From: tspencer@pilot.njin.net (Thomas Spencer IV)
Newsgroups: alt.folklore.computers
Subject: Re: IBMs true monsters?
Date: 26 Dec 92 03:21:22 GMT
Organization: Rutgers Univ., New Brunswick, N.J.


d40937@boole (Jean Yves Desbiens)  wrote:

>Do any of you know anything about IBM's very big mainframes,
>at our school they upgraded one they had for about 15 years and
>it cost millions to do it. I think the model of the computer is 3090
>( please correct me ) and it runs the MVS operating system that can
>create virtual machines

   It is VM that creates the Virtual Machines.  You can then run
another OS in each of the virtual machines, either another VM, or a
CMS session, or even AIX/370 (Non-native Unix for 360 and 370 arch. 
machines.  DOS/360, DOS/VSE, etc, etc, including MVS are popular
"client" OSs that run in VM's virtual machines.  

<Lots of stuff deleted, but commented on anyway>

      IBM's large systems were designed to do transaction processing,
and the standard they use is CICS.  The system was never designed to
be "friendly" to the casual user, but stable for the MIS department.
That means the system needs to have the staff that has grown up around
them, otherwise they "break" very quickly.  To illustrate this, I'll
offer the example of the school I work for.  In the different classes
that use the mainframe for lab work, an operator needs to be on hand
to help the students.  This is because the way the OS is set up, a job
can easily get stuck at a point, and wedge up the other people.  The 
operator has to clear the job because once it has been submitted, the
user looses control of it.  If his job gets stuck, all of the 
other people's work will sit in the reader queue until hell freezes over.
The operator has to unwedge the system.  Another problem with IBM's 
systems is the requirement of JCL.  It is a latent holdover from the
time that programmers were cheap and the hardware expensive.  Now that
the $/mip/sec is so low, it is a bothersome hassle.  Improvements have
been made, but not really.  To illustrate how important the JCL is,
try inserting a Include line that includes itself.  Submit multiple times.
On our 4381, they end up having to re-IPL the entire system.  It is
a trivial way to bring the system down.
      The systems themselves have to be very fast, because of the 
system software it runs.  The requirement of implementing virtual copies
of itself is not all that difficult, and doesn't cause the hardware
much trouble.  It is the software that has the difficulties.  IBM pioneered
the idea of "backward" compatiblity, as well as upward compatiblity.  
Supposedly, the software written for the orignal 360's should run with
minor modifications on a brand new ES9000.  This has caused two major
phenomenon.  First, it has created great amounts of customer goodwill, and 
customer loyalty for IBM.  That is the good part (for IBM, not for the rest
of us, I hate IBM and the systems, I'm the PC and UNIX admin for the college).
The bad part is that IBM has had to make fewer improvements over time because
they had to make sure they broke only parts of a customers application
with each update.  Since all of the installed apps were mostly custom designed
to begin with, any problem caused by a new update "breaking" the app resulted
in the local MIS department having to modify the program.  Over time, the
constantly patched program became more and more difficult to maintain, so
IBM could change fewer and fewer parts.  Stagnation in development.  They
could add new features, but the old parts all had to remain, no matter how
much they slowed the system down.

Tom Spencer