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OPERATING SYSTEM: INTRODUCTION

The operating system can be thought of as the government of a computer. Unlike the hardware circuitry, which is inherently fixed, like governments, the operating system can be structured in a variety of ways. Each of the Windows families, the Macintosh family and Linux are operating systems that can run on essentially the same set of circuitry.

Operating systems were originally designed to run on large mainframes, where they had essentially the same function as they do on today’s personal computers and laptops. However, many of today’s handheld devices, such as personal digital assistants and cell phones, also have operating systems. In fact, the computer in a modern cell phone is more powerful than that of a 20-year-old desktop personal computer. It is possible for computers to run without an operating system, and the computers that control most household appliance are hard-wired, self-contained computers designed to perform one set of tasks very efficiently. While this is obviously attractive, it is inflexible, doesn’t permit the application of updates, patches, fixes, and therefore condemns a computing device to slow obsolescence. It is entirely possible and some sophisticated users choose to install two different operating systems on the same computer. In this case, the user can choose to “boot” into one or the other system at the time of booting up the computer. The operating system is the first thing that is loaded onto a computer in a process called bootstrapping, which will be described below, and without it, the computer cannot work.

BOOTSTRAPPING AND BIOS

Key Points

  • Power-on self-test (POST) for hardware components in the system to make sure everything is working properly.

  • Activating other basic input-output system (BIOS) chips on cards installed in the computer, i.e., SCSI and graphics cards.

  • Provides low-level routines used by the operating system to interface to different input, output, and other hardware devices, i.e., the keyboard, the screen, and the serial and parallel ports.

  • Manage settings for the hard disks, clock, and so on.

Computer Power On

The first thing that happens when a computer is turned on is an activity wherein a set of instructions called the BIOS are run from the computer’s read-only memory (ROM). The BIOS loads interrupt handlers and device drivers and it initializes the computer’s registers and power management. Interrupt handlers are small programs acting as translators between hardware components, like the mouse and keyboard, and the operating system. When the user presses a key on the keyboard, the value or name of that key is stored in a buffer (temporary storage area) and the keyboard sends an interrupt to the operating system indicating that there is something in the buffer. The operating system can decide what to do about the interrupt and when. Some keyboard combinations (like Ctrl, Alt, Delete pressed together) may generate interrupts that have a higher priority ...

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