Advanced Programming in the UNIX® Environment, Third Edition


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Frequently Asked Questions

  1. What is the difference between "UNIX System" and "UNIX system?"
  2. What is the difference between Unix and UNIX?
  3. Is Mac OS X a UNIX system?
  4. Is FreeBSD a UNIX system?
  5. Is Linux a UNIX system?
  6. Is Solaris a UNIX system?
  1. What is the difference between "UNIX System" and "UNIX system?"

When we speak of the UNIX System itself as an entity, we capitalize the 'S' in System. When we are speaking about a possible implementation of the UNIX System or a particular UNIX system, we use a lower-case 's'.

  1. What is the difference between Unix and UNIX?

The Unix operating system was developed at AT&T Bell Laboratories. When AT&T registered the name as a trademark, they capitalized the name to UNIX. Today the trademark is owned by The Open Group. For a system to call itself UNIX, it needs to meet certain criteria, pass conformance tests, and license the name.

  1. Is Mac OS X a UNIX system?

As of version 10.5, Mac OS X has been formally certified to be a UNIX system.

  1. Is FreeBSD a UNIX system?

While FreeBSD resembles a UNIX system and provides a UNIX-compatible environment, it has not yet been formally certified as a UNIX system. On the other hand, if it looks like a duck, walks like a duck, and quacks like a duck, then it's probably a duck.

  1. Is Linux a UNIX system?

While Linux resembles a UNIX system and provides a UNIX-compatible environment, it has not yet been formally certified as a UNIX system. On the other hand, if it looks like a duck, walks like a duck, and quacks like a duck, then it's probably a duck.

  1. Is Solaris a UNIX system?

Yes, Solaris has been formally certified to be a UNIX system.