The spade work for UNIX began a AT and T bell Laboratories in 1969 by Ken Thompson and and Dennis Ritchie. The OS was initially know as UNIX. In 1970 unics finally become UNIX. In 1973, UNIX was rewrite in 1973 in C principally author by Ritchie.
The kernel is the heart of the system a collection of programs write in C that directly communicate with the hardware there is only one kernel for any system. Its that part of system that is load into memory when the system is boot it manage the system resources; allocates time between user and processes, desides processes priorities and performs all the tasks. The kernel is traditional patiance is often call as the operating system.
The shell on the other hand, is the sleeping beauty of UNIX; it is actually the interface between the user and the kernel. The shell is the agency which takes care of the features of redirection; and has a programming capability of its own.
To be tools ans applications consist of application software, compilers, database, pakage, internet tools, UNIX commands.
File System –
All files in system are related to one another. The file system of UNIX resembles a tree that grows from top to bottom as shown in the figure. The file system begins with a directory called root at the top. The root directory is denote by slash(/), branching from root there are several directories such as bin, lib, etc.
tmp, dev each of these directories contains several sub-directories and files.
Multi-user system – Multi user system capability of UNIX allows several users to use the same computers to perform their tasks. Several terminals [key-words and monitors] are connected to a single powerful computer [UNIX server] and each user can work with system.
Multi-tasking system – Multi-tasking system is the capability to the operating system; to perform various task simultaneously. i.e. user can run multiple task concurrently.