Re: [TUHS] Early non-Unix filesystems?

Warren Toomey scripsit: Not only that, but a non-tree-structured directory system: the directories themselves were a general directed graph, and it was possible to have any number of arbitrary hard links to a directory. This was simplified in later Unices to the tree-structured directory system we have today, where the only hard links to a directory are the named link from the parent, the "." link from self, and the ".." links from the child directories. There was also no concept of pathnames in PDP-7 Unix, neither relative nor absolute. The link syscall was link("foo", "bar", "baz"), meaning to cause entry "baz" in directory "bar" in the working directory to be the same file or directory as entry "foo" in the working directory. So for example, each home directory had a hard link to the main binaries directory, conventionally named "bin", and the shell could not execute commands out of a directory that did not contain a "bin" link. With no reliable ".." entry, there was also no way to recover from a chdir, and traversal had to be done as digraph traversal rather than tree traversal. In particular, incautious use of unlink could cause the directory graph to become partitioned, requiring low-level disk surgery to recover. An interesting property of the ODS-1 (RSX) file system was that the root directory contained the i-node table as a file named INDEXF.SYS. This allowed ordinary programs to inspect the i-node table without messing about with raw disks. It also contained a self-entry named 000000.DIR, but other directories did not contain self-links. -- John Cowan http://www.ccil.org/~cowan cowan(a)ccil.org The internet is a web of tiny tyrannies giving an illusion of anarchy. --David Rush