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UNIX ( [#!Troy90!#], [#!Sobell91!#]) is an operating system originating at AT&T Bell Labs in the 1970s. UNIX was one of the first operating systems written in the high level language, C, and intended to be machine hardware independent. Many versions of UNIX exist and the influence of UNIX on other operating systems is dramatic.

Versions of UNIX included virtual memory, multi-processing, symmetric multi-processor, a file system, networking, the X windowing systems, and a script-based user interface shells. Many versions of UNIX are free or near free and the source code is readily available.

UNIX is very popular in university and research environments because of the low cost, advanced features, and readily available source code. A large customer community has contributed massive number of applications, free for the asking. The UNIX distribution includes thousands of user applications.

The key architectural feature that has allowed UNIX to last for such a long time is the communication subsystem design. Everything in the communication subsystem has an index entry called the inode. Given an inode entry, an application can read and write bytes of data. The inode entry may be associated with a network, file system, a process, or a keyboard. Inodes give UNIX applications hardware I/O device independence and allows for dynamic redirection of I/O. A new I/O device is easy to install. Just create an inode, write a device driver, and almost like magic, a new I/O device is now on the system.

See tables 7.15 and 7.16 starting on page [*].

Table 7.15: Survey Part 1: Basic Properties UNIX
Question Response
Analysis? none..poor..fair.. good..great
Design? none..poor..fair..good.. great
Implementation? none..poor..fair..good.. great
Testing? none..poor..fair.. good..great
Cycles of ADIT? one..few..several.. frequent
Priority? no..yes
Versions? no.. yes
Change Order Control? no..yes
Internal Prototype? no.. yes
External Prototype? no.. yes
Alpha Release? no.. yes
Beta Release? no.. yes
Duration? 30 years
Effort? greater than 10,000 person years

Table 7.16: Survey Part 2: Change Control UNIX
Question Response
Did a new introduced requirement ever negatively affect accomplished work? never.. seldom..often..frequent
Did an architectural change ever negatively affect accomplished work? never.. seldom..often..frequent
Are new features introduced up to product release? never.. seldom..often..frequent
Is there a dedicated period of quality assurance before the product is released? no.. yes

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Ronald LeRoi Burback