Abit SL6 User Manual page 37

BIOS Setup 3-7
100MHz (1: 1: 1/3) each multiplied times 3 then (divided by 3)
or
100MHz (3/3: 3/3: 1/3) each multiplied times 3 then (divided by 3)
which both equal:
(divided by 3)
100MHz (3:3:1)
Now the final point about this table is that it does not show the necessary divider, i.e.
for the 100MHz (3:3:1) example you still need to divide each by 3, even though it
does not show that in the table.
Accordingly, for the 66MHz (2:3:1) you will divide each by 2 and for the 138MHz
(4:3:1) example you would divide each by 4. The first value in the parenthesis is the
value for the CPU's FSB, and because everything derives its working frequency
from the FSB, that value must always equal 1. So for (3:3:1) you need to divide by 3,
for (2:3:1) you need to divide by 2 and for (4:3:1) you need to divide by 4.
So for the 100MHz (3:3:1) example in the table above, to get the working values you
are taking the (3:3:1) numbers and multiplying by 3 then dividing by 3.
For another example, in the table you have 138MHz (4:3:1) (divided by 4). You can
look at it like this: 138MHz (1: 3/4: 1/4). Each multiplied times 4 will give you the
same value as 138MHz (4:3:1). (needing to be divided by 4 again). So that for the
FSB you have 4 divided by 4 giving you a value of 1, so that 138MHz will come out
to 138MHz.
CPU FSB value =138MHz x1=138MHz (approximate proper FSB value for this
CPU)
SDRAM value = FSB 138MHz x 3/4 = 103.5MHz (approximate proper value
for PC100 RAM)
PCI value = FSB 138MHz x 1/4 = 34.5MHz (approximate proper value for PCI
bus)
Giving you all the proper values (within a few MHz or so, its
never exactly precise)
Another way to look at it would be that for the 138MHz (4:3:1) example, you could
use this "maximum number" value of 4, and then you could divide FSB value of
138MHz by 4 which equals 34.5MHz. You could then use 34.5MHz as the base
number to be multiplied by the number for the components. So that:
User's Manual