The Windows Update Marathon in a VM: From Windows 1.01 to XP
The level of backwards compatibility in Microsoft products is very impressive.<p>Microsoft Office 2019 can open .doc files created in Microsoft Office 97 and upgrade them to a modern format, with zero loss (except for things like OLE objects, which are no longer supported for security reasons). My parent's computer has documents which haven't been touched in 20 years and they still open just fine.<p>Or applications written for Windows NT that still work - unmodified! - on Windows 10 thanks to layers of compatibility hacks. A true feat of engineering.<p>If you want to read more about the horrors of maintaining APIs that are backwards compatible with software written decades ago, I can heartily recommend Raymond Chen's blog: <a href="https://devblogs.microsoft.com/oldnewthing/" rel="nofollow">https://devblogs.microsoft.com/oldnewthing/</a>