COM111 Lecture Schedule 4

COM111 Lecture Schedule 4

Introduction to Software, Categories of Software, System Software, Evolution of Operating System, Types of Operating System, Functions of Operating System.

Introduction to Software

The set of instructions which control the sequence of operations are known as programs and collectively programs are called software. It is responsible of controlling, integrating and managing the hardware components of the computer to accomplish specific tasks. A set of programs, which are specifically written to provide the user a precise functionality like solving a specific problem is termed as software package.

Categories of Software

 Software can be categorized as System software and Application software

1.      System software: It consists of several programs, which are directly responsible for controlling, integrating and managing the individual hardware components of computer system. It is the generic term for referring to any computer program whose purpose is to help the user to run the computer system. It acts an interface between the hardware of the computer and the software applications. Some examples of system software are operating systems, device drivers, language translators and system utilities. 

2.      Application software: Application software is dependent on system software and performs specific tasks. They include a larger collection of related but independent programs and packages, which have a common user interface or shared data format. Examples include Microsoft Office suite, Adobe Reader etc.

Examples of System software

Operating system (OS): It acts as an interface between the user and computer system. The operating system is the most important program that runs on a computer. Every general-purpose computer must have an operating system to run other programs and applications. Operating systems 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. The two main objectives of OS include managing hardware and providing an interface. Examples: Windows, Linux, Unix and Mac OS, etc.,

Device drivers: They are system programs, responsible for proper functioning of devices. Every device has a driver program associated with it for its proper functioning. Whenever a new device is added to the computer system, a new device driver must be installed before the device is used. A driver acts like a translator between the device and program.

Language translators: computers only understand machine language (0’s and 1’s) and it is difficult for a programmer to understand the machine language. Thus high level programming languages were developed to ease the burden of a programmer. Language translators are tools which converts programming languages into machine language. They are divided into three major categories: compiler, interpreter and assembler.

System utility: they are programs which perform day-to-day tasks related to the maintenance of the computer system. They are used to support, enhance and secure existing programs and data in the computer system. Most common functions of system utilities include file management, backup, data recovery, virus protection, disk management, firewalls and disk cleanup.

Evolution of Operating System

The evolution of operating systems went through major phases. Earlier days computer lacked any form of OS. Initial OS were of libraries of support code which linked to the users program to assist in operations like input & output which were hardware dependent. In 1960 IBM developed S/360 OS series of machines. After the microprocessors existence standardized OS like CP/M-80 for 8080/8085/z-80 microprocessors was developed. With development in microprocessors like 386,486 and Pentium series by intel computing world took new dimension, AT & T and Microsoft came with character based OS like Unix and DOS respectively. Microsoft and Apple Macintosh came with Windows 3.1, XP, Red Hat Linux, MAC …… , GUI- based OSs suited for personal computers.

Types of operating system

Operating System	Features	Application
Batch Processing	Ø  One program run at a time Ø  Large no. of repetitive jobs Ø  First-in, first-out scheduling	Payrolls & Mainframe computers
Multi-user / Timesharing	Simultaneous user interaction, On-line file systems	Computer networks
Multi- Programming/ Multi-tasking	Processor multiplexing, processor switch between process	Windows
Real-time(RTOS)	Ø  Respond to an event within a predefined time Ø  Respond quickly	Telecommunication, flight & railway reservation, military
Multi-processor	Ø  Parallel processing concepts Ø  Increase system throughput by doing work in less time	Super computers for scientific purpose
Embedded	Ø  Self contained in the device & resident in ROM Ø  Offer real-time OS qualities	Household appliances, car management systems, traffic control systems, energy management systems

Functions of an operating system

The main functions of operating systems

1.      Process management: as a process manager, the OS handles creation & deletion of processes, suspension & resumption of processes, scheduling & synchronization of processes. Eg. Dead lock concepts.

2. Memory management – as a memory manager, the OS handles allocation & de-allocation of memory space as required by various programs. The major tasks include:

Ø  Relocation – loading from secondary storage to RAM

Ø  Protection  & sharing

Ø  Concept of virtual memory

3. File management – The OS is responsible for creation and deletion of files & directories. It also takes care of organizing, storing, retrieving, naming & protecting the files.

4.      Device management – The OS provides input/output subsystem between process and device driver. It handles the device caches, buffers and interrupts. It also detects the device failures and notifies the same to the user.

5.      Security management – The OS protects system resources and information against destruction and unauthorized use.

6.      User interface – The OS provides the interface between the user and the hardware. The user interface is the layer that actually interacts with the computer operator. The interface consists of a set of commands or menus through which a user communicates with a program.