Operating Systems

TexPREP Summer CampComputer Science

Software

Software

System software

Application software

Operating Systems

Utilities

System software: programs that manage the computer resources and provide an interface to application software and users. For example, operating systems, antivirus, compilers, etc.

Application software: programs that help the user to perform specific tasks. For example, word processors, spreadsheets, web browsers, etc.

Operating System (OS)

The OS is the most important program running on a computer because it controls all activities that take place within a computer system.

Some popular OS for personal computers are:• Windows Vista, 7, 8, etc.• Linux• Mac OS• UNIX

Main tasks

The main tasks of an OS are:

• Provide a user interface.• Provide an application software interface.• Coordinate activities among the computer

resources.

User interface

The user interface facilitates the interaction between the user and the computer system.

• Command-line: users must enter commands at a prompt.

• Menu-driven: users select commands from a menu.

• Graphical User Interface (GUI): users use windows, dialog boxes, menus, etc. to interact.

Application software interface

Application software access resources by making requests for services to the OS through application program interfaces (API).

If an application program needs a resource or service it requests it from the OS.

Typically, application software cannot access computer resources directly.

Resources management

Some of the resources that an OS must manage are:

• Memory.• Processor.• Storage.• Peripheral devices.

Resources management (cont.)

Memory:• Ensures efficient use of RAM• Implements virtual memory (VM)

Processor:Allocates the CPU for a small amount of time to

each program running on the system so each one of them can perform its task.

Resources management (cont.)Storage:Maintains the file system.Allocates space on storage devices.Manages access to files.

Peripheral devices:Handles input and output from and to

peripheral devices attached to the computer.This is typically done through device drivers.

OS Categories

One way to classify OS is:

• Single-user: only one person can access the computer at any moment.

• Multiple-user: many users can access the system at the same time.

• Network: many users can access the network.

OS Functions

OS can allow the system to perform multiple tasks simultaneously at different levels:

• Multitasking: several tasks can be executed simultaneously by a single CPU.

• Multithreading: several parts of a single task can be executed simultaneously by a single CPU.

• Multiprocessor: several tasks can be executed simultaneously by several CPUs.

The boot processWhen the computer is powered on the CPU accesses

the ROM to execute the BIOS that:• Runs the POST (Power On Self Test) to ensure all the

computer components are operational.• Executes the bootstrap loader. This is a program that

loads the OS from a storage device (hard disk drive, CD/DVD drive, flash drive, etc.) onto RAM. Once the OS has been loaded it is given the control of the computer.

Recovery (boot) disk: contains the basic system files that will start the computer when there is a problem with the installed OS.

Utility software

These are programs designed to help maintain the system. Some utility programs have been integrated into the OS.• File managers: allow the user to perform

operations on files or folders such as create, open, edit, view, print, rename, move, copy, delete, etc.

• Disk defragmenters: improve the system’s performance.

• Disk checkers: find and fix disks’ bad sectors.

Utility software (cont.)

• Backup: allow the user to save their files (pictures, videos, homework, etc.).

• Anti-virus: protects the system from malware (programs that can harm a computer system).

• Data compression: allows the user to put several files in a compressed folder so that it can be attached to an email for example.

• Text editors: allow the user to create/modify plain text.