1. Saeed is writing a really nice series of articles starting here: https://www.visualstudio.com/learn/git-at-scale/ In the first one, he lays out how we think about small/medium/large repos. Summary: size at tip, size of history, file count at tip, number of refs, and number of developers.

2. Fairly confident, at least as far as usable repos go. Given how unusable the Windows repo is without GVFS and the other things we've built, it seems pretty unlikely anyone's out there using a bigger one. If you know of something bigger, we'd love to hear about it and learn how they solved the same problems!

3. Windows is a 30 year old codebase. There's a lot of stuff in there supporting a lot of scenarios.

Is it possible to checkout (if not build) something like Windows 3.11 or NT 4?

As far as I can recall, this is not possible using Windows source control, as its history only goes back to the lifecycle of Windows XP (when the source control tool prior to GVFS was adopted).

Microsoft does have an internal Source Code Archive, which does the moral equivalent of storing source code and binary artifacts for released software in a underground bunker. I used to have a bit of fun searching the NT 3.5 sources as taken from the Source Code Archive...

I recently heard a story that someone tried to push a 1TB repo to our university Gitlab which then ran out of disk space. Sure, that might have been not be a usable repo but only an experiment. Still, I would bet against the claim that 300GB is the largest one.

300 GB is not the size of _the repository_. It's the size of the code base - the checked out tree of source, tests, build tools, etc - without history.

It's certainly possible that somebody created a 1 TB source tree in Git, but what we've never heard of is somebody actually _using_ such a source tree, with 4000 or more developers, for their daily work in producing a product.

I say this with some certainty because if somebody had succeeded, they would have needed to make similar changes to Git to be successful, though of course they could have kept such changes secret.

1 TB of code?

I'd sure like to run that as my operating system, browser, virtual assistant, car automation system, and overall do-everything-for-me system...