diffrence betweenpci lock@33mhz & EXTclk/4

could somenone plz explain the difference between these 2 settings in bios.i have my pci bus locked at 33 mhz.at ocworkbench review on the abit bd7II they set the pci at ext.clock4.i have the h\w strap set to low and divider at3\4.trying to work my way around this bios & i am thankful for the help i am getting here.thnx

pci lock at 33 locks your pci bus at 33Mhz and agp at 66Mhz
whatever you set the fsb to , this is very nice for overclocking as your pci and agp will be running at the correct speed.
Ext. Clock / 4 will set your pci bus to fsb / 4 eg 150 fsb gives 37.5 for pci and double that for agp 75
I would advise to use lock at 33.

Also set the mem timings manually not by spd as this board seems to change the settings when using spd.
some boots it would set 2,5,2,2 and others it would set the correct 2.5,6,3,3

HTH