>I am still missing a big piece in my understanding.  Can anyone point to a
>good resource that can explain the difference between multi-processing and
>multi-threading?

Well, the Java VM and language offers multi-threading. The current Java/iX
implementation uses the green-thread model, where a single process switches
between the different threads of execution "on top of the OS". This means
that the application can handle multiple "tasks" at the same time, e.g. one
thread for each current http client connection. The next Java VM for MPE/iX
will be HotSpot (as far as I understand) and use Posix Threads. This will
result in a setup similar to separate processes, where each can be executed
by a different CPU. Green threads, a single process, won't benefit from a
multi-CPU machine, whereas Posix Threads will.

However, even with the current green threads implementation in Java/iX, you
could still have each thread create an "associated" child process (via fork
or CREATEPROCESS) to do "hard work" like direct Image transactions in COBOL
or Transact or Pascal or ... and thus gain better scaling on multi-processor
systems. This approach might even be better than the Posix Thread approach
in some cases, because not all of the MPE subsystems might be thread-safe.

You can probably find some multi-threading/multi-processing info in the DCE
documentation, as this is currently the only thread library for MPE/iX that
I am aware of. However, at HP World, you might visit Bill Cadier's talk on
the upcoming Posix Threads to get quite some add'l insight.

(PS... One reason why I like Java and Java Servlets is that it does provide
infrastructure for handling a thread pool... you simply declare your servlet
as "implements SingleThreadModel" and the servlet engine will maintain a pool
of objects in such a way that none is executed by more than one thread at a
time... By letting each object open a JDBC connection to a database, you can
have database connection pooling with minimum programming effort, too).