Recreating the lost SDK for a 42-year-old operating system: VisiCorp Visi On

My partner Elaine Gord was on VisiOn's C compiler team in 1982-1984 with two others. They experimented with having two instruction sets: the native 8088 code for best performance, and a C virtual machine bytecode for code density. The two modes were mixed at the function level, and shared the same call/return stack mechanism. This was terrible for speed, but was thought necessary because the target machines did not have enough ram for the total VisiOn functionality. I don't know if the bytecode scheme got into "production".

All of Microsoft's applications used to do that! The 16-bit versions of Word, Excel, PowerPoint, etc all were implemented using bytecode. That technology was only integrated in Microsoft C and made public in 1992 [1], before that the Microsoft applications group used their own private C toolchain. A copy of it can be found in the Word 1.1 source release [2] ("csl").

[1] https://sandsprite.com/vb-reversing/files/Microsoft%20P-Code... [2] https://github.com/danielcosta/MSWORD