I don't think "everything is a file" was ever supposed to mean "everything works just like a disk file", or even "everything has a name in the filesystem". It

I don't think "everything is a file" was ever supposed to mean "everything works just like a disk file", or even "everything has a name in the filesystem". It really meant "every kernel-managed resource is accessed through a file descriptor". Of course, even this formulation isn't always true (network interfaces and processes are the classic exceptions), but it's a true in a lot more cases. In this sense, "file descriptors" are really just the UNIX name for what Windows calls a "handle". This is still quite a good paradigm to follow - the semantics for waiting on, duplicating, closing and sending file descriptors to other processes are generally well-defined and well understood. For example, Linux exposes resources like timers, signals and namespaces through file descriptors.