1. TexPREP Summer Camp Computer Science
Operating Systems
TexPREP Summer Camp
Computer Science

2. Software Software System software Application software
Operating Systems
System software
Utilities
Software
Application software
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.

3. 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
Linux
Mac OS
UNIX

4. Main tasks The main tasks of an OS are: Provide a user interface.
Provide an application software interface.
Coordinate activities among the computer resources.

5. 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.

6. 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.

7. Resources management Some of the resources that an OS must manage are:
Memory.
Processor.
Storage.
Peripheral devices.

8. 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.

9. 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.

10. 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.

11. 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.

12. The boot process
When 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.

13. 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.

14. 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 for example.
Text editors: allow the user to create/modify plain text.