Old boy has computer paper (8)
I believe the answer is:
observer
'paper' is the definition.
(I've seen this before)
'old boy has computer' is the wordplay.
'old boy' becomes 'ob'.
'has' is a charade indicator (letters next to each other).
'computer' becomes 'server'.
'ob'+'server'='OBSERVER'
(Other definitions for observer that I've seen before include "organ on Sunday" , "One watching attentively" , "'Onlooker, spectator (8)'" , "I notice" , "Non-participant; a paper" .)