.NET includes ngen, the Native Image Generator, it's run during the install process and compiles much of the MSIL bytecode into x86 assembly code ahead of time, however this process isn't done during the dotnet9x setup, and after setup appears to fail in an odd way.

When running ngen install "mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089" as the original setup would, it prints a lot of (expected) warnings to the console, compilation appears to complete? However installation to the assembly cache fails with E_INVALIDARG, this appears to happen for every assembly:

Examples on Windows 98 (where this should definitely work):

ngen, while not needed does drastically improve startup performance where available and would be especially helpful on older, slower machines running Windows 9x.