How Booting Works Note: This procedure may differ slightly for Mac, UNIX, OS/2, or other operating systems. When you turn on your computer, chances are that the operating system has been set up to boot (load into RAM) automatically in this sequence: As soon as the computer is turned on, the basic input-output system ( BIOS ) on your system's read-only memory ( ROM ) chip is "woken up" and takes charge. BIOS is already loaded because it's built-in to the ROM chip and, unlike random access memory ( RAM ), ROM contents don't get erased when the computer is turned off. BIOS first does a power-on self test ( POST ) to make sure all the computer's components are operational. Then the BIOS's boot program looks for the special boot programs that will actually load the operating system onto the hard disk. First, it looks on drive A (unless you've set it up some other way or there is no diskette drive) at a specific place where operating system boot files are l...