The two-digit year was used in early software because computer data storage was very expensive.
Dates are the most common data elements exchanged between software programs.
While the problem is simple, fixing it is a complicated and enormous task. These estimates were originally thought to be high, but more recent experience indicates they actually may be on the low side. They determined that 4.4 million lines of code in more than 4,000 programs were affected. Purdue University began conversion in 1994. It appears that many universities are addressing the Y2K problem by wholesale replacement of existing systems, either as part of an existing technology upgrade plan or by accelerating and expanding their replacement plans.