(G)MCH Strapping / Frequency Latch

[devoh]

Ok I confess.. I thought I understood this.. but I don't.

I have a E8500 which is a 1333 FSB chip on a GA-EP45-UD3P using Crucial Balistic PC 6400 cas 4 memory....

IN the BIOS is has this..

I set (G)MCH Frequency Latch to [Auto]

(G)MCH Strapping
x.xxA -> FSB 266Mhz
x.xxB -> FSB 333Mhz
x.xxC -> FSB 200Mhz
x.xxD -> FSB 400Mhz

The x.xx part seems to be connected to the memory speed via the FSB you set times x.xx

so 2.40B with a 400 FSB = 960 memory speed..
2.66C with a 400 FSB = 1064 memory speed..

I don't understand the letters after. 333Mhz x 4 = 1333 the speed of my chip's native FSB.. I have noticed that using a value 2.00X gives a 1:1 ratio.. well at least 2.00D does..

HELP PLEASE!!!!!!!!!!

-devoh

[Psycho101]

Re: (G)MCH Strapping / Frequency Latch

You've almost answered your own question.

The letters after the RAM dividers refer to which MCH Strap is currently in use. They corespond to the table you wrote:

(G)MCH Strapping
x.xxA -> FSB 266Mhz
x.xxB -> FSB 333Mhz
x.xxC -> FSB 200Mhz
x.xxD -> FSB 400Mhz

The differing Multiplier values are there because for example if you have DDR-1066 RAM, with a FSB of 333 you'd need a memory multiplier of 3.2 as 333 * 3.2 = ~1066

With a 400 FSB you would need a lower multiplier to reach the same RAM speed eg at 400 FSB the memory multi used to get 1066 would be 2.66 because 2.66 * 400 = ~1066.

a value of 2.00x for the memory multiplier is indeed the 1:1 ratio. This meaning that the RAM is being run at an actual clock speed of 400MHz (hence the 1:1 ratio with the FSB), but the RAM is Double Data Rate, it can transmit date twice per clock cycle, giving an effective 800MHz clock (hence the 2.00x designation).

[devoh]

Re: (G)MCH Strapping / Frequency Latch

You've almost answered your own question.

The letters after the RAM dividers refer to which MCH Strap is currently in use. They corespond to the table you wrote:

(G)MCH Strapping
x.xxA -> FSB 266Mhz
x.xxB -> FSB 333Mhz
x.xxC -> FSB 200Mhz
x.xxD -> FSB 400Mhz

The differing Multiplier values are there because for example if you have DDR-1066 RAM, with a FSB of 333 you'd need a memory multiplier of 3.2 as 333 * 3.2 = ~1066

With a 400 FSB you would need a lower multiplier to reach the same RAM speed eg at 400 FSB the memory multi used to get 1066 would be 2.66 because 2.66 * 400 = ~1066.

a value of 2.00x for the memory multiplier is indeed the 1:1 ratio. This meaning that the RAM is being run at an actual clock speed of 400MHz (hence the 1:1 ratio with the FSB), but the RAM is Double Data Rate, it can transmit date twice per clock cycle, giving an effective 800MHz clock (hence the 2.00x designation).

I am still not getting it.. Here is what I did

I used 2.66C with a 408 FSB and got 1088 for a memory speed..
I used 2.66D with a 408 FSB and got 1088 for a memory speed..

The C corresponds to FSB 200Mhz
The D corresponds to FSB 400Mhz

The way I read what you wrote they should not be the same. I even benched them and they gave the same results for latency and throughput of memory.

Let's say I have my FSB set to 400.. and I use 2.00x so my memory speed is 800Mhz.. I'm with ya to this point.
What does the A, B, C, or D at the end of 2.00x get me? I know they are different since it's easy for me to go 2.00D with a FSB of 500.. but I can't boot with a 2.00B and a 500FSB(maybe with a lot of extra tweaking).

Psycho101 you may neeed to wack me with a large stick.

- devoh

[kick]

Re: (G)MCH Strapping / Frequency Latch

heh yep..

If you dont set the latch to auto but instead use 333mhz the native 8500 cpu ref ,u will only have the B multipliers available for selection(for memory).

youre probably more used to the 5:4 etc.ratio type memory settings in bios.

If cpu ref frequency is entered manually and latch is set to auto you can manually put in a memory multiplier .so ref frequency(A) of 200mhz=800mhz fsb (200x4).
cpu say (A) x8=1600mhz

memory speed could then be be
(A)x 3.2 or 2.66 or 2.4 or 2.0 for ddr2 memory.etc




The only thing is where you say FSB 333mhz,its not actually that its a reference frequency for the fsb and the cpu and the memory.
At 333mhz,the fsb is 1333mhz(333x4).At 333mhz, the cpu speed is whatever multiplier you specify say 8x 333mhz.Memory speed is whatever multiplier you are using..etc.


the memory multiplier is the memory multiplier based on the reference speed forget about the corresponding frequency for a minute.



1.If you leave the reference frequency at auto it should allways give 333mhz for your cpu

2. if you leave the mch latch frequency at auto..you will then be able to use all of the memory multipliers..2.66 c will multiply 333 by exactly the same amount as 2.66 d .What will be different is secondary memory timings which wont be shown in bios.


When you get to around 500 fsb reference(2000 actual)+ or- 20 as youve already noticed.secondary timings come ito it more..check psychos sig and mine.

[Psycho101]

Re: (G)MCH Strapping / Frequency Latch

I used 2.66C with a 408 FSB and got 1088 for a memory speed..
I used 2.66D with a 408 FSB and got 1088 for a memory speed..

The C corresponds to FSB 200Mhz
The D corresponds to FSB 400Mhz

The way I read what you wrote they should not be the same.

The speed your memory will be set to will be the same if the multiplier values are the same.

2.66c is intended for configuring DDR-533 RAM to run at its rated speed on a 200MHz FSB, while 2.66D is for running DDR-1066 at its rated speed on a 400MHz FSB.

The letters refer to a specific set of latencies and timings not visible in the bBIOS that are applied to the northbridge and/or RAM. D is designed to be more compatable with a FSB of 400, while B is intended to do the same for 333 FSB.

To read further on the subject take a look here, where both 1:1 straps are compared at 399 FSB and 500 FSB.

For me the D strap alows me to run with a lower Static tRead value.

I'd be willing to bet if you set your tRead values on both channels one higher than the value used for 2.00D, you'll be able to boot with 2.00B. EG if you can boot at 2.00D with tRead = 9, and not boot 2.00B, change tRead to 10.

Not that I'd recomment using a higher tRead than you have to, it's just an example.

[devoh]

Re: (G)MCH Strapping / Frequency Latch

heh yep..

youre probably more used to the 5:4 etc.ratio type memory settings in bios.

If cpu ref frequency is entered manually and latch is set to auto you can manually put in a memory multiplier .so ref frequency(A) of 200mhz=800mhz fsb (200x4).
cpu say (A) x8=1600mhz

memory speed could then be be
(A)x 3.2 or 2.66 or 2.4 or 2.0 for ddr2 memory.etc



The only thing is where you say FSB 333mhz,its not actually that its a reference frequency for the fsb and the cpu and the memory.
At 333mhz,the fsb is 1333mhz(333x4).At 333mhz, the cpu speed is whatever multiplier you specify say 8x 333mhz.Memory speed is whatever multiplier you are using..etc.


the memory multiplier is the memory multiplier based on the reference speed forget about the corresponding frequency for a minute.


1.If you leave the reference frequency at auto it should allways give 333mhz for your cpu

2. if you leave the mch latch frequency at auto..you will then be able to use all of the memory multipliers..2.66 c will multiply 333 by exactly the same amount as 2.66 d .What will be different is secondary memory timings which wont be shown in bios.

My last CPU was a AMD Athlon XP1800+ on a KT266a motherboard... so this is all new to me..

How is it that using 2.66C or 2.66D gives the same performance? It's looks like 2.00B and 2.00D are also the same. But 2.00D you can up the FSB much higher than if you are using 2.00B. I am still missing something.

-devoh

[kick]

Re: (G)MCH Strapping / Frequency Latch

They arent....i personnally can get a higher fsb(2000) using a B multiplier but cant hold a better bandwidth using a D multiplier at fsb(2000).
At low fsb ref speeds(under 450) you can probably run all sorts of multipliers.
Check pyschos sig and mine+ must be lots of related *500 posts.

[Capt Proton]

Re: (G)MCH Strapping / Frequency Latch

The letters after the number represents the strap. A B strap is intended to be chosen when the default FSB is 333MHz. The D strap when the default FSB is 400MHz. Although the memory ends up running at the same speed, the rest of the system is running faster at 400MHz than 333MHz. Setting the B strap gives tighter auto timings to the memory and the MCH than the D strap. So, same memory speed, different timings, some you can see (memory timings) other you can't (MCH). The D strap will be easier to use to get the system stable at high FSB than the B strap.

[devoh]

Re: (G)MCH Strapping / Frequency Latch

The speed your memory will be set to will be the same if the multiplier values are the same.

2.66c is intended for configuring DDR-533 RAM to run at its rated speed on a 200MHz FSB, while 2.66D is for running DDR-1066 at its rated speed on a 400MHz FSB.

The letters refer to a specific set of latencies and timings not visible in the bBIOS that are applied to the northbridge and/or RAM. D is designed to be more compatable with a FSB of 400, while B is intended to do the same for 333 FSB.

To read further on the subject take a look here, where both 1:1 straps are compared at 399 FSB and 500 FSB.

For me the D strap alows me to run with a lower Static tRead value.

I'd be willing to bet if you set your tRead values on both channels one higher than the value used for 2.00D, you'll be able to boot with 2.00B. EG if you can boot at 2.00D with tRead = 9, and not boot 2.00B, change tRead to 10.

Not that I'd recomment using a higher tRead than you have to, it's just an example.

I maybe getting a dim light in the old light bulb....

Since I have PC-6400 ram... then I should be using the "D" values..

"A" (FSB 266) for people with DDR2-533
"B" (FSB 333) for people with DDR2-667
"C" (FSB 200) for people with DDR2-400
2.00"D" (FSB 400) for people with DDR2-800 or 2.66"D" for DDR2-1066??

[Psycho101]

Re: (G)MCH Strapping / Frequency Latch

Which strap you have to use depends on your current FSB. If you had it at stock 333 FSB, you'd be using 2.4B to get PC2-6400 speeds. At 400 FSB you could use either 2.00D or 2.00B and it would give the same PC2-6400 (DDR-800) speed, even though 2.00B is actually intended for running DDR-667 (pc2-5300) RAM at its rated speed.

Usually, if you're running a FSB 400MHz or more, use D. If you're running a stock 333 FSB, then use the most apropriate B multiplier for your RAM.

[devoh]

Re: (G)MCH Strapping / Frequency Latch

Which strap you have to use depends on your current FSB. If you had it at stock 333 FSB, you'd be using 2.4B to get PC2-6400 speeds. At 400 FSB you could use either 2.00D or 2.00B and it would give the same PC2-6400 (DDR-800) speed, even though 2.00B is actually intended for running DDR-667 (pc2-5300) RAM at its rated speed.

Usually, if you're running a FSB 400MHz or more, use D. If you're running a stock 333 FSB, then use the most apropriate B multiplier for your RAM.

I think I understand now. So what's the story on "C" is that like a legacy
FSB of 200?

Thanks all for the help!! so many different speeds
back in the day.. there was one bus speed... and we liked it!!

-devoh

[Psycho101]

Re: (G)MCH Strapping / Frequency Latch

The C straps would be used to get your RAM running at corect speeds witha 200 MHz FSB processor like an E5200 for example.

It's not always logical though. If I want to run a 400 FSB with 2.8GHz on the processor I have to set 2.66C to get my RAM at 1066. 2.66D simply does not work. Completely non-functional regardless of voltages and tRead values etc. YMMV

[kick]

Re: (G)MCH Strapping / Frequency Latch

Dont get too hung up on the letters.
Youve bought a board with a lot of adjustments,so you want to tune the system in bios.
Once you set the cpu reference frequency it determines 3 things:
the cpu speed (with possible adjustment by you)
the front side bus speed (no adjustment possible in bios)
the memory speed (with possible adjustment by you).

Taking air cooling as a given (most of us here) on intel 45 chipset and 775 socket.
Were using 470-510 cpu ref frequency (quads)
470-530 cpu ref frequency (duals).
Generally you want to get the cpu running as fast as possible(stable) ,with the highest fsb possible,depending on your memory.

The only memory multipliers that will be of much use to you are B and D 2:00 (2xcpu ref frequency)2:40(2.4x cpu ref frequency)and maybe 2:66(2.66x cpu reference frequency)

Lets say u leave your cpu reference frequency at 450mhz
use x8 on your cpu, and the 2.4 memory multiplier.
That should give you
3600mhz cpu speed
1800mhz fsb speed
1080mhz ddr2 memory speed
memory bandwidth around 7000Mb/s read?

Trying cpu reference frequency of 500mhz and drop cpu multiplier to x7 and using a 2:00 multiplier for memory.
3500mhz cpu speed
2000mhz fsb speed
1000mhz ddr2 memory speed
memory bandwidth around 8500Mb/s read?

Thats just a rough approximation example :no mention of voltages/timings etc:.Maybe your cpu would be happy at 8 x500 at 4000mhz.But even with a 7 multiplier and running at 100mhz less ,running your memory below its stated speed can provide more performance if the front side bus speed is higher.

[devoh]

Re: (G)MCH Strapping / Frequency Latch

Dont get too hung up on the letters.
Trying cpu reference frequency of 500mhz and drop cpu multiplier to x7 and using a 2:00 multiplier for memory.
3500mhz cpu speed
2000mhz fsb speed
1000mhz ddr2 memory speed
memory bandwidth around 8500Mb/s read?

Thats just a rough approximation example :no mention of voltages/timings etc:.Maybe your cpu would be happy at 8 x500 at 4000mhz.But even with a 7 multiplier and running at 100mhz less ,running your memory below its stated speed can provide more performance if the front side bus speed is higher.

Results with SiSoft Sandra 2009.SP2

I seem to be getting some real nice memory speeds from 2.00D and a 500FSB (well 502 at the moment) So my memory is running @ 1004Mhz
9.28GB/s with a 68ns random access.

If I use 2.66D with a 408Mhz FSB(to keep the core @ 3.5Ghz for both tests). So my memory is running @ 1086Mhz. I only get 8.37GB/s with 78ns ramdom access.

So even though in the second example I have a faster memory speed, I get a much faster memory access and transfer speeds using a slower memory speed with a higher FSB and a 1:1 ratio.. fasinating! Faster memory does not necessarly make for faster random acess and transfer speeds. Not what you would expect.. well not me at least.

Just like you said it would be.

-devoh

[devoh]

Re: (G)MCH Strapping / Frequency Latch

Well I have gotten to 515FSB with a 2.00D and a 9 tRD. I can go higher
but not without losing my 9 tRD and some larger bumps to the MCH... so I'm pretty much at the point of diminishing returns. My goal is 4 to 4.2Ghz so with being able to use multipliers up to 9.5 I'm all set to start pushing the CPU.

-Devoh