unix & real time -- is a rewritten UNIX still UNIX?

[idallen at watmath.UUCP]

> From: gwyn at brl-tgr.ARPA (Doug Gwyn <gwyn>)
> 
> [That UNIX does not do real-time stuff well] is an old myth based partly
> on fact.
> 
> [List of drawbacks was here.]
> 
> All these drawbacks can be overcome by a competent UNIX system programmer.

But is what you get after all those hacks still UNIX?  Someone posted
a simple "fix" to a "bug" in Berkeley Pascal involving a missing
"default" in the CASE statement, and the cries went up that the
resulting language was no longer "Pascal".  Interesting point.  

How much UNIX can you hack up and still call it UNIX?   An interesting
question, but not the central point I want to make.

UNIX can do anything if you just rewrite this or that.  The same
applies to any piece of software -- if you rewrite it, it can do
anything.  I guess people who pose questions about what UNIX can do
have to be more explicit when they ask.  For example (hypothetical): I
have a binary multi-user UNIX 4.2bsd.  Can *my* UNIX do real time stuff
nicely?  (Answer: No.)  I now have an old V6 UNIX with source code.  Can
*my* UNIX support virtual memory? (Answer:  Yes.  Just have a competent
UNIX system programmer overcome this drawback by modifying the kernel.)

When one says X supports Y after {one,six,twenty} man-months of
rewriting, is that a fair answer?  I think not.  I think a fair answer
would say "No, X doesn't support Y, but if you want to spend N weeks
changing X, *you* can create *your own* version of X that supports Y."
-- 
        -IAN!  (Ian! D. Allen)      University of Waterloo