Concept of Software
Software refers to a set of instructions that direct a computer on what to do. In order for a computer to process data, it is guided by a set of instructions known as programs (software).
Classification of Software
There are several ways of classifying computer software. These are:- according to purpose, acquisition and End-User-License (EUL)
Classification according to purpose
Under this classification software may be classified as either system software or application software.
System software.
System software enables users to communicate with the computer and its various devices such as the keyboard, the monitor, disk and printers. Basically system software perform the following functions
Booting the computer and making sure that all the hardware elements are working properly
Performing operations such as retrieving, loading, executing and storing application programs
Storing and retrieving files
Performing a variety of system utility functions
System software can be divided into four sub-categories
Operating systems
Firmware
Utility software
Networking software
Operating System (OS)
An operating system consists of a set of complex programs that work together to control execution of application programs and acts as an interface between the application and the computer hardware. It manages input, output and storage operations in a computer. Examples of common operating systems are Microsoft Windows (2000, XP, Vista, windows 7 and windows 8), UNIX, Linux and Macintosh (MacOS)
Firmware (Stored Logic)
Firmware is a combination of both the software and hardware recorded permanently on electronic chips. A firmware is a read-only-memory chip that is mounted or plugged into motherboard. Firmware may hold an operating system, utility programs, language processors etc.
Utility software
Utility software is a special program that performs commonly used services that make certain aspects of computing go on smoothly. Examples of important utilities that are accompanied in most operating systems include
File manager
Program manager Program translator Setting editor
Text editor
Graphics editor Sort utility
Calculator utility Time utility
Calendar utility Backup utility Recovery utility
Compress/decompress utility Defragment utility
Sound player utility Anti-virus utility
The internet browsing utility The help utility
Networking software
Networking software is mostly used to establish communication between two or more computers by linking them using a communication channel like cables to create a computer network.
Network software may come as independent software or integrated in an operating system.
Application Software
Application software (application packages) are programs that are designed to help the user to accomplish specific tasks. Examples and uses of common application packages
Classification according to acquisition
In this classification, software are divided into in-house developed and vendor off-the-shelf software
In-house developed software
These are programs that are specially designed to meet a particular user’s needs. These programs are not available in the shops.
Vendor off-the-shelf software
These are software developed by software engineers, packaged and then made available for purchase through a vendor, a distributor or directly from the developer. A developer may bundle more than one but closely related software into one package to form a suite or integrated software. Examples are Lotus Suite, Microsoft Office and Corel WordPerfect
Classification according to End-User-License
Software classified according to End-User-License include Open Source, Proprietary and Freeware
Open Source software
Open source software refers to software whose source code is freely made available to users. The users are encouraged to use, modify and distribute the modified product. Linux operating systems and OpenOffice are open source software which are made available to users under General Public License (GPL)
Proprietary software
Proprietary software are those software whose source code is hidden from users. Modifications are only made by the software manufacturers. Examples include Microsoft Windows Operating System, Microsoft Office, Adobe PageMaker and CorelDraw Suite
Freeware software
Freeware are software products that are freely made available to the user. A good example is Grisoft antivirus software known as AVG Free Edition
OPERATING SYSTEM
An operating system (OS) is software that manages computer hardware and software resources and provides common services for computer programs.
It is a group of computer programs that coordinates all the activities among computer hardware devices. It is the first program loaded into the computer by a boot program and remains in memory at all times. The operating system is an essential component of the system software in a computer system. Application programs usually require an operating system to function. Without an operating system computer hardware and application programs would be useless.
Types of Operating Systems (OS)
Operating systems can be classified according to:-
Number of tasks
Number of users
User interface
Classification according to number of tasks
Single task operating system
Single program operating system allows processing of one application program in the main memory at a time. Therefore a user must exit from the program before loading and running another program. An example of a single user operating system is MS DOS.
Multitasking operating system
Multitasking operating system is an operating system that is capable of allowing multiple software processes to run at the same time. Examples of operating systems that would fall into this category are: Linux, UNIX, and Windows 7.
Classification according to number of users
Single-user operating system
A single user operating system is designed to be used by only one person. It cannot support more than one person and runs only one user application program at a time
Multi-user operating system
Multi-user or multi-access operating systems allow more than one user to interactively use a computer. Examples of multi-user OS include Windows 2003 server, UNIX, Novell, Linux and Windows NT/2000.
Classification according to interface
Command-line based operating systems
Command-line user interface operating systems lets the user type a command at a prompt command. A user is required to type character-based commands such as PRINT, COPY, or INPUT into the computer using the keyboard. Unique abbreviations can also be used, for example DEL, REN, CHKDSK etc.
For example if you are using MS DOS, you can delete a file called myfile.doc that is located in a directory called Letters on the disk drive called C as follows DEL C:\Letters\myfile.doc
Command-line operating systems are in small use today because it is difficult to remember the commands, cannot process complex graphics and difficult to make use of emerging hardware and software technologies.
Menu driven interface
Menu driven interfaces provide the user with a list of options to choose from. To select a program to run a user either types the number of the program or presses the function with that number. Instructions on whether to type a number or press a function key to choose an option are provided by a program.
Graphical User Interface (GUI)
GUI is the latest and more user-friendly interface. It is a computer program that enables a person to communicate with a computer through the use of symbols, visual metaphors, and pointing devices. A GUI uses WIMP which stands for Window, Icons, Menus and Pointing devices to carry out commands, such as opening, deleting, and moving files.
Although many GUI operating systems are through the use of a mouse, the keyboard can also be utilized by using keyboard shortcuts or arrow keys.
Unlike a command line operating system like UNIX or MS-DOS, GUI operating systems are much easier to learn and use because commands do not need memorized. Additionally, users do not need to know any programming languages. Because of their ease of use, GUI operating systems have become the dominant operating system to most end-users.
Basic Components of a GUI
Graphical user interfaces, such as Microsoft Windows and the one used by the Apple Macintosh, have the following basic components:
Pointer : A symbol that appears on the display screen and that you move to select objects and commands. Usually, the pointer appears as a small angled arrow.
Text -processing applications, however, use an I-beam pointer that is shaped like a capital I.
Pointing device : A device, such as a mouse or trackball that enables you to select objects on the display screen.
Icons : Small pictures that represent commands, files, or windows. By moving the pointer to the icon and pressing a mouse button, you can execute a command or convert the icon into a window. You can also move the icons around the display screen as if they were real objects on your desk.
Desktop : The area on the display screen where icons are grouped is often referred to as the desktop because the icons are intended to represent real objects on a real desktop.
Window: You can divide the screen into different areas. In each window, you can run a different program or display a different file. You can move windows around the display screen, and change their shape and size at will.
Menus : Most graphical user interfaces let you execute commands by selecting a choice from a menu.
Functions of an operating system
The basic functions of an operating system are:
Processor scheduling
Processor scheduling refers to allocating each job waiting for execution processor time at each given interval. Sometimes computer may have concurrent processes ready to be executed; therefore the OS determines which task to be processed first. The operating system schedules tasks according to priorities
Resource allocation
Resources of the computer include all facilities required by the computer in order to carry out tasks. The resources include time, main memory (RAM), permanent memory (disk, tape or CD-ROM drives) input devices, output devices and media.
Each resource available in a computer is given a unique identification number called an Interrupt Request (IRQ). The OS uses the IRQ to identify the resource being requested. Poor resource allocation may result to a deadlock. A deadlock is a situation where a particular job holds a requested resource and fails to release it, yet it is requesting for a resource held by another job.
Memory management
The OS ensures that each program and the data it requires are allocated adequate space in the RAM. Since the RAM is a scarce resource, the OS determines which task remains in memory waiting for execution and which one will be kicked out back to secondary storage.
The OS organizes the Main Memory into blocks of sizes called page frames, and then processes are equally divided into pieces that can fit into the frames called pages. To manage the memory the OS swaps pages between the main memory and secondary storage.
Input/output management
The operating system ensures that transmission and reception of signals between the CPU and Peripheral devices are correct and secured. In this case the OS coordinates between these various Input/output and other peripheral devices such as auxiliary storage devices ensuring that data is transmitted securely.
Communication control and management.
The OS manages various communication devices and provide an environment within which communication protocols operate. Protocol refers to the rules that govern communication between devices on a network.
Error handling
The OS tends to alert the user about the errors that may arise due to illegal operations, hardware and software failure. Most operating systems express what the error is and where possible make suggestions on how to correct the error.
Interrupt handling
An interrupt is a break from the normal sequential processing of instructions in a program. As soon as the status of a running task changes, the OS will immediately inform the operator.
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