In order to make the computer perform useful work for us, it is has to be ‘driven’ by means of programs – software – which specify the task to be done. The combination of hardware and software provide a total usable system.
An operating system is a program that acts as an intermediate between a user of a computer and the computer hardware. The purpose of an operating system is to provide an environment in which a user can execute programs. The primary goal of an operating system is thus to make the computer system convenient to use. A secondary goal is to use the computer hardware in an efficient manner.
A computer system can be divided roughly into four components the hardware, OS, application programs, and the users.
A computer system has many resources ( hardware and software ) that may be required to solve a problem; CPU time, memory space, file storage space, I/O devices and so on.
A slightly different view of an operating system focuses on the need to control the various I/O devices and user programs. An operating system is a control program. A control program controls the execution of user programs to prevent errors and improper use of the computer. It is especially concerned with the operation and control of I/O devices.
Sine bare hardware alone is not particularly easy to use,
application program are developed. These programs require certain common
operations, such as controlling the I/O devices. The common functions of
controlling and allocating resources are then brought together into one piece
of software i.e. the operating system.
Function of Operating System
An OS is a program that performs four basic functions.
1. Communicate, or at least provide a method for other programs to communicate, with the hardware of the PC. It’s upon the OS to access the hard drives, respond to the keyboard, and output data to the monitor.
2. OS must create a user interface – a visual representation of the computer on the monitor that makes sense to the people using the computer input devices, such as mice and keyboards, to enable users to manipulate the user interface and thereby make changes to the computer.
3. OS, via the user interface, must enable users to determine the available installed programs and run, use, and shut down the program of their choice.
4. OS should enable users to add, move, and delete the installed lrograms and data.
Operating System and BIOS
The hardware in a PC does not know the software. The BIOS is the interface between hardware and software. It is also a software but is called firmware due to its integration with hardware. Without BIOS, the pc is a dead machine.
On PC’s, the BIOS contains all the code required to control the keyboard, display screen, disk drivers, serial communications and a number if miscellaneous functions.
The BIOS 23is typically placed in a ROM chip that comes with the computer it is often called a ROM BIOS. This Ensure that the BIOS will always be available and will not be damaged by disk failure. It also Make it possible for a computer to boot itself. It is the BIOS which controls the hardware according to the requirement of the OS.
Many modern PCs have a flash BIOS, which means that the BIOS has been recorded on a flash memory chip, which can be updated if necessary.
Classification
An operating system is conceptually broken into the two component- A shell and a kernel. As the name implies the shell is an outer wrapper to the kernel which in turn talks directly to the hardware.
In some operating system the shell and the kernel are completely separate entities.
Kernel design ideologies include monolithic kernel, microkernel and exokernel. Among commercial system, Unix and Windows use the monolithic approach.
Types of Operating System
Single-user, single task : As the name implies, this operating system is design to manage the computer so that one user can effectively do one thing at a time. DOS is good example of a single-user, single-task operating system.
Single-user, multi-tasking : This is the type of operating system most people use on their desktop and laptop computers today. Windows and Mac OS are both examples of an operating system that will let a single user have several programs in operating at the same time.
e.g. it is possible for a windows user to be writing a note in a word processor while downloading a file from the internet while printing the text of an e-mail message.
Multi-user : A multi user operating system allows many different users to take advantage of the computer’s resources simultaneously. The OS must make sure that the requirement of the various user are balance, and that each of the programs they are using has sufficient and separate resources so that a problem with one user doesn’t affect the entire community of users. Windows, Linux and Mac OS are examples of multi-user Operating System.
