Memory Devider Info

[curtisbouvier]

Can someone please teach me as to what this does.

It takes the speed of 400 and changes it to 333/266/133 correct?

Doesnt that sightly defeat the purpose of overclocking or am i missing somthing?

If you could show me mathematically...

DEFAULT is 12x200 = 2.4ghz

using a memory devider would then be 12x333 or 12x266??????

how exactly does this work?

 

[Rhagz]

If you wanted to overclock the CPU without pushing the memory past its limits, then you use a divider. This is especially useful when trying to keep tight timings on your ram. Most ram will perform better with lower latency at a lower bus speed then it would with loose timings at higher speeds. So you take your 12x200 and pump it up to say 12x250 and get 3.0Ghz cpu and run a 5:4 divider and your memory still runs at its standard 200Mhz. I think this is right, feel free to correct me if I r rong!

The divider simply reduces the FSB (HTT) speed. If your FSB is 250, then a 5:4 divider would reduce your memory speed by 4/5. 4x250=1000/5=200 memory speed. There is your math!

 

[Navid]

A system is often limited by one component (bottleneck).
In a scenario, you may have a CPU that can overclock really well. However, you may have a standrad memory. As a result, your memory may be the bottleneck and may limit the overclock substantially. If you want to allow your CPU to overclock, one option you have is to set your memory to run at a divider. So, let's say you set it to run at mem:CPU = 4:5. Then, at default rate, your memory will be underclocked while your CPU will be at the default rate. Then, you can increase FSB and when your memory reaches its default rate, your CPU will be overclocked by 5/4 or by 25%.

This was just an example. It may turn out that if you set to that ratio, your bottleneck will change to your CPU. It may turn out that when you reach the maximum FSB< your memory is still underclocked. Then, you have to try both cases and find out which one gives you a better system overall.

 

[Concillian]

You can learn a LOT about how memory dividers impact performance by looking at one of the AT RAM testing charts like this one:

http://www.anandtech.com/memor...c.aspx?i=2215&amp;p=13

Look at the performance difference between 200 MHz @ 2-3-3- and 267@3-3-3 with the same overall CPU speed. Performance improvement is only about 4% for Q3 (known to be very memory timing critical) and ~3% for Wolfenstein: ET (built off the Q3 engine). So in an extreme case performance improvement is 3-4% in games by raising from 200 to 266 MHz.

On that same chart they have an example at 273 MHz memory (a small change from 266) but the CPU is running just 60 MHz faster at 2460 instead of 2400. That change yielded ~2.5% improvement in both Quake3 and Wolfenstein:ET. if you got 3% performance from bringing memory from 200 MHz to 266, you're not going to get much by adding only 7 MHz, so most of that 2.5% has to be from a clock speed increase of ... 2.5%
Is it coincidence that the clock speed increase was the same as the performance improvment?

Bottom line is that, in general, CPU MHz is significantly more important than memory speed, at least with the A64. So a divider hurts you, but not a ton.

If you are going to use a divider, it's also important to understand how the A64 deals with memory speeds. Because the memory controller is on-die and running at CPU speed, the A64 will only run memory speeds that are an integer divided by the CPU speed. This keeps memory signals completely in sync with the memory controller. As such, memory may actually run SLOWER than you get by using the divider. This is especially true of using half multipliers.

Example: 8.5 * 280 = 2380 MHz
but if you set memory at 1:1 you're actually going to run your RAM at 2380 / 9 = 264
since 8.5 isn't an integer, it will divide by the next higher integer (9)

In the same example if you run 5:6, you may think you'd get 280 * 5 / 6 = 233.3 MHz, but you can't get that from 2380 divided by an integer. The actual RAM speed will be 2380 / 11 = 216 MHz, significantly lower than what you would think from the divider.

For people who have memory from their AXP or P4 system, it's often the best decision to just keep that memory and use it a little slower with a divider, rather than going out and spending $300 on memory that can run 1:1 speeds. As the small performance gain just isn't worth the investment to most people. Even to those buying a new system, Value RAM is like half the cost of RAM that could run 1:1, and that is a significant cost of the overall system for only a small performance gain.

 

[curtisbouvier]

Wow this is some haul ass info guys i appreciate it. I'm printing all your posts so i can bring to work and read about it. for now

before i leave i will ask you guys. What ram do you reccomend i buy for the best performance in overclocking? with the DFI board and the A64 3400 cpu..

back in 8 hours haah =)

 

[curtisbouvier]

so this is the impression i am getting

Playing with the memory timings will give me a 10-15% speed increase. memory deviders and so forth.

Buying PC4000 ram (ballistix) and running 12x235 instead of default 12x200 for a whopping 2.82 ghz in that area. 400 mhz overclock will give me alot more than 10% speed increase correct? the ram is PC4000 so the timings will NOT change unless i go over ddr500 speeds correct?
so thats pretty much what it boils down to i think.

 

[Rhagz]

I would personally reccomend the OCZ 2x512 Platinum Rev 2. It's 2-2-2-5 timings at 400, and can overclock without adujusting them too much. They are reliable to DDR580 speeds with enough voltage, and it is possible to get DDR600 out of them with a 2T command rate, but performance is a little under 580 at 1T. Other memory is good too, there is a lot of good stuff out there.