Interesting Facts, Information And Updates About World

FILE SYSTEM A file is an object on a computer that stores data, information, settings, or commands that are used with a computer program.  All of the files in the UNIX file system are organized into a multi-leveled hierarchy called a directory tree. UNIX File System is organized in tree structure. File tree can be arbitrarily deep.   File name must not longer than 256 characters. Single path name must not longer than 1023 characters. ORDINARY OR REGULAR FILES A large majority of the files found on UNIX and Linux systems are ordinary files. Ordinary files contain ASCII (human-readable) text, executable program binaries, program data, and more. DIRECTORIES A directory is a binary file used to track and locate other files and directories. The binary format is used so that directories containing large numbers of filenames can be search quickly. DEVICE (SPECIAL) FILES Device or special files are used for device I/O on UNIX and Linux systems. They appear in a file system just like an ord

What is UNIX? UNIX is an operating system which was first developed in the 1960s. It is a stable, multi-user, multi-tasking system for servers, desktops and laptops. UNIX systems also have a graphical user interface (GUI) similar to Microsoft Windows which provides an easy to use environment. However, knowledge of UNIX is required for operations which aren't covered by a graphical program, or for when there is no windows interface available. First version of UNIX developed at the University of California Berkeley. The UNIX Operating System The UNIX operating system is made up of three parts:  1. The kernel 2. The shell 3. Utilities  THE KERNEL • The kernel of UNIX is the hub of the operating system. • It allocates time and memory to programs and handles the filestore and communications in response to system calls.  THE SHELL Shell is the command line interpreter.  Shell is just another program  A program or command which i nteracts with the kernel and it may be any of: built-in sh

Vectored Interrupt: In vectored interrupts, the manufacturer fixes the address of the ISR to which the program control is to be transferred. the processor automatically branches to the specific address in response to an interrupt.  • The TRAP, RST 7.5, RST 6.5 and RST 5.5 are vectored interrupts. Non-Vectored Interrupt:   But in non-vectored interrupts the interrupted device should give the address of the interrupt service routine (ISR).    • The INTR is a non-vectored interrupt. Hence when a device interrupts through INTR, it has to supply the address of ISR after receiving interrupt acknowledge signal. Maskable & Non-Maskable Interrupt: The hardware vectored interrupts are classified into maskable and non-maskable interrupts.  • TRAP is non-maskable interrupt.  • RST 7.5, RST 6.5 and RST 5.5 are maskable interrupt. Masking is preventing the interrupt from disturbing the main program. When an interrupt is masked the processor will not accept the interrupt signal. The interrupts ca

What is Interrupt and how it is generated? Interrupt is a signal send by an external device to the processor, to the processor to perform a particular task or work. In the microprocessor based system the interrupts are used for data transfer between the peripheral and the microprocessor. When a peripheral is ready for data transfer, it interrupts the processor by sending an appropriate signal to the interrupt pin of the processor. If the processor accepts the interrupt then the processor suspends its current activity and executes an interrupt service subroutine to complete the data transfer between the peripheral and processor. After executing the interrupt service routine the processor resumes its current activity. This type of data transfer scheme is called interrupt driven data transfer scheme. Types Of Interrupt: The interrupts are classified into software interrupts and hardware interrupts. • The software interrupts are program instructions. While running a program, if a software

  Implementation   Stage: User training, File / System conversion Key Question: What is actual operation? Are user manuals ready? Are there delays in loading files? Results: Training programs, user friendly documentation  • It is concerned with user training, site preparation and file conversion. • When system is linked to terminal or remote sites it also includes telecommunication network and network testing along with system. • During final testing user acceptance is tested followed by user training, • System testing checks the readiness and accuracy of system to access, update and retrieve  data from new files. • If testing is successful program is run with live data or else a diagnostic procedure is use to locate and correct errors. Post-Implementation and Maintenance Stage: Evaluation, maintenance and enhancements. Key Questions: is system running? Should system be modified? Results: User requirements need, satisfied user. • There is an aging process require periodic mainten

Analysis Stage: Detailed evaluation of present system data collection. Key Question: What must be done to solve the problem? what are the facts? Result: Logical model of system. Ex: Data flow diagram, data dictionary. • Analysis is a detailed study of various operations performed by a system and their relationships within and outside of the system. • One aspect of it defining the boundaries of system and determining weather or not the system should consider other related system. • Data is collected in available files during analysis. • Interview is commonly used tool in analysis. It requires special skills and sensitivity to the subject. • Training, experience and common sense are required for collecting needed information to do analysis. • After analysis analyst has firm understanding of what is to be done. Design Stage: General design specification, detailed design specification, program construction and testing (output, input, files, procedures) Key Question: In general, how mu