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What about all those "Flavors"?

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The Single UNIX Specification
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The UNIX Brand
What About All Those "Flavors"
Version 2 of the Single UNIX Specification
Version 3 of the Single UNIX Specification
UNIX 93 & UNIX 95
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Why This is Different

UNIX System Chronology
What about Linux?
What about BSDI?
What about IBM® 's OS/390
What about Windows® NT?
What about Digital® UNIX,   Hewlett Packard HP-UX®,   IBM AIX®,   SCO UnixWare®,   SGI IRIX®,   Sun Solaris® ?


Since it began to escape from AT&T's Bell Laboratories in the early 1970's, the success of the UNIX operating system has led to many different versions;  Universities, research institutes, government bodies and computer companies all began using the powerful UNIX system to develop many of the technologies which today are part of the IT environment. Computer aided design, manufacturing control systems, laboratory simulations, even the Internet itself, all began life with and because of UNIX systems.

Soon all the large vendors, and many smaller ones, were marketing their own, versions of the UNIX system optimised for their own computer architectures and boasting many different strengths and features. See the UNIX System Chronology graphic below.


UNIX Chronology
Click here to see the larger image

What about Linux?

Developed by Linus Torvalds, Linux is a product that mimics the form and function of a UNIX system, but is not derived from licensed source code. Rather, it was developed independently; by a group of developers in an informal alliance on the net. A major benefit is that the source code is freely available (under the GNU copyleft), enabling the technically astute to alter and amend the system; it also means that there are many, freely available, utilities and specialist drivers available on the net.

Recent versions of Glibc include much functionality from the Single UNIX Specification, Version 2 (for UNIX 98).

What about BSDI?

BSDI is an independent company that markets products derived from the Berkeley Systems Distribution (BSD), developed at the University of California at Berkeley in the 60's and 70's. It is the operating system of choice for many Internet service providers. It is, as with Linux, not a registered UNIX system, though in this case there is a common code heritage if one looks far enough back in history.

What about IBM®'s OS/390?

IBM has been quietly working on its mainframe operating system (formerly MVS) to add open interfaces for some years. In September 1996, The Open Group announced that OS/390 had been awarded the X/Open UNIX brand, enabling IBM to identify its premier operating system to be marked UNIX 95. This is a significant event as OS/390 is the first product to guarantee conformance to the Single UNIX Specification, and therefore to carry the label UNIX 95, that is not derived from the AT&T/ SCO source code.

What about Windows® NT?

Microsoft® Windows NT was developed as a completely new, state of the art, 32 bit operating system. As such, it has no connection with the UNIX system source code. However, market demand for POSIX.1 , POSIX.2 has led to developments by several companies of add-ons that provide partial functionality. Should the functionality meet the requirements of the UNIX brand then indeed it could become a registered UNIX system.

What about Digital® UNIX,   Hewlett Packard HP-UX®,  IBM AIX®,   SCO UnixWare®,   SGI IRIX®,   Sun Solaris® ?

These are all registered UNIX products. To see the full list of UNIX vendors and the current UNIX branded product register select here.


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The Open Group 1995-2002 Updated on Monday, 25 June 2001