The most common and most likely answer to this crossword clue is the 11 plus 4 letter word ACCELERATOR CARD
A
C
C
E
L
E
R
A
T
O
R
C
A
R
D
Buddy explains!
The straight part
We know that "Performance booster for PC" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case performance booster for pc = accelerator card.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.