[geeks] On the subject of mainframes...

[gsm at mendelson.com]

On Sat, May 28, 2011 at 08:27:18PM +0000, vintagecoder at aol.com wrote:

>MVS (and this is a name that applies generally to OS/360 up to the current
>day z/OS) has always been about getting work into and out of the system as
>fast and safely as possible.

Yes. 

> In the early days and for a long time after,
>that input came from decks of cards and open reel tapes. It wasn't an
>interactive system by any means and today looking back it's sometimes hard
>to understand how we got anything done back then, but we did and we had a
>lot of fun.

It depends. Later MVT systems had a Time Sharing Option. It allowed you
to work with typewriter terminals to edit files, submit jobs, look at
the results etc.

It was not user friendly by any means, but you could get work done without
punched cards, etc.

Around 1967 (the wikipedia had a good article) IBM produced virtual memory
hardware for the 360/65. They wrote a virtual machine operating system 
for it that allowed them to run multiple versions of the operating system
at the same time, the same way that VM systems work on modern PCs.

By around 1969-1970 this became the commercial product CP/67 on the 360/67.

VM did not have any real user interface beyond being able to attach and
detach devices, start, stop and debug operating systems and manage virtual
print and card files.

A single user operating system called CMS was developed. CMS/67 could run 
on a real computer and was reasonably user friendly compared to what was
available in those days.

IBM replaced the 360's with the 370's. The 370's were externally 360's with
all of the options and a new virtual memory system (slightly different than
the 360/67's).

IBM released three different operating systems for the 370s. The most obscure
was ACP which was a 370 implementation of the 360 Airline Control Program
operating system. The original ACP ran MVT as a virtual machine.

CP/67 ran MVT, CMS, DOS, ACP. I don't think it allowed second level virtual
storage to run VM underneath it. The other operating systems did not support
virtual storage, so it really did not matter in many cases.

VM/370 did support second level virtual storage. 

IBM came out OS/VS 1 (MFT with virtual storage), OS/VS 2 (MVT with virtual
storage) later called MVS, and VM/370. VM/370 would run on any System 370
processor with the vitrual memory hardware (some early ones did not have it).

VM/370's CMS only ran in a virtual machine.

IBM still was giving away it's operating systems. They had no competiton, 
so it did not matter. 

Three things happened that changed that.

1. IBM realised that they could sell operating system add-ons for real money.
2. Ahmdal started selling a 370 clone. It ran MVS and VM unlike the RCA 360
    clones which only ran RCA's operating system.
3. Display terminals became available. (IBM 3270).

The last free release of VM/370 is available, and so is MVS 3.8, the last free
release of the MVT/MVS line.

Around 1985 IBM came out with the XA (extended architecture) systems and 
none of the XA operating systems were ever free. 

The real problem that I see is that the best editor for TSO was a
product called SPF and it was never free. It eventually became available
for CMS, but the CMS extended editor (not free), xedit, was pretty good
too. Both do things that no modern editor does.

So you can go up to MVS 3.8 (which I recommend highly over MVT), and VM/370,
but you are kind of stuck. You will never get a decent editor for them.

I've written hundreds of thousands of lines of code using both xedit and
SPF, but would never want to write any with the old editors (which I have).
think of writing a program used SED or VI in line mode.

>MVT was a great OS but if you never used it you're going to want to commit
>a lot of time to getting something out of it. I'll compare getting a
>running MVT system with doing a minimal NetBSD install. Well, it's way
>harder but they've already done the sysgen for you. After that, all you have
>is a basis for building a system you really want. You have an assembler,
>a few languages, and ways to get work in and out of the system, but not a
>whole heck of a lot more than that. Now you have to start writing your
>tools and building what you want.

I don't know what's available,  but you can find if you look around free 
compilers for fortran IV, PL/I and cobol. Maybe even a RPG and some other
obscure languages. You only be able to find the old assmbler, but it should
be good enough. 

Back in the old days, I was able to crank out 300 lines a day of tested, 
commented BAL code using SPF and the old assembler under CMS.

You probably could write the same projects in few hundred lines of code these
days. 

I've often thought about setting up a 370 under Hercules and running
VM and MVS under it, but except as an experiment in systems programing, I
can't think of a better use for it. 

I'm sorry I can't be much more than a buzzkill, but I've been there, done that
and don't see any reason to go back. Although the world ran on them in those 
days, I don't see any thing that a modern person would be interested in.

Geoff.

-- 
Geoffrey S. Mendelson N3OWJ/4X1GM
It's amazing how many people have no clue what the word "contiguous" means. :-(