How do I Decrease Latency?

[Gregedit]

Hi there.

I have been researching motherboards and memory to build a new PC. I have decided to go for the MSI 648 Max with the SIS chipset. I was planing on using 2x 256MB DDR400 memory chips but now I'm not too sure about it. This is really messing my mind up.

If i have a Processor that is running at 533 FSB and use DDR 400 memory, would I decrease latency by using DDR 266 which is 50% of 533 or should i rather use DDR 400 with a processor that has an FSB of 400.

But... to confuse me even more I have just read a post that says DDR 400 runs at 200Mhz FSB and DDR 266 runs at 133Mhz FSB. So based on that is "Processor 400 FSB with DDR 400" the better combination to decrease latency?

What is the fastest bandwidth combination with less latency?

Please help me stay sane.

 

[bum_jcrules]

"If i have a Processor that is running at 533 FSB and use DDR 400 memory, would I decrease latency by using DDR 266 which is 50% of 533 or should i rather use DDR 400 with a processor that has an FSB of 400."

Use the 4 way 133MHz FSB. (533MHZ effective FSB)

"But... to confuse me even more I have just read a post that says DDR 400 runs at 200Mhz FSB and DDR 266 runs at 133Mhz FSB. So based on that is "Processor 400 FSB with DDR 400" the better combination to decrease latency?"

For starters you are crossing CPU technologies. The AMD Athlon CPU uses a 2 way 133MHz FBS. (266MHz Effective FSB)

The Intel P4 uses a 4 way 133MHz FSB. (533 Effective FSB)

That aside I think you need to know how the CPU, the FSB, the Memory Bus and the Memory Modules themselves work together.

I will start by using the example of the CPU sending data to the memory modules. The CPU which is running at some multiple of the system clock frequency. System clock for a P4 which is what you are using would be at 133MHz. Notice that this is the base clock for the FSB. The data is sent via a signal from the CPU through the FSB to the Northbridge. (Large chip on you motherboard. The SIS chip in your setup.) The Northbridge contains something called the MCH. (Memory Controller Hub) This is where the speed differences between the FSB and the memory bus get syncronized. (This is sort of transmission between the engine, CPU, and the wheels, the memory modules.) The MCH uses the base signal of the system clock and uses a ratio to make the two work together. Now the MCH uses its own clock generator for the memory bus to use a signal that runs at the ratio determined so the two run in conjunction with each other.

Again from the CPU... CPU to FSB, FSB to Memory Contorler/chipset, MCH to memory bus, memory bus to memory modules.

As you can see, both can run at different speeds. You want to run both the memory and the FSB at the fastest signals possible. The best configuration is for the FSB to be at the same effective speed of the memory bus.

Sorry if this is not the best explination but I think you will get the basic idea. If you have more specific questions please post them here and I or someone else will be glad to help.

<b><font color=red>Fredi</font color=red> <font color=red>Fredi</font color=red> He's our man! If he can't do it no one can!</b>

 

[Crashman]

The memory you're looking at is Double Data Rate, the CPU bus is Quad Data Rate, so 133MHz=DDR266, but 133MHz=QDR533. Anyway, I'd suggest the Gigabyte GA-8SG667, or the revised versionof it, the GA-8SQ800, because they can run DDR400 with greater stability. Same chipset as the 648 Max.

<font color=blue>You're posting in a forum with class. It may be third class, but it's still class!</font color=blue>

 

[Flipphone]

i dont like any sis chipsets

 

[Crashman]

That's nice.

<font color=blue>You're posting in a forum with class. It may be third class, but it's still class!</font color=blue>

 

[Gregedit]

Thanks For the break down of it. I think I'm getting the Idea now.

Would i be correct in saying:
If the motherboard is capable of running 533/400 FSB, the motherboard would then "downstep" the signal from the processor to make it equal to the speed of the memory?

Is that correct or have i just confused myself again? Also... Based on your explination, I don't think that i fully understand what the definition of FSB really is.

You also mentioned:
"You want to run both the memory and the FSB at the fastest signals possible. The best configuration is for the FSB to be at the same effective speed of the memory bus."

So based on that, in your opinion, which option would you choose?

MSI 648 Max (SIS Chipset)

01. P4-2.53Ghz (400 FSB) with 512Mb DDR400
02. P4-2.80Ghz (533 FSB) With 512Mb DDR266

03. P4-2.53Ghz (400 FSB) with 512Mb DDR266
04. P4-2.80Ghz (533 FSB) With 512Mb DDR400

I think that I'll start looking at the Gigabyte motherboards because the MSI board can only Achive 512Mb with DDR 400. Are there any othe Tom's Shoot outs to do with the new motherboards?

Thanks for the help

 

[bum_jcrules]

Crash, that was just too funny. I love the sarcasim.


Gregedit,

Q1: Yes, in essence. Here is something that will visually show you how the signals are syncronized. It is a good sized PDF but if you have broadband it should be no big deal.

<A HREF="http://www.rambus.com/downloads/DRCG_d_0056_V1_3.pdf" target="_new">http://www.rambus.com/downloads/DRCG_d_0056_V1_3.pdf</A>

It is a layout of a DRCG, Direct Rambus Clock Generator. What I want you to look at is page 5. At the top of that page you will see the differences in clock signal speeds. The closer together the peaks and valleys the faster the signal is. (Higher frequency) The top signal is the system clock and the second is a generated signal speed to allow for the bottom signal. The bottom signal is the one that the FSB and the Memory bus will be syncronized at. (This is a RDRAM example but SDRAM applications are simillar.... this is just for illistrative purposes.)

I know that what I posted above was a little technical but if you read more you will get yourself up to speed.

Ultimately you want the memory bus and the FSB (Front Side Bus) to run at the same (effective) speeds. This way the the sycronizing clock is the same as both the system clock and the memory bus clock. (No bottleneck) See the table on page 5 to see the ratios.


Q2: FSB = Front Side Bus = the data pathway link between the Northbridge and the CPU. This like the coax cable between your VCR and yout TV.


In your options...

"04. P4-2.80Ghz (533 FSB) With 512Mb DDR400"

...would give you the best results. This where you would want Crashman to chime in again about specific motherboard and chipset performance.

<b><font color=red>Fredi</font color=red> <font color=red>Fredi</font color=red> He's our man! If he can't do it no one can!</b>

 

[Gregedit]

Thanks for the link.

I read it and understand how it works now.

I have decided to go for option 4 I have also taken Crash's advice and am going to get the Gigabyte GA-8SQ800 Ultra (Is this a good choice Crashman?). It supports Dual DDR which it pretty cool. I have read a basic explination about Dual DDR at overclockers.com that explained things for me. Later I found a post that asked the question:

Is it better, because of dual DDR, to use
1x 512 MB DDR400
or
2x 256 MB DDR400?

Unfortunately i never had time to complete reading the post and cant find it again so i was wondering if i could rattel your mind again with the question.

Once again... Thanks for the understanding
Cheers

 

[bum_jcrules]

2 x 256MB for better bandwidth.

Here is a compatability chart from Giga-Byte.

<A HREF="http://tw.giga-byte.com/support/support_ddr400_8sq800u.htm" target="_new">http://tw.giga-byte.com/support/support_ddr400_8sq800u.htm</A>

<b><font color=red>Fredi</font color=red> <font color=red>Fredi</font color=red> He's our man! If he can't do it no one can!</b>

 

[Gregedit]

Thanks for the link.

I had a look at the compatability list and a question i have now is:

The board can only support 3 sticks of 512mb kingston or 4 sticks of 256mb of corsair.
Based on that, and if it is better to run dual sticks, is it possible to run
2x 512mb + 2x 256mb
or would i get better performance if i ran
4x 256mb.

Where im getting confused is if i can run 3 sticks if 512mb and lose 1 slot of if i can run 3 sticks of 512mb and fill the last slot with something else like 1x 256mb.

I have tried contacting the gigabyte support but they are still celebrating their new year till 5 Feb.

Thanks
I hope this will be the last dumb question i have for you. thanks for your patience.

 

[bum_jcrules]

The less sticks you use the better. Use two sticks of whatever, but use them in a even pair. (2 x 256MB or 2 x 512MB)

<b><font color=red>Fredi</font color=red> <font color=red>Fredi</font color=red> He's our man! If he can't do it no one can!</b>

 

[Gregedit]

Thanks alot for all you advice.
I'm gonna make my purchase next week.

Keep Well

 

[Flipphone]

had crappy compaq sis chipset never i again. i dont like sis chipsets crash lol

 

[bum_jcrules]

And that helped this discussion how?

<b><font color=red>Fredi</font color=red> <font color=red>Fredi</font color=red> He's our man! If he can't do it no one can!</b>