The most common and most likely answer to this crossword clue is the 7 letter word GIGABIT
I've seen this crossword clue in The Guardian
G
I
G
A
B
I
T
More clues leading to the result GIGABIT
Buddy explains!

The straight part
We know that "PC unit" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case pc unit = gigabit.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 GIGABIT mean?
GIGABIT noun- 109 bits, a thousand million (1,000,000,000) bits.
- 230 (1,073,741,824) bits.