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Section
Subsections
Page
65
10
I
50
01
Program or LINK Area
Unused
COMMON
Program area
lOCAL area
SOCAl area
Flipper
Basic area
Core Storage
This area will contain
1. Your mainline program
2. All of your subprograms that are not LOCAL
or SOCAL.
3. All of the IBM-supplied subprograms that are
not LOCAL, SOCAL, or subtype
O.
4. All data (variables and constants) used by the
mainline and/or its subprograms, not placed in
COMMON.
This forms the third area in core where overlays
may be employed; in this case one program package,
or LINK, will overlay another.
As in the case of LOCALs, this is not done auto-
matically; it must be planned and executed by you.
Suppose you have written a very large (10,000-
word) program, named BIG. When you try to ex-
ecute it, you are informed by the Monitor that
it
is
too big. Looking at the program, however, you see
that it can actually be thought of as four program s,
connected as shown
in
Figure
65.
3 .
If you split BIG into four programs and place the
CALL LINK statements in the proper places, the
four will run essentially the same as one large pro-
gram (although possibly a little slower). Each pro-
gram or LINK may have its own SOCALs, LOCALs,
variable data, subprograms, etc. However, if the
LINKs must communicate with each other through
core-resident data (rather than disk data), this data
must be placed in the COMMON area, with the
COMMON statement (see next subsection). During
execution of such a program, while the location and
contents of the SOCAL, LOCAL, and LINK areas
may be continually changing, the COMMON area
does not change.
It
stays
in
the same place and is
not involved in any overlay.
BIG1
CALL LINK (BIG2)
,
"
BIG2
CAll LINK (BIG3)
1r
BIG3
BIG4
If not
If
CALL EXIT
finished:
finished:
CALL LINK (BIG2)
CALL LINK (BIG4)
Figure 65.3. A program. "BIG". segmented into four links
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