Unix is a modular OS made up of a number of essential components, including the kernel, shell, file system and a core set of utilities or programs.
At the heart of the Unix OS is the kernel, a master control program that provides services to start and end programs. It also handles low-level operations, such as allocating memory, managing files, responding to system calls and scheduling tasks. Task scheduling is necessary to avoid conflicts when multiple programs attempt to access the same resource at the same time. We turn to some examples of modern UNIX system
System V Release 4.0 was announced on October 18, 1988 and was incorporated into a variety of commercial Unix products from early 1989 onwards.A joint project of AT&T Unix System Laboratories and Sun Microsystems, it combined technology
SVR4 draws on the efforts of both commercial and academic designers and
was developed to provide a uniform platform for commercial UNIX deployment. It has succeeded in this objective and is perhaps the most important UNIX variant. It incorporates most of the important features ever developed on any UNIX system
BSD
The Berkeley Software Distribution or Berkeley Standard Distribution[1] (BSD) is a discontinued operating system based on Research Unix, developed and distributed by the Computer Systems Research Group (CSRG) at the University of California, Berkeley. The term "BSD" commonly refers to its open-source descendants, including FreeBSD, OpenBSD, NetBSD, and DragonFly BSD.
One of the most widely used and best documented versions of BSD is FreeBSD. FreeBSD is popular for Internet-based servers and firewalls and is used in a number of embedded systems. The latest version of the Macintosh OS, Mac OS X, is based on FreeBSD 5.0 and the Mach 3.0 microkernel
SOLARIS 10
Solaris is Sun’s SVR4-based UNIX release, with the latest version being 10. Solaris
provides all of the features of SVR4 plus a number of more advanced features, such
as a fully preemptable, multithreaded kernel, full support for SMP, and an objectoriented interface to file systems. Solaris is the most widely used and most successful
commercial UNIX implementation.
