The most common and most likely answer to this crossword clue is the 4 letter word UNIX
U
N
I
X
More clues leading to the result UNIX
- Low-level software returned each of consecutive letters
- Operating system that’s “superior” leading to nothing
- 7 academics and students cross
- Greek characters retire operating system
- Wife’s clothing reverse of fashionable, being OS?
- E.g. Oxford, second therefrom? I can handle data aplenty
- You finally delete operating system
- Detach, having lost core operating system
- Universal veto for operating system
- Education centre supported by variable software system
Buddy explains!

The straight part
We know that "Operating system" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case operating system = unix.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does UNIX mean?
UNIX noun- Any Unix-like operating system, including Unix.
- Collectively, Unix and unix-like operating systems.