Operating Systems - part 01

Define Operating System

•          A program that controls the execution of application programs

•          An interface between applications and hardware

 An Operating System is a computer program that manages the resources of a computer. It accepts keyboard or mouse inputs from users and displays the results of the actions and allows the user to run applications, or communicate with other computers via networked connections.

Layers of a Computer System

Main Responsibilities of OS

·         Perform basic tasks, such as recognizing input from the keyboard, sending output to the display screen, keeping track of files and directories on the disk, and controlling peripheral devices such as disk drives and printers.

·         Ensure that different programs and users running at the same time do not interfere with each other.

·         Provide a software platform on top of which other programs (i.e., application software) can run.

Services typically provided by an OS

·         Program Creation (editor, compiler)

·         Program Execution

·         Access to I/O devices

·         Controlled access to files

·         System Access (logging in)

·         Error detection/response

·         Accounting

Booting of computer

·         Booting (also known as "booting up") is a bootstrapping process that starts operating systems when the user turns on a computer system.

·         A boot sequence is the initial set of operations that the computer performs when power is switched on.

·         The bootloader typically loads the main operating system for the computer.

·         Power-on self-test (POST) is pre-boot sequence.

·         It is the first step of booting, or bootstrapping.

The principal duties of the main BIOS during POST :

·         Verify the integrity of the BIOS code itself

·         Find, size, and verify system main memory

·         Discover, initialize, and catalog all system buses and devices

·         Pass control to other specialized BIOSes (if and when required)

·         Provide a user interface for system's configuration

·         Identify, organize, and select which devices are available for booting

·         Construct whatever system environment that is required by the target OS.