Daniel Kosack writes:
> >        Interestingly, I have heard that Linux (a free Unix)
> >        is very stable.
>
>         Not a chance.  Linux is decent for starting out, but experience
> has taught me not to risk my neck on it anymore.
 
This is interesting. I have found it extremely stable; all my unplanned
shutdowns have been caused by hardware problems -- which has not been the case
with our NT system. What versions of Linux did you run, and what kinds of
applications? I'm using 1.2.13; it's being used for software development,
routing, and Internet services (mail, ftp, www). I also run X clients on it,
though not an X server.
 
> FreeBSD seems to be
> much better, and actually complies to a standard, BSD 4.4.
 
Linux versions after 1.2.1 comply with applicable Posix standards.
 
>
> >    (2) Uses more resources -  memory and CPU.
> >        I know most Unix programs tend to have
> >        character-by-character interfaces or GUI
> >        interfaces while MPE programs tend to
> >        be block-mode or line-mode.  Are there
> >        other reasons why Unix uses more system
> >        resources?
>
>         System resource utilization depends on the architecture and
> design of the OS.  DEC Alpha and OSF/1 are horrible and bloated when it
> comes to memory usage.
 
In my admittedly limited experience, Unix performace problems are more related
to applications. This is a bigger problem than on MPE, since Unix provides
very few application services of its own, meaning that application designers
must supply more of the necessary scaffolding. A Unix DBMS must either live on
top of Unix services or replace them entirely; MPE's IMAGE and KSAM are
tightly integrated with the operating system and can take advantage of
lower-level services that would otherwise be hidden from application-level
programs.
 
It's also been my experience that Unix has so many services that are "good
enough" without being _really_ good, that developers have tended to rely on
them rather than thinking up better ways to do things. When the development
applications are scaled up, the limitations of the services become apparent.
One old example of this is the file system: it's optimized for access to
fairly small files, but it's VERY good with them. So developers rely on
sequential access to small files, but this doesn't scale well to large
applications. (Unix file systems are improving in this regard, so this
statement is no longer true of many commercial implementations.)
 
Another example is that process launching under Unix is quite fast. Not
blinding, but quite fast. So developers rely on launching a lot of processes.
But again, this doesn't scale well.
 
This is also the reason that porting to MPE isn't very easy despite MPE's
decent and improving POSIX compliance: the techniques for optimimum
application performance are quite different. For an illustration of this, look
at the performance difference between httpd and HP's OpenMarket WWW server.
These two programs perform the same functions, but HP's implementation,
optimized to take advantage of things MPE does well (and avoid the ones it
does poorly) runs several times faster.
 
-- Bruce
 
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