Actually, none of GNU comes from UNIX. UNIX was proprietary software (and still is), so using any of its code in GNU would have been illegal. This is not a coincidence; this is why we developed GNU: since you could not have freedom in using UNIX, or any of the other OPERATING systems of the day, we NEEDED a free system to replace it. We could not copy programs, or even parts of them, from UNIX; everything had to be written afresh.

No code in GNU comes from UNIX, but GNU is a Unix-compatible system; therefore, MANY of the ideas and SPECIFICATIONS of GNU do come from UNIX. The name “GNU”, which stands for “GNU's Not Unix”, is a humorous way of giving credit to UNIX for this, following a hacker tradition of recursive acronyms that started in the 70s.

The first such recursive acronym was TINT, “TINT Is Not TECO”. The author of TINT wrote another implementation of TECO (there were already many of them, for various systems), but instead of calling it by a dull name like “somethingorother TECO”, he thought of a clever amusing name. (That's what hacking means: playful cleverness.)

Other hackers enjoyed that name so much that we imitated the approach. It became a tradition that, when you were writing from scratch a program that was similar to some existing program (let's imagine its name was “Klever”), you could give it a recursive acronym name, such as “MINK” for “MINK Is Not Klever.” In this same spirit we called our replacement for Unix “GNU's Not Unix”.

Historically, AT&T which developed Unix did not want anyone to give it credit by using “Unix” in the name of a similar system, not even in a system 99% copied from Unix. AT&T actually threatened to sue anyone giving AT&T credit in that way. This is why each of the various modified versions of Unix (all proprietary, like Unix) had a completely different name that didn't include “Unix”.

Actually, none of GNU comes from UNIX. UNIX was proprietary software (and still is), so using any of its code in GNU would have been illegal. This is not a coincidence; this is why we developed GNU: since you could not have freedom in using UNIX, or any of the other operating systems of the day, we needed a free system to replace it. We could not copy programs, or even parts of them, from UNIX; everything had to be written afresh.

No code in GNU comes from UNIX, but GNU is a Unix-compatible system; therefore, many of the ideas and specifications of GNU do come from UNIX. The name “GNU”, which stands for “GNU's Not Unix”, is a humorous way of giving credit to UNIX for this, following a hacker tradition of recursive acronyms that started in the 70s.

The first such recursive acronym was TINT, “TINT Is Not TECO”. The author of TINT wrote another implementation of TECO (there were already many of them, for various systems), but instead of calling it by a dull name like “somethingorother TECO”, he thought of a clever amusing name. (That's what hacking means: playful cleverness.)

Other hackers enjoyed that name so much that we imitated the approach. It became a tradition that, when you were writing from scratch a program that was similar to some existing program (let's imagine its name was “Klever”), you could give it a recursive acronym name, such as “MINK” for “MINK Is Not Klever.” In this same spirit we called our replacement for Unix “GNU's Not Unix”.

Historically, AT&T which developed Unix did not want anyone to give it credit by using “Unix” in the name of a similar system, not even in a system 99% copied from Unix. AT&T actually threatened to sue anyone giving AT&T credit in that way. This is why each of the various modified versions of Unix (all proprietary, like Unix) had a completely different name that didn't include “Unix”.