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"Mainframes now run what is called z/OS; most recently it was
called OS/390, and before that it was called MVS (multiple
virtual storage)."
Gary,
It gives you some idea of when I last worked on an IBM
mainframe, somewhere about the time I switched to a
workstation specialist. I cannot claim to have invented system
programming, but I can lay claim one of the earliest
recognizers of the need. At the time it was a difficult sell.
Out of the gate I was only partially successful: the customer,
Ducommun Metals, allowed the candidate, Jack Whitfield, to
do it as long as it didn't interfere with his regular programming
duties.
All of this arose from the DD statement in the JCL. The fact
that we moved blocksize and buffer number, two variables
which most effect performance, from the application level to
the system level created a need for someone responsible for
managing system resources.
Before that time programming had two general categories of
programmers: application programmers and "utility"
programmers. This later wrote the "glue" applications like
sorts and other such utilities which crossed application
boundaries. These utility programmers quickly filled the
ranks of system programming.
In my experience the difference between IBM and its
mainframe competitors lay in its confidence in the intelligence
of its customers. They had to use that intelligence in the
ongoing tuning of the system resources of the operating
system. IBM's competitors offered a package deal: pick a size
and it determined the fit. Thus IBM's software, its operating
system, its database managers, its utility programs (among
them the sort utility) placed demands on customer personnel
not required by others.
The ultimate benefit of such demands upon skilled personnel
lay in increased throughput, i.e. lower per transaction cost.
Also it didn't hurt when it came to competitive benchmark
faceoffs in marketing the products...whether it was MVS, IMS,
or CICS. I particularly enjoyed the advantage I had with IMS
and CICS when going up against homegrown database and
transaction processing systems.
I sometimes could hardly restrain my joy when some
unsuspecting KIA told his manager not to pay IBM such
outrageous prices for software as he could provide it for much
less. In those instances I used to suggest on a public forum of
the department to insure that he no longer interferred in such
major decisions.
However, I digress. Peter asked about OCL whose role in UNIX
parallels that of JCL in OS/360 and its descendants. While
they have similar roles they certainly differed in their
functional offerings related to performance tuning. You can
do it in MVS or z/OS. You can't do it in UNIX...unless, of course,
you run it under z/OS.
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