Computer Software

Two Major Types of SW System SW Programs that generally perform the background tasks in a computer. These programs, many times, talk directly to the HW Application SW Programs that generally interact with the user to perform work that is useful to the user. These programs generally talk to the HW through the assistance of system SW

Types of SW

3 main types of SW licensees 1.Proprietary – Most software on a Windows PC or a Macintosh belongs to this category 2.Freeware – Most software on a Linux PC belongs to that category 3.Shareware – the category which lies between the above two categories

Proprietary SW License The user needs to pay the maker of the SW for buying a license that allows the user to use the SW The license, generally, does not transfer the ownership of the SW; it just allows the user to use it The user is legally barred from making copies of the licensed SW. Generally, the license is for the personal use only Most SW in use in the world is of this type Examples: Windows, Mac OS, MS Word, Adobe Photoshop, Norton Antivirus

Freeware SW License Also known as “Public Domain SW” Allows the user free use of the SW The author, however, generally retains ownership Can usually be downloaded from various Web sites Examples: Linux; LaTeX; Netscape Web browser – the Navigator; MS Web browser – the Internet Explorer

Freeware: Open-Source SW Some authors give away the machine code only, which is extremely difficult to modify, if at all! Others even give away the high-level language source code so that users can make changes according to their own requirements The later practice is called open-source licensing Examples: Linux; Netscape Navigator

Shareware SW License Allows the user free use of the SW, but with a request that the user pay the author a small amount (US$10-50) if the user is satisfied with the SW The author retains ownership Can usually be downloaded from various Web sites Examples: WinZip, Download Accelerator

Trialware Similar to shareware, but different The SW is usable for a short period only After an initial trial period that can range from a week to a few months, the SW self-destructs Can be downloaded from the Internet or alternatively, the user can receive a copy my snail-mail by writing to the maker of the SW Why trialware? So that the customer can have a risk-free trial for a limited-period only

Now to System Software…

Hardware Operating System Utility Language Translator Device Driver Scientific Apps. Business Apps. Productivity Apps. Entertainment Apps. System software Application software

System SW are programs that … Control the overall operation of the computer OS Interact directly with HW Device drivers Perform system management & maintenance Utilities Are used to develop or maintain other programs Language translators

The Booting Process Booting - the process of loading an operating system into a computer’s main memory

Kernel Command Interpreter (Shell) File Manager Device Manager GUI Loader OS Components

Kernel The heart of the OS Responsible for all the essential operations like managing resources, task scheduling, etc. Also contains low-level HW interfaces. Size important, as it is memory-resident

Core Tasks of an OS 1.Processor management 2.Memory management 3.Device management 4.File management 5.Application Interface 6.User Interface

Processor Management Various programs compete for the attention of the microprocessor. The OS plays the role of the honest referee, making sure that each application gets the necessary attention required for its proper execution. It tries to optimally manages the limited processing capacity of the microprocessor to the greatest good of all the users & apps

Memory Management Straight forward for a single-user, single tasking The OS ensures that: each application has enough private memory applications do not run into other application’s private memory. The OS is responsible for efficient utilization of hierarchical system memory (e.g. RAM, cache, etc.).

File Management A file system is a collection of directories, subdirectories, and files organized in a logical order The OS is responsible for maintaining the file system through indexing of filenames and their disk location. The OS can find any file in a logical and timely fashion

Device Management

Application Interface

User Interface Users communicate with the computer using a consistent user interface provided by the OS This UI can be a command-line interface in which a user types in the commands. Example: copy a:/file1.html c:/file1.html Or, it can be a graphical UI, where Windows, Icons, Menus, and a Pointing device (such as a mouse) is used to receive and display information. Example: With the help of the mouse, drag file1.html from drive a to drive c

Graphical User Interface

Command Line Interface

Types of Operating Systems Classification according to type of computers and applications they support 1.Real-Time Operating System (RTOS) 2.Single-User, Single Task 3.Single-User, Multi-Tasking 4.Multi-User, Multi-Tasking

RTOS (Real Time OS)

Single user/Single tasking OS OS designed to manage the computer so that one user can effectively do one thing at a time MS-DOS is an example single-tasking single- user OS with a command line interface Take up little space on disk Run on inexpensive computers

Single user/Multitasking OS Most popular OS, used by most of PCs and Laptops Lets a single user interact with several programs, simultaneously Mac OS, Linux Windows XP Require expensive computers Tend to be complex

Multi user/Multi tasking OS Many users connect to one computer Each user has a unique session UNIX, Linux, and VMS Maintenance can be easy Requires a powerful computer

Multi user/Multi tasking OS

OS Survey Summary

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