In explaining what a computer does when it boots we must first define what it means to boot.com, to boot a computer is to load an operating system into the computer's main memory or random access memory. Once the operating system is loaded and you see the initial window the computer is ready for users to run applications. The following is what happens in that boot process to get a user to the point of running applications:.
1. Power-On Self Test (POST) .
When the power is turned on the computer the ROM BIOS begins the boot process by giving commands. Stored in Read Only Memory (ROM), on the BIOS chip, is a small set of software instructions that allow the computer to begin the process of self testing and configuration. These instructions include a series of diagnostics or power-on tests including:.
Video Test: initializes the display adapter, tests the video card and video memory, and displays configuration information or any errors. Of course you won't be able to see these errors if your display is malfunctioning. BIOS Identification: displays the BIOS version, date, and manufacturer. Memory Test: tests the memory chips. A running sum of the amount of memory tested will display up to the total amount of memory installed. An error message here indicates a faulty memory chip that will require replacement.
2. System Initialization, CMOS and BIOS Check .
After a successful POST the instructions stored in the BIOS will initialize the system from settings stored in CMOS. The CMOS is where information such as date and time, hard disk settings, etc. is stored .
After reading in the CMOS settings the boot sequence will continue with:.
PCI Initialization - If you have a PCI bus the system will now initialize the cards on the bus.
Configuration Display - The BIOS now tests and displays the system configuration, including the status of:.
CPU.
Floppy drives.
Mouse and keyboard ports.
Serial ports.
Parallel ports.
Cache memory information.