[cromulent]

> Unfortunately, news of the 1582 promulgation had not yet reached the developers of Lotus 1-2-3, so they assumed that 1900 (being a multiple of 4) was a leap year.

Joel Spolsky mentions a more charitable take on this from Ed Fries:

> 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.

https://www.joelonsoftware.com/2006/06/16/my-first-billg-rev...

[staplung]

But that means Lotus 1-2-3 will be wrong again in 2100! We need to start a giant initiative to make sure everyone's Lotus 1-2-3 spreadsheets are Y2K1C compliant. Maybe by then, we'll be able to afford more than 640K of memory.

[bunabhucan]

Am I remembering it wrong or did Microsoft use an undocumented call in excel to grant it more memory than was possible for early competitors who didn't also write the OS?

[fragmede]

they did. later during the Netscape antitrust case it was shown in court that Microsoft gave Internet Explorer internal Windows hooks that Netscape couldn't have known about because they weren't documented.