Backwards compatibility. My Windows 8 Pro is 19.2 GiB (on disk). Of which 9.67 GiB is WinSxS. Which is essentially a giant component library containing dozens

Backwards compatibility. My Windows 8 Pro is 19.2 GiB (on disk). Of which 9.67 GiB is WinSxS. Which is essentially a giant component library containing dozens of different versions of DLLs third party programs use. 1.67 GiB is the driver store. 1.36 GiB is the 32 bit sub-system (SysWoW64). 700 MiB is the .Net framework (versions 1 through 4). So now we're down to 5.94 GiB of "stuff" which we can call the "OS" if you'd like, without any compatibility bits. Linux is so tiny because Linux has a terrible backwards compatibility record. Fortunately this is hard to spot because the distro's do such a great job of hiding it (and automate much of that via their respective package managers). But if Linux DID care about backwards compatibility at every level then the OS would be huge too, since you'd need tons of old libraries built in, tons of drivers for redundant hardware, and gunk like that.