🚀 go-pugleaf

On Wed, 23 Sep 1992 15:11:11 GMT Stephen Spencer said:
>Sorry if this is a silly question, but is there a good source for system
>calls on an IBM370?  We've been using the ASSIST macros, but I am also
>interested in knowing what the actual methods are (ie: how do I *really*
>output to the screen or get a character :)
>
"System Calls" generally refer to macro interfaces to the Operating System.
That is, an application program uses a "system call" to request a service
from the Operating System, such as 'write a record to disk' or 'read a
block from the console'.  Most often, these "system calls" require a pointer
to a control block, often called the parameter list in older systems.  Most
often, the actual interface to the hardware is reserved by the Operating
System for its own use and you, the application, cannot see or control it.

In some sense, your question is ambiguous.  Do you mean that you want
documentation for the "real" Macros used to generate the control blocks
and "system calls" rather than the ASSIST replacements; or do you mean
'How does the Operating System perform the actual processes that I have
requested via my system calls?'  The former is Operating System dependent
and differs between CMS, MVS, VSE, OS/2, etc.  The second is hardware
dependent, probably not available to you unless you are a systems programmer
(which you don't sound like), and requires a Component Description for the
particular device of interest (at least for mainframe devices such as 3380
or 3390 disk drives or 3270-like consoles.)

Or do you mean something else, like, "How does Operating System manage to
keep track of what it is doing for my program (or virtual machine) as
opposed to anyone else?  Or is it all of the above (in which case you need
about ten-to-twenty years experience and an acceptance that programming at
this level is a dying and underpaid art!)

Dwight McCann : "Big signature blocks are very inconsiderate!"