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fsb and ram speed?

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tft

Member
Joined
Feb 22, 2002
Location
R.I.
whats the difference between fsb speed and ram speed? Does a higher speed ram mean you'll be able to get higher speed fsb?
 

deeppow

Senior Member
Joined
May 10, 2002
Location
Los Alamos, NM
For AMD systems,

whats the difference between fsb speed and ram speed?
At a fsb at or below 165, memory speed = fsb * 2 * 5/4.
At a fsb at or above 166, memory speed = fsb * 2.

Does a higher speed ram mean you'll be able to get higher speed fsb?
In general the answer is yes. Very cheap memory might make the statement not true.
 
OP
T

tft

Member
Joined
Feb 22, 2002
Location
R.I.
oh ok I see. I was under the impression that ram speed was just an independent factor. So the goal is a higer fsb speed with a lower divider? And if the ram says its rated at 400, does that mean your fsb will automatically run at 200?
 

deeppow

Senior Member
Joined
May 10, 2002
Location
Los Alamos, NM
oh ok I see. I was under the impression that ram speed was just an independent factor. So the goal is a higer fsb speed with a lower divider? And if the ram says its rated at 400, does that mean your fsb will automatically run at 200?

You might take a look at this link, I wrote it up a little while ago when I was trying to figure some of these things out. It tries to explain in more detail why and what you do.

So the goal is a higer fsb speed with a lower divider?
No but based on what I said you could draw that conclusion. The reason you would rather run at 166, instead of less, is that the memory is accessed synchronous at or above 166 instead of asynchronously below 166. Synchronous access yields better performance. There are some numbers quoted in the above link.

And if the ram says its rated at 400, does that mean your fsb will automatically run at 200?
No, most mobos will start out at either a fsb of 100 or 133 depending on jumpers or the bios. That is where you memory will start. The 200 rating (or DDR400) will only work at that level if you're able to set your fsb=200. Thus if you buy DDR400 memory and don't overclock it, you wasted your hard earned money. :cool:
 

james.miller

Member
Joined
Jun 8, 2002
Location
Dunstable, uk
deeppow said:
For AMD systems,


At a fsb at or below 165, memory speed = fsb * 2 * 5/4.
At a fsb at or above 166, memory speed = fsb * 2.

In general the answer is yes. Very cheap memory might make the statement not true.

for amd systems, memory speed= fsb * 2 period.
unless you have the memory set to +33 or +66. (asynchronous - which isnt worth the hassle) In which case, it would be
memory speed = fsb * 2 + 33 or,
memory speed = fsb * 2 + 66 respectivly

but the memory system doesnt run asnycronous unless you tell it to.
 

deeppow

Senior Member
Joined
May 10, 2002
Location
Los Alamos, NM
All this depends on the particular mobo in use. Thus both james.miller and I are right, or wrong, depending on how you want to look at that issue. I would say that we neither are clear enough. My statements are correct as relates to an Epox. :D
 

Fluxer

Member
Joined
Mar 2, 2002
Location
New York
For p4 systems with RDRAM --

The speed for RDRAM on a p4 with the i850 chipset is always: FSB * 8

(100 FSB = 100 * 8 = 800mhz RDRAM).

The only exception being if you set the RDRAM to "3x" in the bios which would then mean your memory speed is: FSB * 6

(100 FSB = 100 * 6 = 600mhz RDRAM).

The new intel chips with a 533 FSB(133mhz actual FSB, the FSB is quad pumped) support pc1066 rdram:

(133 FSB = 133 * 8 = 1064mhz RDRAM)
The RDRAM supporting an actual FSB 533 is marketed as 1066mhz though.