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65

Primordial Unix on the PDP-7 was in many ways very different from what we know today. Directories existed but were very awkward to use; in practice most work was done in a single directory. Most importantly, paths did not yet exist. What was implemented early on though was a simple syntax for IO redirection on the commandline. Whereas on Multics one ...


32

From this list of Multics features, almost all are recognizable in modern UNIX-style systems in one form or another. Looking for distinctions between is two is made difficult due to the longevity of UNIX and the proliferation of its children. For me, the most interesting distinction between Multics and UNIX (and most operating systems to follow) was Multics'...


23

There are a number of ways to use Multics today. One option is to run it locally under an emulator. The source code that's available should run (under emulation) on most Linux systems, Mac OS X, and Windows, even the RasPi. See the Multicians site for details (a cookbook is available). Another option is to telnet (or ssh) to a public access system. I don'...


14

In Multics, not only was all data mapped into memory, but all binary executables were what we now call DLLs. There was no natural "main program" concept: every binary executable was a compiled function. Processes were extremely "heavy": you got one when you logged in, and everything you ran was a DLL linked into that process. This messed ...


13

Yes. The dps8m emulator simulates the GE-645 machines well enough to run Multics. The open-sourced code has been successfully run under the emulator. There's even a getting started guide with some bugfixes, meant specifically to be run under the emulator.


9

A couple other significant differences between Multics and early Unix systems in the security area: Multics had rings (8 in commercial versions), whereas Unix only had two effective rings -- supervisor and user. This allowed privileged subsystems to be created that would run in process, but be protected from tampering by user (ring) manipulation. This was ...


8

Another significant difference between Multics and Unix was the size of the virtual memory accessible to a process. It is true that each Multics segment was limited to 255K 36-bit words in length. But each process mapped more than 300 such segments into its address space. About 1/2 of these segments belonged to kernel and inner-ring programming ...


7

All these answers accurately describe the most salient features of Multics. One of the main consequences was that it could only run on specialized hardware. From a programmer's standpoint, dynamic links had a fantastic use: when debugging a program, you could pause on a breakpoint, fix your code, recompile it, update the link and continue execution (if you ...


5

Perhaps the best way of thinking about it is that Unix basically is a minimal implementation of Multics (the ideas in it a least) with absolutely everything that was not strictly necessary to bring up the system stripped out. So segmenting and virtual memory are not really needed (at least to get started). Complex permissions, ACLs or protection rings, ...


3

There were other hierarchical file systems around. The Burroughs operating systems used (and as Unisys, still do) / Although in a someone clunky way: (PHYS212)ACOUSTICS/RAYS/OUTPUT ON USERPACK ^^^^ usercode ^^^^^^^ device MS-DOS and Windows also accept / in file paths, in addition to \. It is the command language where this does not ...


2

DTSS, developed around the same time as Multics, and influenced by it, used : as the directory separator. A leading : was used for absolute paths (starting at the root directory). There was no easy way to indicate "parent directory" (Unix/Linux ..) — programs that needed to walk the directory tree had to keep track of things themselves.


1

Not an answer, really, but I would suppose that the name would have been seen as natural for Project MAC's goals. The name MAC, in one of its many interpretations, stood for "Multiple Access Computer". Computing as a utility, that is as a service, had been talked about at MIT from the beginning. John McCarthy used the term at least as early as 1961....


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