CMOS hold the settings for each device such as what to boot off of first . Where as the BIOS are the basic programs that start every basic peace of hardware in the pc such as keyboard, hard drive, ect..the setup screen that you can access at boot is actually a CMOS setup utility and not actually a the BIOS as most people refer to them. however we all reffer to them as BIOS or CMOS eather one is fine.