UNIX, written by Ken Thompson at Bell Laboratories in 1969, is the result of an attempt to create an operating system with an environment which would be simple for users. ``The UNIX kernel, the heart of the operating system" was written in C by Thompson and Dennis Ritchie four years later in order to produce a portable version of the operating system. Portable means the code was not specifically written for one type of machine only.[Abrahams]
Some UNIX architecture terms which may be useful to know are kernel, shell, and user interface. The kernel, or main operating system, schedules the Central Processing Unit, or C.P.U., and allocates hardware resources. The shell calls different system utilities in response to a user's request. The user interface is the method of communication between the user and the operating system. This may include keyboard, mouse, or monitor screen.
There are various flavors of Unix available The most common ones are based on SVR4 (System 5 Release 4) from AT&T (now Unix Systems Laboratory). For example, Sun Solaris 2.x, SGI IRIX, IBM AIX and HPUX are based on SVR4. Another version of Unix is 4.3 BSD (Berkeley Software Distribution) on which the Sun OS 4 operating system was based. This guide is written as a generic platform independent introduction to SVR4 Unix. Some important differences from BSD Unix are noted. However, because there are often small differences between the Unix operating systems on different computer systems, the definitive reference should always be the online manual pages (see Section 1.7).