Athlon 900 MHz Front Side Bus

LAST EDITED ON Mar-27-01 AT 06:36 PM (GMT)
"Rule of thumb; if last letter of an AMD CPU part number is B=200 FSB or C=266 FSB
There is a BIG difference in these devices, as the BUS_FREQUENCY_MULTIPLIER
is hard-wired on the device..."
"At any rate, using the A1200AMS3C device with a 200 MHz FSB will give a CPU
speed of 900 MHz.
(1200/266*200 = 902) the BIOS will actually report the 900 MHz speed in this
case, even though a 1.2GHZ processor is in the socket!!!
Similarly, all other Athlons, which are available in both 200 and 266 FSB's
have this same characteristic.

Example, the OPNs for the 1.2G Athlon are:
A1200AMS3B for an Athlon1.2G with 200 MHz FSB
A1200AMS3C for an Athlon1.2G with 266 MHz FSB"
See http://www.amd.com/products/cpg/athlon/techdocs/pdf/23792.pdf for more info.
Larry

1. RE: Athlon 900 MHz Front Side Bus
gjhoos May-06-01 05:48 PM
In response to message 0

Hi Larry,
I am getting this problem too on my KT7A with a 1.2 / 266 FSB CPU as showing up as a 900Mhz at boot up. Is what you are saying is that my PC will only run as a 900, or is the 900 just a false reading and the PC is actually running at a 1.2? Or will it run as a 900 until I manually set the processor speed in the Bios? Using softwmenu III, it shows I can set it at a max of 1250 mhz. Any info you can provide would be greatly appreciated, for this is my first time building an Athlon box. Thanks!

George

2. RE: Athlon 900 MHz Front Side Bus
lbyard May-06-01 08:38 PM
In response to message 1

If you run a 266 FSB processor with a 200 MHz FSB (2*100), you get (1200*200/266 = 902 Mhz for the CPU speed, which is the real speed). I have not got a KT7A on hand to check, but changing the CPU FSB Plus to 33 MHz in the Softmenu III in the CMO Setup should fix the problem. The CPU FSB/PCI Clock should remain at 100/33 Mhz. The FSB then becomes 100+33 MHz =133 MHz (or 2*133 =266 between the Northbridge and the processor) if I understand the user manual (and everything) correctly (I might not have it right). Then divide the correct CPU speed by 133 to determine the correct multiplier setting = 1200/133 = 9. I’ll dig deeper tomorrow if it doesn’t work. In any event, let us know if it does work, OK? Larry

3. RE: Athlon 900 MHz Front Side Bus
lbyard May-10-01 06:48 PM
In response to message 2

Got this via E-Mail
Hi Larry,
I tried your solution for "Athlon 900 MHz Front Side Bus" and it
worked like a charm. Thanks for the advice!
George