I don’t understand how one could build just a kernel with the required graphical drivers with that few number of lines... But maybe at that time the requirements for each part of the system were orders of magnitude simpler (memory protection, scheduling, fault isolation, graphical functionalities,...).
http://xeroxalto.computerhistory.org/xerox_alto_file_system_...
I just noticed that site includes the code, apparently including the microcode, in addition to papers and reports! (I'm not sure if the microcode programs are included in Kay's 10 - 20,000 line estimate.)
i.e. "math wins"! ... when coupled into the design of the entire system.
And ... we would have loved to have had more microcode!
I'm still having a hard time understanding how having to ability to program your own "assembly" operation through microcodes could reduce the number of lines for huge programs that drastically. At worst you could still code those operations with the higher level language (smalltalk)... I can imagine how that would make things slower, but that's another issue.
Another thing i wonder as someone that hasn't coded in assembly since school : isn't the set of low level instructions required to build most regular programs pretty much settled now ? I'm not talking about high performance or 3D graphics, or AI. Only things personal computers have been doing for the last 30 years.
Put it differently: supposing intel gave use the possibility to reprogram a large set of its assembly instruction using microcodes, would the linux codebase be radically smaller ?
To respond to your technical questions about microcode. Microcode (and CISC architectures in general) are motivated by making the compiled binary programs as small as possible - each single machine instruction can do a lot because it runs a lot of microcode. The optimal set of machine instructions isn't settled once and for all, it depends on available technology. The Alto only had 128 kilobytes of RAM, so it was crucial to design an instruction set where compiled programs were as small as possible. So (I recall) their CPU used a stack rather than a lot of registers because then most operands could be implicit - that saves a couple of bytes in a typical instruction. Now that gigabyte memories are commonplace, the design trade-offs are quite different. But I think the microcoded instructions made the programs shorter at the source code level just because they made it unnecessary to re-implement the low level graphics operations (etc.) over and over in system and application code.
I believe Linux isn't built the same way the Smalltalk system was. One glaring difference is the use of C - with that you can't get very high level and are always programming at a very low level. You also force all integrations to be at a very low leve, given how the ABI and syscalls work.
You can do quite a bit more if you use a higher level language with very good meta programming, for instance Lisp or Smalltalk. E.g., you could imagine very high level abstractions that get translated to lower level logic automatically. Unfortunately, this is not an area that has been extensively adopted IMO, and the mainstream thinking is we need to use lower level languages for operating systems and such.
> supposing intel gave use the possibility to reprogram a large set of its assembly instruction using microcodes
Actually Alan Kay has been critical of Intel not doing this. It may not affect Linux much but it will definitely open the door for systems using more advanced techniques, specifically the ability to build high level emulators. See https://news.ycombinator.com/item?id=15282739 for more.