The most common and most likely answer to this crossword clue is the 9 letter word MAINFRAME
I've seen this crossword clue in The Times
M
A
I
N
F
R
A
M
E
More clues leading to the result MAINFRAME
- Large computer suffering RAM famine?
- What you may see with photograph of mum and computer?
- Computer graduate pictured?
- Old lady with walker seen around in processing unit
- Most important to fit up computer
- Criminal mafia men run powerful computer
- Computer firm with a name that is unusual
- Computer master's at home with brother and me
Buddy explains!

The straight part
We know that "Large computer" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case large computer = mainframe.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does MAINFRAME mean?
MAINFRAME noun- A large, powerful computer able to manage very many simultaneous tasks and communicate with very many connected terminals; used by large, complex organizations (such as banks and supermarkets) where continuously sustained operation is vital