Datasheet
Unix Versions
In the early days Unix was made available as source code rather than in the typical binary form. This
made it easier for others to modify the code to meet their needs, and it resulted in forks in the code,
meaning that there are now many disparate versions (also known as flavors).
Source code represents the internal workings of a program, specifying line by line how a program or
application operates. Access to source code makes it easier to understand what is occurring in the pro-
gram and allows for easier modification of the program. Most commercial programs are distributed in
binary form, meaning they are ready to be run, but the internal lines of code are not readable by people.
There are primarily two base versions of Unix available: AT&T System V and Berkley Software
Distribution (BSD). The vast majority of all Unix flavors are built on one of these two versions. The pri-
mary differences between the two are the utilities available and the implementations of the file structure.
Most of the Unix flavors incorporate features from each base version; some include the System V version
utilities in
/usr/bin and the BSD version in /usr/ucb/bin, for example, so that you have the choice
of using a utility with which you are comfortable. This arrangement is indicative of the Unix way of
providing the flexibility to do things in different ways.
The various versions of Unix systems provide the user the power of choice: you can select the flavor that
best matches your needs or system requirements. This ability to choose is considered by many as a
strength, although some see it as a weakness in that these slightly differing versions and flavors create
some incompatibilities (in the implementation, commands, communications, or methods, for example).
There is no “true” version of Unix or one that is more official than others; there are just different imple-
mentations. Linux, for example, is a variant of Unix that was built from the ground up as a free Unix-like
alternative to the expensive commercial Unix versions available when Linux was first created in 1991.
Here are some of the more popular flavors of Unix available:
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Sun Microsystem’s Solaris Unix
IBM AIX
Hewlett Packard HP-UX
Red Hat Enterprise Linux
Fedora Core
SUSE Linux
Debian GNU/Linux
Mac OS X
KNOPPIX
Yellow Dog Linux (for Apple systems)
Santa Cruz Operations SCO OpenServer
SGI IRIX
FreeBSD
OpenBSD
NetBSD
OS/390 Unix
Plan 9
Each of these flavors implements its version of Unix in a slightly different way, but even though the
implementation of a command may vary on some systems, the core command and its functionality follow
the principles of one of the two major variations. Most versions of Unix utilize SVR4 (System V) and add
the BSD components as an option to allow for maximum interoperability. This is especially true with com-
mands; for example, there are two versions of the
ps command (for showing processes) available on most
systems. One version of
ps might reside in /usr/bin/ps (the System V version) while the other might
exist in
/usr/ucb/bin (BSD version); the commands operate similarly, but provide output or accept
optional components in a different manner.
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