Newbie questions

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Newbie questions

andybianchi
I'm totally new to hercules, mainframes, MVS, etc so I have a few,
possibly very stupid questions (which I'm sure may be a case of RTFM
but it might be easier if someone on the group could point out which
M to RTF to save me a bit of time ;-)

Background:

I've worked/played with Linux/UNIX mainly as well as the obligatory
Windows and also had a brief taste of iSeries which, at the time got
me thinking that I should learn more about 'different' platforms.

Recently I've been trying to setup a product running on AIX which
talks to DB2 on zOS.  Thankfully someone else looked after the latter
part of this but it got me thinking again that learning something
about mainframes might just be handy!

So, my plan is to install hercules, install MVS 3.8 (I'm following
Jay Moseley's instructions at the moment - they seem really good,
mind you I wouldn't know if they weren't), have a play with that and
hopefully learn enough so that I can cope with, at least, basic
understanding of what the zOS guys are on about.

So, some daft questions:

1) In hardware/real terms, what I am playing with with Hercules and
MVS 3.8?  If I was sat in the same room as this machine what would I
see?  Tapes, disks?

2) Is MVS 3.8 the 'newest' OS that I could run for free (except
Linux)?  What age is MVS 3.8?

3) How can I related what I do under MVS 3.8 to zOS (1.4 I think I've
been 'using')?  What are the differences?  What are the similarities?

4) Obviously I'm not going to get zOS and DB2 running under Hercules
so I can't play with that environment.  However, is there anything I
could be learning on Hercules that would help me understand what is
going on with zOS?  Is JCL useful to learn/understand for modern zOS?

5) I found one doc comparing Linux to Mainframe, are there any other
good reads that might just explain the inner workings of a mainframe,
possibly relating these to UNIX/Linux?

I understand the internals of UNIX/Linux (well I hope I do) and I've
done things such as assembly language and looked at the inner
workings of machines and I generally build all of my knowledge of
more abstract components, e.g. Java programming, on the lower level
concepts, e.g. by looking at the source for the Java Virtual Machine
(written in C and some assembly).  

I've taken this approach since taking my Acorn Electon apart and
adding extra bits to it by soldering components onto the PCB and then
writing ROM images and such to hack around with the insides.

So from micro->PC->UNIX machine I think I have a good understanding
of how things are working inside.

As for mainframes, I'm missing that whole chunk of knowledge and all
I see at the moment are lots of confusing numbers and weird commands!

Any help would be greatly appreciated :)







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Re: Newbie questions

Alessandro Brezzi
Concerning some literature, MVS and z/OS is very well documented; just for
starting refer to
 http://publibz.boulder.ibm.com/zoslib/pdf/zosbasic.pdf
 Consider to do many tour in http://www.redbooks.ibm.com for a lot of
documentation "hands on"
For tech ref manual, see
http://www-1.ibm.com/servers/eserver/zseries/zos/bkserv/ 
 HTH
 Alessandro

 2005/5/25, andybianchi <[hidden email]>:

>
> I'm totally new to hercules, mainframes, MVS, etc so I have a few,
> possibly very stupid questions (which I'm sure may be a case of RTFM
> but it might be easier if someone on the group could point out which
> M to RTF to save me a bit of time ;-)
>
> Background:
>
> I've worked/played with Linux/UNIX mainly as well as the obligatory
> Windows and also had a brief taste of iSeries which, at the time got
> me thinking that I should learn more about 'different' platforms.
>
> Recently I've been trying to setup a product running on AIX which
> talks to DB2 on zOS. Thankfully someone else looked after the latter
> part of this but it got me thinking again that learning something
> about mainframes might just be handy!
>
> So, my plan is to install hercules, install MVS 3.8 (I'm following
> Jay Moseley's instructions at the moment - they seem really good,
> mind you I wouldn't know if they weren't), have a play with that and
> hopefully learn enough so that I can cope with, at least, basic
> understanding of what the zOS guys are on about.
>
> So, some daft questions:
>
> 1) In hardware/real terms, what I am playing with with Hercules and
> MVS 3.8? If I was sat in the same room as this machine what would I
> see? Tapes, disks?
>
> 2) Is MVS 3.8 the 'newest' OS that I could run for free (except
> Linux)? What age is MVS 3.8?
>
> 3) How can I related what I do under MVS 3.8 to zOS (1.4 I think I've
> been 'using')? What are the differences? What are the similarities?
>
> 4) Obviously I'm not going to get zOS and DB2 running under Hercules
> so I can't play with that environment. However, is there anything I
> could be learning on Hercules that would help me understand what is
> going on with zOS? Is JCL useful to learn/understand for modern zOS?
>
> 5) I found one doc comparing Linux to Mainframe, are there any other
> good reads that might just explain the inner workings of a mainframe,
> possibly relating these to UNIX/Linux?
>
> I understand the internals of UNIX/Linux (well I hope I do) and I've
> done things such as assembly language and looked at the inner
> workings of machines and I generally build all of my knowledge of
> more abstract components, e.g. Java programming, on the lower level
> concepts, e.g. by looking at the source for the Java Virtual Machine
> (written in C and some assembly).
>
> I've taken this approach since taking my Acorn Electon apart and
> adding extra bits to it by soldering components onto the PCB and then
> writing ROM images and such to hack around with the insides.
>
> So from micro->PC->UNIX machine I think I have a good understanding
> of how things are working inside.
>
> As for mainframes, I'm missing that whole chunk of knowledge and all
> I see at the moment are lots of confusing numbers and weird commands!
>
> Any help would be greatly appreciated :)
>
>
>
>
>
>
>
> Community email addresses:
> Post message: [hidden email]
> Subscribe: [hidden email]
> Unsubscribe: [hidden email]
> List owner: [hidden email]
>
> Files and archives at:
> http://groups.yahoo.com/group/hercules-390
>
> Get the latest version of Hercules from:
> http://www.conmicro.cx/hercules 
>
>
> ------------------------------
> *Yahoo! Groups Links*
>
>    - To visit your group on the web, go to:
>    http://groups.yahoo.com/group/hercules-390/
>    - To unsubscribe from this group, send an email to:
>    [hidden email]<[hidden email]?subject=Unsubscribe>
>    - Your use of Yahoo! Groups is subject to the Yahoo! Terms of
>    Service <http://docs.yahoo.com/info/terms/>.
>
>


--
Alessandro Brezzi


[Non-text portions of this message have been removed]



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Re: Newbie questions

kvshetye
In reply to this post by andybianchi
Hi,

> 1) In hardware/real terms, what I am playing with with Hercules and
> MVS 3.8?  If I was sat in the same room as this machine what would
I
> see?  Tapes, disks?
>
Hercules is an emulator which emulates s/370, s/390 and z
architecture.  Hercules has the capability to emulate many
peripherals of mainframe like DASDs(Disks), Tapes, Printers, Punch
Cards and Networking components.  All peripherals like DASDs, Card
readers and printers are emulated using disk files which are kept in
your OS' filesystem.  When you put hercules ON, you can assume that
you have your mainframe hardware ready to load any OS which runs on
mainframes.  You IPL (boot) your mainframe OS which is stored inside
the emulated DASD.

> 2) Is MVS 3.8 the 'newest' OS that I could run for free (except
> Linux)?  What age is MVS 3.8?
>

MVS 3.8 is quite older version.  After that IBM has introduced OS/390
and Z/OS.

> 3) How can I related what I do under MVS 3.8 to zOS (1.4 I think
I've
> been 'using')?  What are the differences?  What are the
similarities?
>

The MVS 3.8 available is just the operating system.  On which there
are few older MVT compilers are also available.  But CICS, ISPF etc
are missing from it.  JCLs working on MVS can be run on Z/Os without
modifications.  All the OS utilities which are available for MVS are
also available under Z/OS.  So if you know MVS 3.8, Z/OS will not be
a difficult thing for you to understand.  Basic design of the OS is
same in both.  Both has consoles to operate, The console commands
which work on MVS 3.8 should also work on consoles for Z/OS.  The
only problem with this MVS 3.8 is, missing CICS and ISPF, and of
course compilers are too old.

> 4) Obviously I'm not going to get zOS and DB2 running under
Hercules
> so I can't play with that environment.  However, is there anything
I
> could be learning on Hercules that would help me understand what is
> going on with zOS?  Is JCL useful to learn/understand for modern
zOS?

You can learn little system administration and handling OS utilities
like to format DASDs, Copy/Edit datasets, compile and run programs in
COBOL, RPG etc.





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Re: Newbie questions

Tony Harminc
In reply to this post by andybianchi
On 5/25/05, andybianchi <[hidden email]> wrote:

> I'm totally new to hercules, mainframes, MVS, etc so I have a few,
> possibly very stupid questions (which I'm sure may be a case of RTFM
> but it might be easier if someone on the group could point out which
> M to RTF to save me a bit of time ;-)

If you like bottom-up approaches, you should very definitely read the
Principles of Operation manual. There is one for each architecture
level that Hercules supports: the original S/370 (early 1970s followon
to S/360), the early 1980s 370/XA, the 1990s ESA, and the 2000s
z/Arch. These books are all available online - the later ones on IBM
sites, and the earlier ones at places like bitsavers.org . They are
for the most part very very well written, and very self-consistent and
complete, though in the later versions IBM started to drop complete
documentation for certain features.

> 1) In hardware/real terms, what I am playing with with Hercules and
> MVS 3.8?  If I was sat in the same room as this machine what would I
> see?  Tapes, disks?

MVS 3.8 typically ran on a machine like a 370/168, which would
comprise several quite large boxes for the CPU (water cooled), I/O
channels, and disk and tape drives, printers, card readers, etc. MVS
also ran on smaller air-cooled machines like the 370/158.  Some
pictures of these are at:
http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_2423PH3168.html
http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_coi107.html
http://www-03.ibm.com/ibm/history/exhibits/mainframe/mainframe_2423PH3158.html

In architectural terms, S/370 is roughly a 32-bit, virtual memory
system (but with 24-bit, byte-oriented addressing). XA extends this to
31-bit addressing in the same 32-bit framework, and has a reworked I/O
system. ESA adds the concept of multiple address spaces addressible at
the same time (i.e. n x 2GB available to each program), and z/Arch
supports 64-bit addressing. There is a lot of room for argument about
which of the many features introduced with each level are
"fundamental" or "significant", but IMHO the addressing is the core
element.

Hercules provides emulation of almost all this hardware, and it is
possible to attach certain real hardware (e.g. 9-track tape drives) to
a box running Hercules. But mostly the emulation is done using PC or
UNIX hardware, and the whole thing is contained in the box.

> 2) Is MVS 3.8 the 'newest' OS that I could run for free (except
> Linux)?  What age is MVS 3.8?

MVS 3.8 is the newest free OS of this flavour, but there are modern
OSs (notably Linux) that run on the latest z/Arch machines and can run
on Hercules. There are also IBM OSs of other lineage that run on the
same architecture, and the freely available versions of these may be
slightly newer than MVS 3.8. But around 1980 was when IBM turned all
its mainstream OSs into chargeable products, so there's not much
available later than that.

> 3) How can I related what I do under MVS 3.8 to zOS (1.4 I think I've
> been 'using')?  What are the differences?  What are the similarities?

There is a very large overlap both from the bottom-up architectural
view, and from the end-user view. Almost anything you learn on MVS 3.8
is applicable to the latest z/OS, and indeed the binary image of your
program last compiled in 1972 is likely to run fine on z/OS 1.4. Of
course there are many features in the newer systems that are not on
the old. And from the end-user point of view, although things in some
ways "work the same", what end-users actually *do* with z/OS is
typically much different from what they did with MVS 3.8. For example,
in the last days of 3.8, it was not uncommon for real punch cards to
still be in use to hold program source, whereas now a card reader is a
museum piece. On the other hand, the nature of disk files that hold
program source and executables now is pretty much the same as it was
in 3.8 days.

> 4) Obviously I'm not going to get zOS and DB2 running under Hercules
> so I can't play with that environment.  However, is there anything I
> could be learning on Hercules that would help me understand what is
> going on with zOS?  Is JCL useful to learn/understand for modern zOS?

JCL is still a lot the same, though it is doubtless used much less by end users.

> 5) I found one doc comparing Linux to Mainframe, are there any other
> good reads that might just explain the inner workings of a mainframe,
> possibly relating these to UNIX/Linux?

See the Principles of Operation books and some of the IBM Redbooks
(search the redbooks site for "Linux").

> I understand the internals of UNIX/Linux (well I hope I do) and I've
> done things such as assembly language and looked at the inner
> workings of machines and I generally build all of my knowledge of
> more abstract components, e.g. Java programming, on the lower level
> concepts, e.g. by looking at the source for the Java Virtual Machine
> (written in C and some assembly).

You could certainly look at the Linux/390 source to learn a bunch
about the z/Series hardware architecture, but this will teach you
little about the software architecture of MVS and z/OS. It all depends
on what you're interested in.

> Any help would be greatly appreciated :)

One more overview I can suggest is the paper Development of 360/370
Architecture: A Plain Man's View, by Jeff Gribbin at
http://pucc.princeton.edu/~melinda/ . It's old (1989), but still a
good introductory read.

Have fun...

Tony H.


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