Damage memory, looking back (3)
I believe the answer is:
mar
'damage' is the definition.
(to mar is to spoil or damage)
'memory looking back' is the wordplay.
'memory' becomes 'ram' (Random Access Memory on a computer).
'looking back' says the letters should be written backwards.
'ram' in reverse letter order is 'MAR'.
(Other definitions for mar that I've seen before include "Blight" , "'Impair, spoil (3)'" , "Disfigure" , "Ruin" , "Detract from" .)