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View Full Version : 133MHz FSB jumper, what is for?



andreadebiase
02-28-2001, 09:08 AM
hi, technical question:
my mobo (FIC AZ11E) has a jumper for 100MHz or 133MHz FSB and the manual doesn`t say anything more. I would like to know if this is the jumper that is supposed to be set accordingly to the kind of SDRAM used (100 or 133 SDRAM).
Thanks

blazer2boy
02-28-2001, 09:51 AM
I believe that it is the Processor that it relates to.

If your processor requires an FSB of 133mhz than you would need to
have the jumper set to 133mhz setting. If running a processor with a 100mhz FSb than you would set the jumpers to 100mhz

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hiredgoonz
02-28-2001, 04:17 PM
The fsb speed should correspond to the type of processor you have...if it's a P2 350-450...it would be 100, if it's a P3 it could be either 100 or 133, while all but the newest celerons run at 66)...but if it's supposed to be 133 and you have the fsb jumper set to 100, then you are underclocking your processor...

Processor clock speed = multiplier x fsb...starting with the P2, Intel locked the multiplier on their cpus, which prevented one way of overclocking them...the fsb on some boards is adjustable so overclocking of pentiums did not die altogether...

What you need to figure out is what fsb speed your cpu is supposed to run at and make sure the jumper is set correctly...

bunk
02-28-2001, 04:19 PM
The FSB setting affects both the cpu and the speed of the RAM. It basically is the speed at which RAM runs at and a fraction of the speed at which the cpu runs at. You need to match both the CPU and the RAM to the speed of the front side bus.

The RAM is straight forward, if you set fsb to 133 you need to use pc 133 RAM. The CPU speed is set to run at a multiple of the fsb speed. This makes it important to match the CPU to the fsb. For example an 800mhz CPU that is meant to run on a 100 mhz bus uses a multiplier of 8x (8 x 100 = 800). A 800 mhz CPU that is meant to run on a 133 fsb would use a multiplier of 6x (133.333 x 6 = 800). Trying to run an 800 mhz CPU designed for a 100 mhz bus on a 133 fsb could cause problems as it would try to run at a multiplier of 8x on a 133mhz bus or 1066 mhz.

The two most noticeable examples of CPUs which can be bought at either fsb speed are the 600 mhz and the 800 mhz. With these they should have a listing of which fsb speed they were made to run.

That said if you are buying parts you should buy for the 133 mhz fsb. The faster the fsb the more data that can be sent to the CPU in a given amount of time. The multiplier is simply how much faster the CPU runs compared to the fsb. When the CPU is set too fast compared to the fsb the CPU will have idle time as it completes it work on the current data and is still waiting for the RAM to send the next batch. The cutoff point on CPU effeciency is somewhere between 4.5x and 6x. This is why the 800 mhz CPU running 6x on a 133fsb is faster than an 800 mhz CPU running 8x on a 100 fsb. The 133 fsb is send 1/3 more data to the cpu in a given amount of time thus giving the CPU more to work with. The 8x100 system is outracing the RAM and then when it does get data it is getting less than the 6x133.

Adrenaline
03-02-2001, 04:07 PM
This is for Bunk... ummm... no. Although you have some good technical specs here, your first sentence is wrong.

FSB MHz speed can refer to either the CPU, or the memory. They are NOT always the same. A system can have a CPU FSB speed of 133, and the memory at 100. It is possible.

As far as this exact board, I am unsure as I have not used it. Checking with the MFG is the best approach.

... never summer.