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Chapter 2. Hardware Basics > What an Operating System Does

What an Operating System Does

When you first turn on your computer, you hear the fan spinning and the disk drives start churning. The first program to run is the computer's ROM (read-only memory). This is a lot like waking up in the morning; you blink and make sure that you still have two hands, two arms, two legs, and everything is ready to go. The boot program checks the system hardware to make sure it's all connected and ready to go. The POST (power on self-test) looks for errors in the CPU, memory, and the BIOS (basic input-output systems). Once the POST is complete, the ROM will activate the drive where the boot information is stored. The OS's bootstrap loader is activated.

The bootstrap loader is a program with one function: to load the OS into active memory. Once the OS is loaded, it begins to administer the various categories of jobs it must do. These include processor, device, storage memory management, and user and application interfaces, among other mundane details. If the OS encounters an error at any point, it cannot continue. These are called boot failures.


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