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Basic Disk Operating System (BDOS) Functions
4-34
There is a hierarchical ownership of these regions. The program in A controls all
memory from A through D. The program in B also controls regions B through D.
The program in A can release regions B through D, if required, and reload yet
another program. (DDT-86, for example, operates in this manner by executing
function 57, the Free Memory call, to release the memory used by the current
program before loading another test program.) Further, the program in Bean
release regions C and D if required by the application. However, if either A or B
terminates by a System Reset (BDOS function 0 with DL
=
OOH), then all four
regions A through D are released.
A transient program may release a portion of a region, allowing the released portion
to be assigned on the next allocation request. The released portion must, however,
be at the beginning or end of the region. Suppose, for example, the program in
region B in the previous example receives 800H paragraphs at paragraph location
100H following its first allocation request, as shown in Figure 4-2.
Length
=
8000H
!-IOOOH:
Figure 4-2 Example Memory Region
Region C
Suppose further that region D is then allocated. The last 200H paragraphs in region
C can be returned without affecting region D by releasing the 200H paragraphs
beginning at paragraph base 700H, resulting in the memory arrangement shown in
Figure 4-3.
Length
=
6000H
Length
=
2000H
:----1000 H:
1 __
7000H:
Figure 4-3
Example Memory Regions
Region C
111111/11/1
1111111/1/1
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