Why there is a 1904 Date System options in excel?

"Yeah, but probably an intentional one. Lotus had to fit in 640K. That's not a lot of memory. If you ignore 1900, you can figure out if a given year is a leap year just by looking to see if the rightmost two bits are zero. That's really fast and easy. The Lotus guys probably figured it didn't matter to be wrong for those two months way in the past. It looks like the Basic guys wanted to be anal about those two months, so they moved the epoch one day back."

"Aargh!" I said, and went off to study why there was a checkbox in the options dialog called 1904 Date System.

출처:

Joel on Software - My First BillG Reveiw

P.S:

빌게이츠가 모든 스펙을 다읽고 이를 이해했다는 내용이 참.. 감명깊게 느껴지네요 ㅎㅎ