COMPUTER VIRUS

A computer virus is a program written to do a specific task or an unusual
task, such as deleting files with a specific extension deleting data in the hard disk,etc c.i.h ,LOVE BUG,

Virus can spreads through followng:
i )internet 
ii)Network
iii)E-mail
iv) disketts


How to avoid or clean the virus
To avoid virus form entring your machine or if your computer is 
effected with virus you can use software known as'anti-virus software'to clean the virus

Main Components of a personal computer

physical data storage
since the main storage is relatively expensive it is used only to store data & program instrucations currently oprated main stroage is volatile in oder to store data and program files not currently being operated,but which have to be transferred to the main stroage when required we hawe permanently store them externally,and for this purpose backing storage auxiliary strage & secondary stirage secondary storage can be can be classified inti two main types

offline-the use of removable computer media such as a magnatic tapes & tape cartridges.Data not redily accessible to the cpu

magnetic tape drive &magnatic tape
as a secondry stroage medium magntic tape was very popular with mainframe computers in the past traditionallly it is of 1/2 width and the lenth varies depending on the size of the reel.now the cartidge foem of magnatic tape is becomong more popular because it is easy to use more compact and high capacity and data tranfer trate can vary form 100000 to1250000 characters per secound.this system is now is hardly used

online-storage system are physically connected to and controlled by the central prcessing unit with immediate access capability
manetic disk is the most popular on-line secondary storage medium with computers to day the machines that record and retrieve data on magnatic disk are known as disk drives disk drives like disks are of diferent size and capacities the oprating principles however are generally similar for all disk drives both hard and floppy the differences are primarily one precision,speed,and capacity
Conventional file system Evolution data base system
 before the advent of data base system it was common to customize file for each software application  howewer as an organizaion,s software application grew the separate files  created by each department to hold same data in diffrent formats caused duplication of data

file processing
a}updating: when data on the master record data base record is changed to reflect the current position
b}Referencing: file interrogation or file inauiry whenacssess is made to a particular record to asceratain what the content is note that this does not involve any alteration to the record itself
 c}file data base main activites are add record change one or mare data fileds and delete record'these particular activities come under the heading of maintaining the file data base
d}file sort-in data base system there is a requirement
e}file data base merage
f}file data base back-up -a copy of a file /data base is created for security purpose
g}file data reorganization-discussion