Hello I need an advice on External Clock Settings. 1 week ago I accessed my BIOS and changed external clock settings to 133 and my processor started working @ 1000MHz but before it worked @ 789MHz. Then i tried changing settings to something else and when i tried to turn on my computer to see the speed of my processor it did not start properly. There was something wrong. Some very big letters appeared on the screen and that was all. I removed BIOS battery to restore default BIOS settings, it worked but my windows XP did not start at all. I had to format my harddrive and install windows again. Can anyone explain how those external clock settings work? Thank you.

Knowing your MOBO might explain what happened to your system. The “External Clock Settings” control the clock speed of the memory bus on the motherboard. Once again, knowing “how those external clock settings work” on your MOBO depend on what MOBO you have. Settings are frequently found on the MOBO by jumper and as a choice on one of the BIOS pages.

The external clock settings are the speed of the Front Side Bus, the thing that moves data between the CPU and the rest of the system. Adding (or subracting) to that setting increases the speed that the FSB runs at. This sounds great because now the CPU can communicate faster. But it also raises the CPU internal frequency, the speed of the chip that everyone talks about. This makes it faster, but also heats it up. Also, changing the front side bus can also change the speed of the PCI bus, which should be kept as close to 33 mhz as possible. By choosing some random setting, you could have changed the speed of the PCI bus too far out of spec and corrupted the hard drive, explaining the need for a reinstall. A good idea is to keep the PCI bus below 37 or 38 Mhz and you should be fine. I've seen computers with high quality components be perfectly stable at 42.5 Mhz, though. Anyway, to determin the speed of the PCI bus, there is a divider that takes the FSB and divides by, oh say, 3 or 4 or something. At 100 Mhz it divides by 3, at 133 Mhz, it divides by 4, either way, it is almost exactly 33 Mhz PCI bus, at random setting, it divedes by whatever its at, which could end up like 66 Mhz if not careful, and would corrupt HDD.