Post by Jeroen Baten ***@jeroenbaten.nl [hercules-390]I wrote 8 books about Linux, so I guess I know my way around that
system. :-)
Seems likely... Do you specialize in one area, or try to cover everything?
You are not, for instance, a kernel specialist or one in end-user
interfaces?
Post by Jeroen Baten ***@jeroenbaten.nl [hercules-390]And I am just curious to learn more about the ways a mainframe works.
There are several OS options but since I know neither maybe mvs is just
as good as any?
I'm still not clear on your goals. "The mainframe" is just another hardware
platform that, as I'm sure you know, can run a number of operating systems
including Linux. Since you already know about all there is to know about
Linux, do you want to learn about the other OSs that appeared for various
reasons to run on the IBM hardware, or are you interested in the actual
hardware architecture, or...?
The hardware is very interesting in its own right, and was the first
"hardware family" or if you like "system architecture" in that the
Principles of Operation describes a core set of features that all models
implement, and optional features that may be found on a given model. A few
models also implemented unique or extended features beyond even the
core+optional, but these were relatively rare.
The core has evolved over time, of course, under different names from S/360
in 1964 with around 100 intructions to S/370 base (not much different) to
S/370 virtual storage, to S/370 XA in the 1980s to ESA/370 to zArch
(64-bit) which now has well over 1000 instructions. But to this day an
application program last compiled in 1964 is likely to be able to run on
todays latest zArch machine, which speaks not only to hardware
compatibility but to that of at least some of the OSs.
MVS (now z/OS) is probably the most well known IBM OS for these
architectures, but perhaps not the most common. Certainly in the 1980s
there were many more VM/370 licences than there were MVS/370. These days no
one but IBM knows how many copies of any of their OSs are extant and on
what hardware, but educated guesses suggest well under ten thousand, and it
may well be much lower than that. On the other hand, a significant portion
of the world's corporate data processing is still performed on these
systems.
The architecture was historically very programmer friendly, but times have
changed and the newer versions are harder to write well performing
assembler code for. As on most current platforms, optimizing compilers
rule. So for these and other reasons (notably the non availability of IBM's
current OSs for hobbyist use), it does make sense to learn at least
initially about the older architecture versions and their OSs.
In some ways you will find programming for these OSs much the same as for
any other; in other ways you will very much be a stranger in a strange
land. It's important not to dismiss these older systems as something run by
nerdy men in white lab coats with boxes of punched cards, or to discover
that something works very much differently from what you are used to, and
give up because it's so weird.
You will find lots of knowledgable people here, with varying opinions. Ask
whatever you want and you are pretty sure to get at least one answer, and
maybe three incompatible ones.
Welcome.
Tony H.