State ad must be prepared for computer file (4,3)
I believe the answer is:
data set
'computer file' is the definition.
(set of data on a computer)
'state ad must be prepared' is the wordplay.
'must be prepared' indicates an anagram.
'state'+'ad'='statead'
'statead' with letters rearranged gives 'DATA SET'.
'for' acts as a link.
(Other definitions for data set that I've seen before include "file" , "collected info" , "Collection of information (in computing)" .)