a performance difference when using a divider, is it enough to warrant the cost of higher-quality RAM capable of high clock speeds? I'll most likely be using the value RAM for a while regardless, but in the future I'd like to know the best way to go.
 
Of course there is a performance difference between running the ram with a divider. Your value ram is holding you back and is the main drawback to cheaper ram. It may perform the same in your example, but you leave out the best scenario, ie; running the ram at 1:1 at 241. That is where the value ram kills you. It's become popular to post threads claiming that value ram is all that is needed in an AMD system. I think that got started by someone wanting to feel good about not having good ram in their system and they had no shortage of people willing to jump on that bandwagon. Any system, AMD or Intel will perform better with good ram that will run the best timings possible... granted the difference is smaller in an AMD system..... but it's still a difference. It all comes down to what you will accept in your system, if you are happy with the lower performing memory then it's fine, if you want your system to perform at it's highest possible level then get good ram.
 
Yes, it is motherboard specific. Some mobo's (like my AV8) call it LDT. Others will simply call it HTT multiplier. Either way, whatever your motherboard calls the CPU external frequency (FSB, HTT, etc.) x HTT/LDT/any others? should be kept at about 1000 or lower. Like somebody mentioned, even going to 2x doesn't hurt performance and sometimes helps.
 
Originally posted by: boshuter
Of course there is a performance difference between running the ram with a divider. Your value ram is holding you back and is the main drawback to cheaper ram. It may perform the same in your example, but you leave out the best scenario, ie; running the ram at 1:1 at 241. That is where the value ram kills you. It's become popular to post threads claiming that value ram is all that is needed in an AMD system. I think that got started by someone wanting to feel good about not having good ram in their system and they had no shortage of people willing to jump on that bandwagon. Any system, AMD or Intel will perform better with good ram that will run the best timings possible... granted the difference is smaller in an AMD system..... but it's still a difference. It all comes down to what you will accept in your system, if you are happy with the lower performing memory then it's fine, if you want your system to perform at it's highest possible level then get good ram.
Click to expand...

Well the thread that started this has proof to back up its claims. Zebo did multiple benchmarks with multiple configurations and the results were negligible at best. So where's your data to back up your claim that he needs more than value RAM? The point Zebo was making is that clockspeed > memory bandwidth. I'm running my value memory at DDR350 and that allows me to get a 550MHz overclock. I'll take a 500MHz overclock and a 50MHz decrease in memory speed any day. I gained more then I lost. No one said that the Athlon 64's don't run faster with fast memory, we're just saying that for some of us paying $100 more for a single digit performance increase over value memory isn't worth it. The FSB on chip means that the Athlon64 is less memory bandwidth bound than the P4's and K7's.
 
yup

Run your memory with a divider and crank up your CPU core speed. No performance loss should be noticed. Thats one of the benefits of the A64 memory controller.
 
Originally posted by: Traire
Run your memory with a divider and crank up your CPU core speed. No performance loss should be noticed. Thats one of the benefits of the A64 memory controller.
Click to expand...
So are you saying I would get better performance with CPU clock speed at 2.4GHz at DDR365 speeds than 2.2GHz at DDR400 speeds?

 
Originally posted by: Jotho
Originally posted by: Traire
Run your memory with a divider and crank up your CPU core speed. No performance loss should be noticed. Thats one of the benefits of the A64 memory controller.
Click to expand...
So are you saying I would get better performance with CPU clock speed at 2.4GHz at DDR365 speeds than 2.2GHz at DDR400 speeds?
Click to expand...

Well, that might be pushing it. You'd probably be about the same with a plus 10 percent on CPU and minus ten percent on memory. Why can't you run the CPU @ 2.4 and the Ram at 436? Most ram in my experience will get this high. Otherwise, many CPU's will go more than +10% in which case dropping the divider allows some major OC's.

For example, my ram is using the 4:6 ratio. My 1.8 GHz Winnie is running 2.7 stable (*except for 3d apps when the AGP lock is flakin' out. Then I have to go down to about 2.55). With that speed and memory ratio, my RAM is doing DDR400-right @ spec.
 
Yes, it is motherboard specific. Some mobo's (like my AV8) call it LDT. Others will simply call it HTT multiplier. Either way, whatever your motherboard calls the CPU external frequency (FSB, HTT, etc.) x HTT/LDT/any others? should be kept at about 1000 or lower. Like somebody mentioned, even going to 2x doesn't hurt performance and sometimes helps.
Click to expand...

Can you give me a little more information on what exactly this does? I know I need to keep it below 1000, but how does it affect performance? Would it be better to be slightly over (like around 1060) or significantly under (in the 800's)?

I'm playing around with memory dividers and am unsure how the LDT setting plays in.

 
Originally posted by: Amplifier
Basically, you need to keep your LTD x HTT at < 1000.

For instance if you are upping your HTT to 250 you'd need to drop your LTD from 5 to 4. It's set 200x5 by default.

Which motherboard are you using?
Click to expand...

i've ran my board at 1220 for 30 minutes of prime before i noticed and lowered it via ntune.
 
Originally posted by: Nebben
Yes, it is motherboard specific. Some mobo's (like my AV8) call it LDT. Others will simply call it HTT multiplier. Either way, whatever your motherboard calls the CPU external frequency (FSB, HTT, etc.) x HTT/LDT/any others? should be kept at about 1000 or lower. Like somebody mentioned, even going to 2x doesn't hurt performance and sometimes helps.
Click to expand...

Can you give me a little more information on what exactly this does? I know I need to keep it below 1000, but how does it affect performance? Would it be better to be slightly over (like around 1060) or significantly under (in the 800's)?

I'm playing around with memory dividers and am unsure how the LDT setting plays in.
Click to expand...

The HT frequency has never made any significant difference in performance. In the first generation of S754 boards, many favored the K8T800 chipset simply because the NF3 150 had only HT 3x (600 HT) support compared to VIA's 4x (800 HT). They both performed practically the same.

Just keep the total HT frequency at a safe level and you shouldn't need to worry.
 
Originally posted by: Jotho
Originally posted by: Traire
Run your memory with a divider and crank up your CPU core speed. No performance loss should be noticed. Thats one of the benefits of the A64 memory controller.
Click to expand...
So are you saying I would get better performance with CPU clock speed at 2.4GHz at DDR365 speeds than 2.2GHz at DDR400 speeds?
Click to expand...

Yes. You'd have to lower the ram speed much more than that for it to cancel out a 200mhz OC.
 
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