Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, development starting in the 1970s at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and others. 

Initially intended for use inside the Bell System, AT&T licensed Unix to outside parties from the late 1970s, leading to a variety of both academic and commercial variants of Unix from vendors such as the University of California, Berkeley (BSD), Microsoft (Xenix), IBM (AIX) and Sun Microsystems (Solaris). AT&T finally sold its rights in Unix to Novell in the early 1990s, which then sold its Unix business to the Santa Cruz Operation (SCO) in 1995, but the UNIX trademark passed to the industry standards consortium The Open Group, which allows the use of the mark for certified operating systems compliant with the Single UNIX Specification (SUS). Among these is Apple's macOS, which is the Unix version with the largest installed base as of 2014. 

From the power user's or programmer's perspective, Unix systems are characterized by a modular design that is sometimes called the "Unix philosophy", meaning that the operating system provides a set of simple tools that each perform a limited, well-defined function, with a unified filesystem as the main means of communication and a shell scripting and command language to combine the tools to perform complex workflows. Aside from the modular design, Unix also distinguishes itself from its predecessors as the first portable operating system: almost the entire operating system is written in the C programming language that allowed Unix to reach numerous platforms.

Based on the article and the following list of answers, write a list of questions.

1. Unix
2. a family of multitasking, multiuser computer operating systems
3. the original AT&T Unix
4. in the late 1970s
5. Yes
6. some are academic and others commercial
7. the University of California, Berkeley
8. (BSD)
9. Microsoft
10. (Xenix)
11. IBM  and Sun Microsystems
12. (AIX) and (Solaris)
13. Novell
14. in the early 1990s
15. Yes
16. 1995
17. SCO
18. Yes
19. the Santa Cruz Operation
20. Apple's macOS

Numbered questions:
1. what OS is the article about?
2. what is it?
3. where did it come from?
4. when did they let other work on their OS?
5. are there different versions?
6. how do they differ?
7. who released some versions?
8. what was their flavor named?
9. who else?
10. what did they call theirs?
11. anyone else?
12. what were their flavors named?
13. who bought the rights to from the phone company?
14. when?
15. did they resell it?
16. when?
17. who bought it?
18. is that an acronym?
19. what does it stand for?
20. as of 2014 which flavor has the largest install base?