The old BIOS supported processor speeds up to only 450MHz. Now, processors are capable of running 1GHz. You must upgrade the system BIOS to support higher operating speeds for the processor. With many Slot 1 system boards, you will not have any problems upgrading to 1GHz, provided that you get the newest BIOS version; however, this is not true for every system board. You should have checked the chipset and BIOS information before purchasing the new microprocessors. There is a chance that you will be able to upgrade only to 600MHz.