The Role Of The Monitor; General - IBM 1130 User Manual

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THE ROLE OF THE MONITOR
General
The 1130 Monitor system has an outstanding feature,
lmown as the "system overlay scheme", designed to
assist you in fitting your programs into core storage.
This scheme is covered in some detail in Section
65, under "SOCALs".
Recapping that section briefly, the Core Load
Builder, which is given the task of building a core
load, or ready-to-execute package, also is given
the task of resolving the problem of more program
than core storage (if this problem arises).
Typically, many blocks of programming are
competing: for core storage: your programs, your
subprograms, the IBM subprograms, and the
Monitor control package itself. All must be in
core storage when required.
As a first step, the CLB attempts to fit the en-
tire package into core storage simultaneously. If
that does not fit, the CLB splits the IBM subpro-
grams into four groups:
Group 0 Basic
Overlay 1 Arithmetic (add, subtract, multiply,
etc. )
Overlay 2 Non-disk Input/Oltput (cards,
printer, etc.)
Overlay 3 Disk Input/Output
As step 2, the CLB determines whether the
package will fit in core if Overlay 1 and Overlay 2
share the same area in core storage (the SOCAL
area). The SOCAL area must be large enough to
contain Overlay 3 plus the larger of Overlays 1 and
2.
If this does not provide enough room, step 3 is
taken. Here, all three overlays (1, 2, and 3) will
share the same area, which must now be as large.
as the largest overlay.
Step 4, taken if step 3 does not work, consists
of a message informing you that this program is
too large to fit in core storage.
To illustrate this graphically, Figure 90.1 shows
the layout of the SOCALs required by a "typical"
commercial job. This "typical" program:
• Is written in FORTRAN.
• Adds, subtracts, multiplies, and divides.
• Uses the 1132 Printer, the 1442 Card Read
Punch, and the console typewriter (but not the
keyboard).
• Contains at least one PAUSE, STOP, and
CALL DATSW statement.
• Contains disk READ, WRITE, and FIND
statements.
If you punch an L in column 14 of the / / XEQ
card, the CLB will print a core storage map of
your program and all its subprograms, indicating
which are SOCAL or LOCAL, and what overlay
level is in effect.