

OpenVMS vs. Unix - ddelony
http://www3.sympatico.ca/n.rieck/docs/vms_vs_unix.html

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bediger
Perhaps the most un-biased comparison I've ever seen. It even includes a bit
about different VMS filesystems, a neglected topic.

But I think this misses a lot of key points. You cannot compare operating
systems without comparing a few key points:

1\. What is a "process" (a.k.a "task", or "job") on this system? In
traditional Unix, a process was an address space, a thread of control (the
schedulable unit, another key comparison point), a signal mask, a (set of)
signal handler(s), a UID, and effective UID, a group ID, and a set of file
descriptors, and maybe some other stuff like priority. What's the equivalent
in VMS? Nobody ever charts that out.

2\. What's the lifecycle of a program? That's not the same as the lifecycle of
a process in VMS, if I understand correctly. Contrast and compare. Extra
points for complete explanation of starting a process (fork/exec vs
CREATE$PROCESS or whatever VMS has).

3\. What's the on-disk format of an executable file? How does the OS decide if
it can execute a file? How does the OS decide to interpret a file
(#!/usr/bin/env perl) or directly execute it?

4\. How does a process do I/O? Synchronous or asynch? Are different classes of
devices treated differently?

5\. Does a file have a "type"? What, precisely does the "type" mean? On-disk
format (fixed length records for example, or stream-of-bytes) or "a document's
owner"?

