Unix Operating System Overview

Study Notes

Unix is the most popular operating system developed in AT&T laboratories.
Unix source code is currently owned by THE OPEN GROUP.
The operating system has been used as a base by many vendors, who developed their own value-added versions.
Two distinct flavors (strains) of Unix emerged from its beginnings at AT&T Bell Laboratories: SYSTEM V and BSD (BERKELEY SOFTWARE DISTRIBUTION).
There was considerable cross-influence between them.

Fig. 1 illustrates the Unix genealogy based on the family.
A detailed Unix family tree can be found at http://perso.wanadoo.fr/levenez/unix/.
The opening chapters of Life with UNIX, by Don Libes and Sandy Ressler, provide an entertaining overview of the history of Unix.
A Quarter Century of UNIX, by Peter Salus, offers a detailed written history.

Linux is an open-source system kernel that forms the basis of various distributions designed to serve different purposes and environments.
Linux originated in 1991 as a personal project of Linus Torvalds, a Finnish graduate student.
The kernel was initially conceived as a modest offshoot of Minix, a model operating system written by Andrew S. Tanenbaum.
By exploiting the power of cooperative development, Linus was able to tackle a more ambitious agenda.
Kernel version 1.0 was released in 1994.

POSIX (PORTABLE OPERATING SYSTEM INTERFACE) is a family of standards specified by the IEEE for maintaining compatibility between operating systems.

System management involves a range of activities and requires both people skills and computer skills.
Table 1 shows personal experience of Æleen Frisch in Linux system administration.

SWAP is a space on a hard drive used as virtual memory when the physical RAM is full.
It allows the system to continue running applications by swapping out less frequently used data from RAM to SWAP space.
Windows OS has a similar concept known as the page file or virtual memory (located in C:\PAGEFILE.SYS).
The key difference between Linux and Windows SWAP is that Linux SWAP is usually a separate partition on the file system, defined and managed by the user/system administrator, whereas the Windows page file is located on the system drive and is managed automatically by the Windows OS.