Measure of processing speed for plate needing development (8)
I believe the answer is:
teraflop
'measure of processing speed' is the definition.
(measure of computer speed)
'for plate needing development' is the wordplay.
'needing development' indicates an anagram (letters developed in another way).
'for'+'plate'='forplate'
'forplate' is an anagram of 'TERAFLOP'.
(Other definitions for teraflop that I've seen before include "Measure of speed" , "able to work at high-speed" , "able to calculate fast" .)