Computer Notes- Operating System

An operating system consists of a set of programs that controls, coordinates and supervises the activities of distinctive components of a computer system. Its function is to establish a link between the computer hardware and the user. 
"An operating system is a software, or a series of programs, which performs various types of functions in order to manage and organize files." 

Some of the most commonly used operating systems are MS DOS, WINDOWS, LINUX, SOLARIES, CP/M etc. Operating system can be classified as follows Multi-user: It allows two or more users to run programs at the same time. Some operating systems permit hundreds or even thousands of concurrent users. Multi-tasking: It enables more than one program to run concurrently. Multi-processing: It supports running a program on more than one CPU. Multi-threading: Allows different parts of a single program to run concurrently. Real-time Processing: Responds to input instantly. They are used to control machinery, scientific instruments and industrial systems, general-purpose operating systems, such as DOS and UNIX are not real-time processing.

 Controlling the execution of various programs.
 Managing devices (like storage and retrieval of files on the disks).
 Process Management
 Memory Management
 Input/Output Management
 Information Management
 User Interface

 The term DOS stands for Disk Operating System developed by Microsoft for micro computers.
 DOS is a single user operating system.
 It has a Character User Interface (CUI) i.e., communication between a computer and the user is through characters.
 In DOS, one has to key in the commands on the prompt. Prompt is a place where commands are issued. It may look like
C:\> or C:\WINDOWS\>

File Extensions Meaning
.EXE- Executable Files
.COM- Command Files
.BAT- Batch Files
.DOC- Document Files
.TXT- Text Files
.PRG- Program Files
.OVR- Overlays
.SYS- System Files

 They are actual operating systems on their own.
 The previous versions of windows use DOS as the operating system and adding a graphical user interface which will do the multitasking.
 Windows 95 operating system can take advantage of the 32 - bit processors.

 Windows Me stands for Windows Millennium Edition.
 It is an upgrade of windows 98 released in 14 September, 2000.
 The system resources required for this operating system are significantly higher than previous versions of windows.
 It stands for Windows New Technology.
 It is an operating system for client-server type networks.
 The latest version of NT has a user interface that is practically identical to Windows 95.
 Windows NT has higher demands for the disk space and memory.
Recent windows versions are windows 7,windows 8, windows 8.1, windows 10 (launched in 2015)

 It is a multi-tasking operating system.
 It was a first graphical interface to achieve commercial success.
 Apple products are of high quality and always more expensive than comparable products.
 The current version is Mac OS X; which is version 10.

 UNIX is an operating system developed by Bell Labs to handle complex scientific applications.
 It is a multi-user and multi-tasking operating system.
 It is a command line interface.
 X-windows is a graphical interface for UNIX that is easier to work with than windows 98.

 Linux is an operating system similar to UNIX that is becoming more and more popular.
 It is an open source program created by Linux Torvalds at the University of Finland.
 Open source program means that the underlying computer code is freely available to everyone.
 The programmers can work directly with the code and add features.

Utility-programs perform tasks related to the maintenance of our computer's health - hardware or data.

 These programs make it easier to manage our files.
 Many programs are written to help the user find files, create and organize directories, copy, move and rename files.
 The newer graphical interfaces that come with operating systems like Windows 95 have reduced the need for alternate file management programs.

 These programs involve formatting and defragmenting disks.
 Defragmenting means putting files on the disk so that the whole file is in sequence.
 These programs reduce the time to access the file.

 It handles where the programs put their current data in RAM.
 They move certain memory-resident items out of the way.
 They increase the memory available by getting all the unused pieces together in one spot making a useable amount.

 It restores the backed up data.
 It compresses the data to take up the least space.

 They are must have programs.
 They monitor the computer for the activity of viruses.
 Viruses are nasty little programs that copy themselves to other disks to spread to other computers.