General Background

Unix Flavors

People new to Unix are sometimes a little confused about the different names they hear used. People frequently ask "What's the difference between Unix and Solaris and Linux?" The short answer is "for most users, not a great deal". All of todays varieties of Unix are offspring from the original Unix operating system created at Bell Labs. Over the years, specific universities and computer vendors made their own modifications to the Unix source code to (hopefully) make the operating system run more efficiently (and faster) on their proprietary hardware. When the vendors sold their hardware, they also distributed (sometimes referred to as "bundled") their modified version (or flavor) of Unix. All flavors of Unix share basic features, which is an essential concept for the end user to understand. Several modern flavors of Unix are listed below.

Originator	Proprietary Name ¹
U. Cal. Berkley	BSD
Sun	Solaris
IBM	AIX
HP	HP-UX
SGI	IRIX
Digital Equipment ²	DEC Unix
Compaq	Tru64 Unix ³
Apple	MacOS X ⁴
L. Torvalds/GNU ⁵	Linux ⁶

¹ All proprietary Unix flavors and their names are respective trademarks of the originating entity/vendor.

² Digital Equipment Corp. (DEC) is no longer a corporate entity since being acquired by Compaq in 1998. Compaq then "merged" with Hewlett-Packard (HP) in 2001.

³ Compaq acquired DEC Unix in its acquisition of DEC, and renamed this Tru64 Unix, which now belongs to HP. However, both the DEC Unix and the Tru64 Unix flavors of Unix are still in use.

⁴ Mac OS X is an offspring from a BSD parent.

⁵ This is not the place to put on the gloves and settle which group provided what.

⁶ Pronounced lih-nuhks with a short "i".

As Operating System portability became a focal point, several flavors of Unix were "ported" to multiple hardware platforms. For example, Sun's Solaris will run on PC's as well as Sun's proprietary hardware. It is interesting to note at this point that Linux is a non-proprietary flavor of Unix that has been ported to a plethora of different types of hardware devices, not just computers (e.g. PDA's, cell phones, digital video devices such as TiVo, gaming consoles, etc.)

What is important for the Unix end-user to keep in mind is that most basic (core) commands are similar (and most likely identical) on most Unix systems.

Unix Features

The Unix Operating System has a number of features that account for its flexibility, stability, power, robustness and success. Some of these features include:

Unix is a multi-user, multi-tasking Operating System, which allows multiple users to access and share resources simulaneously (i.e. concurrently).

The Unix OS is written in a modern, high-level programming language, specifically the C programming language. This makes it easy for programmers to read and modify the Unix source code, and more importantly, port¹ this source code to other types of hardware. This accounts for its presence on a very wide range of computer hardware and other devices. Prior to being written in C, the Unix OS was written in assembly language, as were most, if not all computer Operating Systems of the time.

Unix hides the details of the low-level machine architecture from the user, making application programs easier to port to other hardware.

Unix provides a simple, but powerful command line User Interface (UI).

The user interface provides primitive commands that can be combined to make larger and more complex programs from smaller programs.

Unix implementations provide a hierarchical file system, which allows for effective and efficient implementation while providing a solid, logical file representation for the user.

Unix provides a consistent format for files, i.e. the byte stream, which aids in the implementation of application programs. This also provides a consistent interface for peripheral devices.

Students sometimes remark "so what, don't all operating systems provide these features?" The simple answer to this is No! Not all modern operating systems provide the stability, flexibility, and power these features provide in Unix. So you don't believe me...ask yourself when was the last time you had to reboot your computer?

Another example of an OS lacking the aforementioned features is Apple Computer's Mac OS 9 (and earlier versions). Apple apparently could not create an OS with this stability and robustness, so they ported Unix to the Mac and named it Mac OS X.²

¹ To port software means to move the original source code to a different hardware device (e.g. a different computer), modify the code as necessary, re-build the execuatble image (i.e. re-compile/link the source), and have the program provide the same services with the same reliability as on the original machine.

² See: Mac OS X

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