25-08-2017, 09:32 PM
History of Unix
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Unix Philosophy
Easy to program by combining small building blocks
Not (naive) user friendly
A clean minimal design (nothing extra, nothing unnecessary)
Open access:
Provide tools and mechanism to combining the tools
Minimal restrictions to the ways of doing things
A user can be very creative (and frustrated).
Major Unix OS features:
Kernel
Shell
File System
Kernel
Manages memory and allocates it to each process
Schedules work done by the CPU
Organizes transfer of data from one part of machine to another
Accepts instructions from shell and carries them out
Enforces access permission on the file system
File System
Logical method for organizing and storing large amounts of information.
Easy to manage.
File: basic storage unit.
Types:
ordinary file (stores info)
directory (holds other files and directories)
special file (represents physical devices like printers, terminals, etc)
pipe (temporary file for command linkage)
UNIX: Multi-user Multi-tasking
More than one user can run at the same time and more than one task can run at the same time
Unix is multiuser multitasking, Window NT is, Windows is not.
In Unix, each program is starteBourne Shell: the default shell (sh)
original unix shell
does not have interactive features of newer shells
widely used for writing shell scripts
standard on Unix System V
C Shell (csh): available on BSD Unix and most other systems
with syntax similar to the C language
with many enhancement over the Bourne shell.
File Systems and the I-nodes
Each disk drive contains one or more file systems
Each file system occupies a number of cylinder groups.
Each file system has a superblock, an i-node table and files
The superblock is at a fixed location relative to the beginning of the file system. It contains a description of the file system.
One can find the location of the I-node table thru superblock.
Each entry of the I-node table is an I-node, which uniquely represents a file in the file system.