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How Operating Systems Work
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  › Introduction to How Operating Systems Work
› The Bare Bones
› Wake-Up Call
› Processor Management
› Memory and Storage Management
› Device Management
› Interfacing to the World
› Once and Future Differences
› Lots More Information!

Wake-Up Call
When the power to a computer is turned on, the first program that runs is usually a set of instructions kept in the computer's Read-Only Memory (ROM) that examines the system hardware to make sure everything is functioning properly. This Power-On Self Test (POST) checks the CPU, memory, and basic input-output systems for errors and stores the result in a special memory location. Once the POST has successfully completed, the software loaded in ROM (sometimes called 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.

The bootstrap loader is a small program that has a single function: It loads the operating system into memory and allows it to begin operation. In the most basic form, the bootstrap loader sets up the small driver programs that interface with and control the various hardware sub-systems of the computer. It sets up the divisions of memory that hold the operating system, user information and applications. It establishes the data structures that will hold the myriad signals, flags and semaphores that are used to communicate within and between the sub-systems and applications of the computer. Finally it turns control of the computer over to the operating system.

The operating system's tasks, in the most general sense, fall into six categories:

  • Processor management
  • Memory management
  • Device management
  • Storage management
  • Application Interface
  • User Interface
While there are some who argue that an operating system should do more than these six tasks, and some operating system vendors that build many more utility programs and auxiliary functions into their operating systems, these six tasks define the core of essentially all operating systems. Let's look at the tools the operating system uses to perform each of these functions.

 
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Table of Contents:
› Introduction to How Operating Systems Work
› The Bare Bones
› Wake-Up Call
› Processor Management
› Memory and Storage Management
› Device Management
› Interfacing to the World
› Once and Future Differences
› Lots More Information!

 
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