Scarily, I have single, hand-written source files that would barely fit onto a 3.5" disk.
Since that was downvoted for some reason, here's the source file I was thinking about. It's 762K, so about half of a 1.44 MB 3.5" disk. The total for the whole directory (itself a fraction of libvirt) is 9.2 MB.
Suppose you change one line, how long does it take to recompile that file?
That single file takes 0.56 seconds to compile on my i7 laptop. However deleting and recompiling that file triggers a relink of the library, and then a relink of all the utilities using the library, and that takes a bit longer.
Technically, that file wouldn't fit on the 3.5" disks I used in college (400K Mac and 720K PC).