The donation will be phased as matching funding is received and will enable the Museum to begin a comprehensive refurbishment to accommodate more visitors and exhibits.
The museum already houses the world’s largest selection of working historic computers including the rebuild of the world’s first electronic computer Colossus pictured and the Harwell Dekatron or WITCH, the world’s oldest working digital computer.
It has also opened a series of galleries that trace the development of computing from the pioneering work of the 1940s.
Mr Crotty, chairman of software development company InsightSoftware.com, is also a trustee of TNMOC. He said: “To help the development of a museum such as this is an exceptional opportunity that comes once in a lifetime. I have watched this organisation grow and make astonishing achievements with very limited funding.
"My decision to donate has also been motivated by the increasing public awareness of the significance of digital heritage and the role and understanding it can play in inspiring current and future generations to become engineers and computer scientists."
TNMOC opened at Bletchley Park four years ago.
Trustees chairman Tim Reynolds said: “Already the Museum is recognised as one of the top computing museums in the world, but we have only just started.
"This new funding – the largest single private donation to any organisation on Bletchley Park – will enable us to unleash amazing potential.”
