My understanding from other anecdotes about Microsoft is that a lot of their internal tooling, for a very long time, remained the kind of hideous nightmare of interwoven dependencies and build times measured in hours that we try to avoid in most modern setups.

I would speculate that in most parts of the company that haven't been left to rot that's hopefully no longer true, but I have no direct anecdotes about that, I just would have assumed it to be a target for someone looking for their iteration cycles to be saner at some point, and once one group managed it, etc.

never was part of Windows, but from my limited interactions with it the old build system was a chimera of Perl scripts, passes, Makefile-like things and other tooling. build labs would run and jobs would take hours.

it underwent a Herculean effort to modernize it, converging on the actual VS build system and from sd to git. it seemed much healthier last I looked.