Main computer network limited by storage space (8)
I believe the answer is:
atlantic
'main' is the definition.
(Atlantic is an example)
'computer network limited by storage space' is the wordplay.
'computer network' becomes 'LAN' (abbreviation for local-area network).
'limited by' indicates putting letters inside (limit can mean to contain or border off).
'storage space' becomes 'attic' (an attic may be used as storage space).
'lan' going within 'attic' is 'ATLANTIC'.
(Other definitions for atlantic that I've seen before include "Ocean from Arctic to Antarctic" , "Big sea" , "Latin cat found, strangely, in the ocean" , "What lies to the east of 10" , "New Jersey resort" .)