System/380 Overview

The VM/370 SixPack runs on the Hercules mainframe emulator.  It can also run on
the Hercules/380 emulator produced by Paul Edwards.  Hercules/380 extends the
System/370 architecture by adding support for 31-bit addressing and the BASM
instruction. You can download Hercules/380 from

http://downloads.sourceforge.net/sourceforge/mvs380/hercules380-3_07-1_0.zip

When the VM/370 SixPack is running on Hercules/380, the initial logo screen
will display "VM/380" at the top.

What does this mean?  Remember that VM/370 knows nothing about 31-bit
addressing.  Therefore if you run the VM/370 SixPack on Hercules/380 with
archmode set to S380 in the configuration file, Hercules will supply an
emulated computer with more memory than VM will ever address.  However, you can
access this memory from a CMS program.

There are two ways to access this memory:

1.  From a C program you can use malloc() to allocate a large (dozens of
    megabytes) chunk of memory.  If there is not room for memory from CMS it
    will be allocated from memory above the 16MB line.

2.  From an assembler language program you can use the GETMAIN macro with the
    LOC=ANY keyword to allocate memory from above the 16MB line.  Be sure that
    OSMACRO MACLIB is in the GLOBAL MACLIB list.

There are two important restrictions in using this support:

1.  Note that you can only do this from one CMS user at a time:  there is no
    protection from multiple users accessing this memory.

2.  You cannot use memory above the 16MB line as a buffer for any sort of I/O
    subroutine calls or instructions.