What is the 12KB icon file 'moricons.dll' that won't delete from Windows?

'moricons.dll' is a file that literally contains many icons (more icons), and remains in Windows 11. It is only 12KB in size and stores compact icons from the Windows 3.1 era, which are different from today's complex icons. Raymond Chen, a Microsoft developer and self-proclaimed Windows encyclopedia, explains that moricons.dll is 'a file that symbolizes Windows' thinking on compatibility.'

What were the intended uses of those icons in moricons.dll? - The Old New Thing

https://devblogs.microsoft.com/oldnewthing/20250505-00/?p=111143

Windows 3.0, released in 1990, was the first to allow users to run MS-DOS programs in a window, but it had a simple icon that just said 'DOS.' Windows 3.1 brought an improved GUI with different icons for each application.

Originally, these icons were stored in the Program Manager (progman.exe), but as their number grew they needed their own storage - this storage was moricons.dll, the file that still contains the icons for popular applications from the early 90s, including Turbo Pascal , Quattro Pro , WordPerfect , Lotus 1-2-3 , cc:Mail , and many more.

According to Chen, the moricons.dll icon used in Windows 3.1 was converted to a shortcut file in Windows 95 and has been passed down in subsequent versions. This compatibility chain was theoretically broken during the transition from 32-bit to 64-bit Windows because 64-bit Windows does not support MS-DOS programs.

by biggraham

However, since the focus of the 64-bit transition was on compatibility with the new system, reviewing the old code was not really a priority, and moricons.dll was left in place because it was only 12KB, posed no security risk, and there was a chance that someone was still using the old icons.

So, moricons.dll has been carried over to Windows 11 because it was decided that it was better to tolerate the small problem of 12KB of storage usage than to risk potential compatibility issues.

'It's better to let sleeping dogs take up 12KB,' Chen said, suggesting that sometimes leaving legacy code alone can be the safest option.