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FSB and memory confusing me!!!

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krishcanag

krishcanag

Member
​
Joined
Jan 12, 2008
Hello

After much to and fro I think I will go with Abit IP35 Pro mobo, which has a max 1333MHz. On the abit web page

http://www2.abit.com.tw/test-report/ip35-pro.htm?2

It gives a list of supported memory. I want to choose a fast either a 1066 or 800MHz memory module 2X 1G.

e.g

1066 1GB OCZ OCZ2N1066SR2GK NA NA 5.5.5.15 DS Pass NA VDIMM=1.8v
FSB=800
DDR2-800 (1:2)

and

800 1GB OCZ OCZ2G800R22GK NA NA 4,5,5,15 DS Pass fail Vdimm=2.1v
CPU FSB=1333
DDR2-800 (5:6)

On the first one it says the memory is full 1066MHz but the FSB becomes 800
On the 2nd one the full speed of FSB is 1333 but that is with 800MHz memory.

So how does this work, can someone explain this whole issue, and given a choice which one of the 2 will produce a faster PC?

regards

krishan
 
Yes, it can be confusing. I'll try to keep it simple.

1) The basic speed of the computer's various components is controlled by the FSB (front side bus) and various multipliers of that speed. The speed is determined from a clock where the FSB speed is the inverse of the clock period.
2) The CPU's speed is = FSB*(cpu multiplier). Thus for a motherboard with a common default FSB=266Mhz that is using a CPU with a multiplier of 8, the CPU speed = 8*266Mhz = 2128Mhz ~ 2.13Ghz.
3) An Intel CPU is "quad pumped." That is a fancy way of saying that an Intel CPU moves data at a rate of 4*FSB, this is sometimes called the CPU FSB. So for example with a FSB of 266Mhz and the CPU FSB = 1064Mhz (often noted as 1066). Computers work in bits (zeros and ones) so rounding of numbers is present in my example but the actual data transferred does work out.
4) Memory speed is FSB*2*(memory multiplier).

So to summarize
1) given FSB in Mhz
2) CPU speed = FSB*(cpu multiplier)
3) CPU FSB = 4*FSB
4) memory speed = FSB*2*(memory multiplier)

Next lets take you're first example. There must be a typo where FSB=800 should be CPU FSB = 800. Anyway, the memory multiplier is 1:2 (or divide by 1 and multiple by 2) so that from the formula
memory speed = 800Mhz = FSB*2*2 and I find the FSB must be
FSB=800Mhz/(2*2)=200Mhz
and the Intel CPU FSB = 4*FSB = 800Mhz
so the example is consistent.

The second example assumes a FSB of 333Mhz. I determine that from the memory speed formula again where
FSB = 800/(2*6/5) = 333Mhz
and the CPU FSB = 4*333 = 1333Mhz.

Realize of course that all I've done is tell you how the numbers you quote were determined. It doesn't tell you which memory to buy.

The quick answer to that question (my recommendation) is if you're not going to overclock then buy the 800 memory, if you're going to overclock then buy the 1066.

Apologies for the long answer.
 
deeppow said:
Yes, it can be confusing. I'll try to keep it simple.

1) The basic speed of the computer's various components is controlled by the FSB (front side bus) and various multipliers of that speed. The speed is determined from a clock where the FSB speed is the inverse of the clock period.
2) The CPU's speed is = FSB*(cpu multiplier). Thus for a motherboard with a common default FSB=266Mhz that is using a CPU with a multiplier of 8, the CPU speed = 8*266Mhz = 2128Mhz ~ 2.13Ghz.
3) An Intel CPU is "quad pumped." That is a fancy way of saying that an Intel CPU moves data at a rate of 4*FSB, this is sometimes called the CPU FSB. So for example with a FSB of 266Mhz and the CPU FSB = 1064Mhz (often noted as 1066). Computers work in bits (zeros and ones) so rounding of numbers is present in my example but the actual data transferred does work out.
4) Memory speed is FSB*2*(memory multiplier).

So to summarize
1) given FSB in Mhz
2) CPU speed = FSB*(cpu multiplier)
3) CPU FSB = 4*FSB
4) memory speed = FSB*2*(memory multiplier)

Next lets take you're first example. There must be a typo where FSB=800 should be CPU FSB = 800. Anyway, the memory multiplier is 1:2 (or divide by 1 and multiple by 2) so that from the formula
memory speed = 800Mhz = FSB*2*2 and I find the FSB must be
FSB=800Mhz/(2*2)=200Mhz
and the Intel CPU FSB = 4*FSB = 800Mhz
so the example is consistent.

The second example assumes a FSB of 333Mhz. I determine that from the memory speed formula again where
FSB = 800/(2*6/5) = 333Mhz
and the CPU FSB = 4*333 = 1333Mhz.

Realize of course that all I've done is tell you how the numbers you quote were determined. It doesn't tell you which memory to buy.

The quick answer to that question (my recommendation) is if you're not going to overclock then buy the 800 memory, if you're going to overclock then buy the 1066.

Apologies for the long answer.
Click to expand...

Thanx Deepow. I always wanted to kno that too. Dont worry about the answer, more is better :)
 
Deeppow

Fantastic post, I now understand this issue and I take it that both should be equal.

My present PC.

CPU CLK speed 2.13G
MUltiplier 8
FSB 266
CPU FSB 1066 (CPU-Z)

MEMORY is 667M PC-5300

working out from your exmaple

CPU FSB already as stated 1066
memory speed = 266 * 2 * 2 = 1066, where there must be like exmaple one a ratio of 1:2 hence like before 2* 2, Do you agree?

regards

krishan

PS. How and what sets the ratio (1:2 or 5:6) is it a automatic process after plugging in memory?
 
i think you might be off on that... since the fsb selected for the cpu is 266x4=1066. looking at the ram speed its 266x2=533.

if your using the IP35-PRO and tring to figure out what ram ratio to use. they are set like this here www.ocforums.com/showpost.php?p=5090361&postcount=2
for the 1:2 ratios that would simply take 2xfsb speed.

after installing the ram you would have to set the ram ratio...
 
Last edited:
Evilsizer said:
i think you might be off on that... since the fsb selected for the cpu is 266x4=1066. looking at the ram speed its 266x2=533.

if your using the IP35-PRO and tring to figure out what ram ratio to use. they are set like this here http/www.ocforums.com/showpost.php?p=5090361&postcount=2
for the 1:2 ratios that would simply take 2xfsb speed.

after installing the ram you would have to set the ram ratio...
Click to expand...

I thought looking at the example by deeprow both sides must be equal,ie.

3) CPU FSB = 4*FSB
4) memory speed = FSB*2*(memory multiplier)

therefore
1066 = 4 * 266, ok
667 = 266*2*(memory multiplier)
667 = 266*2*5/4

So yes I was wrong, looks like memory multiplier is 5/4

krishan
 
Last edited:
i think he did a typo... since the ram speed is just FSBxA, where A equals the ram ratio selected. i even reread it about the memory and that left me confused... when lookint at the ddr2-xxx rating its gonna be 2 times the speed you find from FSBxA. like if you had a fsb of 266 with a ram ratio of 1:2. 266x2=533mhz, then for it would be DDR2-1066. after thinking about it, seems his equation was giving you the DDR2 speed. to me then it would be like FSB x A= single data speed x B = DDR2(where B is by 2 for DDR,double data rate),giveing you the ddr2 speed. i now think thats what he meant...
 
Evilsizer said:
i think he did a typo... since the ram speed is just FSBxA, where A equals the ram ratio selected. i even reread it about the memory and that left me confused... when lookint at the ddr2-xxx rating its gonna be 2 times the speed you find from FSBxA. like if you had a fsb of 266 with a ram ratio of 1:2. 266x2=533mhz, then for it would be DDR2-1066. after thinking about it, seems his equation was giving you the DDR2 speed. to me then it would be like FSB x A= single data speed x B = DDR2(where B is by 2 for DDR,double data rate),giveing you the ddr2 speed. i now think thats what he meant...
Click to expand...

If I get what you are saying it is this, he wrote

memory speed = FSB*2*(memory multiplier)
but if memory speed is already given in DDR2, then
my 667 DDR2 = FSB*(memory multiplier)
therefore
667 = 266*5/2

Therefore the ratio is 5/2, now suppose I did have this kit and powered up first time, are u saying I need to go striaght into BIOS to set memory ratio?

krishan
 
you were right with the 5:4 ratios i havent seen the ip35-pro give 5:2 ratio when looking at cpuz. thats the only time i see something other then what the ss i took of the bios is.. since the bios is 1:1.x or 1:2 it assumes that 1 is the fsb where the other side is the multiplier for ram speed. thats what i was going on, i should have been more clear,sometimes im not, sorry. from the bios stand point if your fsb is 266mhz and your ram is saying ddr2-667, then the ratio you have selected is the 1:1.25 in bios. that may be 5:4, i havent kept up with the ratio's reported by cpuz. its easier for me to just go by the ratio in the bios to figure out the ram speed.

to answer though no the bios does not auto set to the rams rated speed. often times the boards boot with a safe speed like ddr2-667. then you have to change it to its rated speed.

i should have asked though what ram did you wind up getting?
 
Evilsizer said:
you were right with the 5:4 ratios i havent seen the ip35-pro give 5:2 ratio when looking at cpuz. thats the only time i see something other then what the ss i took of the bios is.. since the bios is 1:1.x or 1:2 it assumes that 1 is the fsb where the other side is the multiplier for ram speed. thats what i was going on, i should have been more clear,sometimes im not, sorry. from the bios stand point if your fsb is 266mhz and your ram is saying ddr2-667, then the ratio you have selected is the 1:1.25 in bios. that may be 5:4, i havent kept up with the ratio's reported by cpuz. its easier for me to just go by the ratio in the bios to figure out the ram speed.

to answer though no the bios does not auto set to the rams rated speed. often times the boards boot with a safe speed like ddr2-667. then you have to change it to its rated speed.

i should have asked though what ram did you wind up getting?
Click to expand...

ok I understand, so maybe my first caluationis correct then.

Now I have not bought anything yet, I have never built anything and am just getting into all this PC stuff in the last few weeks. Its winter!!!
I think I will go with a gigabyte GA-P35-DS3R or L, I was a fan of getting the abit ip35 pro, but find that abit flashmenu only works with the later BIOS versions not the first, if I order such a board and get the first BISO I have to use the floppy disk procedure which I find I am not too sure how to do it. Gigabyte, you can use USB.

regards
krishan
 
well the new boards have no issues with flashmenu. thats not to say you wont though as a windows based bios flash util is never a recommended way to go. with abit and many other now you are in luck.. put bios on cd, hit ALT-F2 on bootup of the system and it loads the bios from the cd to flash with. i have one of the first boards for the IP35-Pro and never had any issues with flashmenu. since your buying now your getting a later rev board then mine. since they made some minor updates that helps with ocing or something else... really dosent seem that much different then mine...
 
krishcanag, my apologizes for being late. I've been out of town and am in fact still away from home. I'm very glad Evilsizer did provide help but let me clarify a little more.


Evilsizer said:
i think he did a typo....
Click to expand...

Actually I didn't have a typo. What I wrote is how the memory speed works. As Evilsizer noted the 2 in my equation,
memory speed = FSB*2*(memory multiplier),
relates to the double in DDR (Double Data Rate) memory.

However, how a particular motherboard manufacturer may present this information to you in its BIOS may be a different matter. And as Evilsizer once again noted, they may present it to you as
memory speed = FSB*A
where in this case A=2*(memory multiplier).
I would say that this is indeed a simplier way to present you the info and doesn't require you to know the info I told you.

They can also let you just tell them the memory speed itself. If the chipset is a Nvidia chipset the options available to you are very broad and you can even underclock the memory. If you chipset is Intel your choices are much more limited and you can't underclock with most chipsets. Whatever the options, the BIOS will then select a memory multiplier and you don't have to do the arithmetic and select a multiplier.

For example, my ASUS' gives me options for the final memory speed and the manual discusses these in terms of speeds that represent 6 different multipliers. These are 667, 800, 835, 1002, 1066, 1333. Considering a default FSB of 266, you can easily determine the memory multiplier.

I'm not sure what the Abit IP35-Pro does, nor can I tell from their manual. But I'm pretty sure when you're in the BIOS themselves it will be easy to see what the multipliers are.

Whatever the case, the basics are the same. :beer:
 
yea Deep i noted later you were right.. i was going it might have been wrong with the approch i was using...

the IP35-pro and gigabyte boards are pretty close in reguards to selecting the memory ratio. the gigabytes are just multis like a cpu 2x= 1:1 and so on... abit gives it to in 1:1/1:1.25 as you can see from post#5 where i have bios ss's up. they assume the 1 is the fsb by the multi which is then 1/1.20/1.25...
 
thanks guys

very good to have guys who know the issue and take time to respond like this. I feel quite confident when I get my mobo and stuff that I know what I am doing.
thanks again

krishan
 
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