When was the decision made to store years in computers as a 2 digit code?

Back in the 1960s and 1970s. Computer space was much more expensive back then. Today we can store huge amounts of data on small devices using microprocessors, but in those days they had to use vacuum tubes. Computers filled whole rooms and still only held a fraction of the data you can store on your iPod. Two-digit years ("69" for 1969, for example) were used to save space and money.