Types of computers, system software, concept of file, directory and folder

Classification of computer

  1. Computers are classified into five, they are microcomputer, minicomputer, workstation, mainframe computer and supercomputer
  2. Microcomputer – personal computer (eg : laptop), device used to scan code of products in supermarket
  3. Minicomputer is a small general purpose computers, have the capability to serve a number of users simultaneously
  4. Workstation is a single user desktop like personal computer, but i t have better processor and monitor display
  5. Mainframe computers are large in size and have very high speed, Eg : ATM
  6. Supercomputers are fastest and expensive, used for weather forecasting, statistical analysis etc..,

Basics of software

  • Software is a set of programs
  • Program is a collection of instructions
  • Program convert data in to information
  • Information is useful and intelligible form of data
  • Software is of two types – application software and system software
  • Application software is created for a specific task
  • System software is used to run application software, it also interface application software and hardware
  • Operating system is a good example of system software

concept of file

To create a file
a) allocate the space in file system
b) make an entry for new file in directory

  1. Three types of file system in an operating system – NTFS, FAT, FAT32
  2. File is an abstract data type
  3. File is logical storage unit
  4. File is usually non volatile
  5. There are six minimal file operations
  6. System supports two types of files, which are executable binary files and text files
  7. Two methods for access files are sequential files and direct access
  8. Simplest directory structure – two level directory, by this name collision can be avoided (which is the problem in one level directory)
  9. Two kinds of paths – absolute path and relative path
  10. In Tree structure sharing of files and directories are not possible,


Shared sub-directory and files are examples of Acyclic graph directory. Cycle is present in one level directory, two level directory, general graph directory, Lowest level of I/O control consist of device drivers and interrupt handlers

File identifier is used to identify file in the file system. Object file is a sequence of bytes organized into blocks understandable by the system’s linker. Mounting of file system – attaching portion of file system in to directory structure. Mapping of file is managed by file metadata. Mapping of network file system protocol to local file system is done by network file system. file system fragmentation occurs when unused space or single file are not contiguous. “Inode” represents files and directories

Important Points in File and Directory concept

  • Journaling is preferred for Faster file system recovery, exampleExt3.
  • ACL stands for Access control list
  • VFS Support multiple file system type
  • Buffer cache helps to Improve read/write performance
  • Wear leveling affects Flash
  • Superblock is the inode number of the first inode in the file system
  • Superblock shows size and shape of this file system
  • Superblock is number of free blocks in the file system
  • External fragmentation is solved by linked allocation and index allocation
  • Linked method is best available allocation method
  • Allocate the first hole which is big enough – first fit
  • Allocate the smallest hole which is big enough – best fit
  • Allocate the longest hole which is big enough – worst fit
  • First fit is faster memory allocation
  • In bit vector no free space list is implemented
  • In bit vector free space list is implemented as bit map or bit vector
  • In bit vector, if block is free bit is 1 other wise 0
  • In MS-DOS object have extension .OBJ and load modules have .EXE/.COM
  • File is also called data set
  • Backup should be done daily in every installation
  • VSAM file is relative record data set, keyed sequential data set, entry sequential data set
  • Relative organisation – file structure redefine its first record at a base of zero
  • File record length is chosen according to data characteristics
  • Increment backup saves files which are recently changed
  • Portioned data is used for a program or source library
  • In magnetic disk data is stored in tracks which are divided into sector
  • Block cache or buffer cache is used to improvise performance of disk
  • Context switching is part of interrupt handling
  • Boundary register track beginning and ending of program
  • Map table allows pages to locate
  • Data encryption mostly used in financial networks
  • Magnetic tape supports contiguous sequential file organisation
  • Variable depending upon the usage of the data set is most efficient data set organisation
  • Disaster recovery varies in degree between installations
  • Wild card specifiers – provide an easy way to find a group of related files
  • Allocation map specifies which blocks are used by which files
  • Smallest piece of data is called item
  • All keys to identify a particular item is different
  • Items in key field of record is called key

concept of file, directory and folder

DOS – Disk operating system

signal generator and distortion meter

For subject wise study materials  for bsnl je/tta  :





Basic electronics

Digital electronics