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The Operating System (OS)
is the first thing loaded onto the computer—without the operating system, a computer is useless.
The purpose of an operating system is to organize and control hardware and software so that the device it lives in behaves
in a flexible but predictable way.
Not all computers have operating systems. For other devices, an operating system creates the ability to:
- serve a variety of purposes
- interact with users in more complicated ways
- keep up with needs that change over time.
All desktop computers have operating systems. The most common are the :
- Windows Family – developed by Microsoft
- Macintosh Operating Systems – developed by Apple
- UNIX Family of operating systems – developed by many, different individuals, corporations and collaborators.
POWER-ON SELF TEST(POST) – the first program that runs when the computer is turned on and a set of instructions kept
in the computer’s read-only memory(ROM). This code examines the system hardware to make sure everything is functioning
properly by checking the CPU, memory, and basic input-output systems (BIOS) for errors and stores the result in a special
memory location.
Once the POST has successfully completed, the software loaded in ROM(sometimes called the BIOS or firmware) will begin to
activate the computer’s disk drives. In most modern computers, when the computer activates the hard disk drive, it finds
the first piece of the operating system: the bootstrap loader.
Bootstrap loader – a small program that has a single function: It loads the operating system into memory and allows
it to begin operation.
* sets up the small driver programs that interface with and control the various hardware subsystems of the computer.
* Sets up the divisions of memory that hold the operating system, user information and applications.
* Establishes the data structures that will hold myriad (or multiple) signals, flags and semaphores that are used to communicate
within and between the subsystems and applications of the computer.
* Then it turns control of the computer over to the operating system.
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