QBX.EXE 7.10 Expanded Memory Usage Better Than 7.00; 32K Table (60968)
The information in this article applies to:
- Microsoft Basic Professional Development System for MS-DOS 7.0
- Microsoft Basic Professional Development System for MS-DOS 7.1
This article was previously published under Q60968 SUMMARY
The QuickBasic Extended environment (QBX.EXE) can use up to 16 MB
(megabytes) of Lotus-Intel-Microsoft (LIM) 4.0 expanded memory
under MS-DOS. If the expanded memory is available, QBX.EXE
automatically stores in it SUBs, FUNCTIONs, and module-level code
units that are no greater than 16K in size. If QBX.EXE is invoked with
the /Ea switch, arrays that are no greater than 16K in size are also
stored in expanded memory.
In QBX.EXE in Basic PDS version 7.00, the memory is allocated in 16K
pages; for example, a 2K procedure consumes 16K and wastes 14K (16K
minus 2K) of expanded memory. Also, when one or more SUBs or FUNCTIONs
are stored in expanded memory, QBX.EXE makes a one-time allocation of
32K (two 16K pages) in expanded memory as overhead for its own
internal tables.
QBX.EXE in Basic PDS version 7.10 is enhanced so that memory is
allocated in 1K pages; for example, a 1K procedure or array takes up
1K, thus using expanded memory much more efficiently than in QBX.EXE
7.00.
This article applies to Microsoft Basic Professional Development
System (PDS) versions 7.00 and 7.10 for MS-DOS.
MORE INFORMATIONExamples of Expanded Memory Usage in QBX.EXE 7.00
As an example for Basic PDS 7.00, suppose QBX.EXE is run on a machine
for which FRE(-3) reports that 2720K of expanded memory is available.
When the first module-level statement is entered, FRE(-3) would then
return 2704K, 16K less. When the first SUB or FUNCTION is created
after that, FRE(-3) would return 2656K, 48K less -- 16K for the SUB or
FUNCTION itself and 32K for QBX.EXE's internal tables.
When SUBs, FUNCTIONs, module-level code units, or arrays (if /Ea is
used) are deleted, QBX.EXE deallocates the expanded memory they were
using. The tables, however, will not be deallocated unless New Program
is chosen from the File menu.
In 7.00, a single-element integer array takes the same expanded memory
space (16K) as an array with 8192 elements. Likewise, a SUB with a
single PRINT statement takes the same space (16K) as a large SUB with
hundreds of statements. (This is no longer true in 7.10, where
expanded memory usage is more efficient.)
To use expanded memory to its best potential in the QBX.EXE 7.00
environment, you should try to make your SUBs as close to the 16K
limit as possible without exceeding it. (This is not necessary in
7.10.) The size of the SUBs (in kilobytes) is listed in the View Subs
(F2) dialog box to the right of each SUB.
Likewise, arrays in QBX.EXE 7.00 will use expanded memory more
efficiently if they are dimensioned to be just under the 16K page
size. (This is not necessary in 7.10.)
REFERENCES
Microsoft Basic Professional Development System (PDS) versions 7.00
and 7.10 offer expanded memory support under the Lotus-Intel-Microsoft
version 4.0 Expanded Memory Specification (LIM 4.0 EMS) for code and
data in the QBX.EXE environment under MS-DOS. Earlier versions do not
offer any expanded memory support. LIM 4.0 EMS support is discussed in
the "Microsoft Basic 7.0: Getting Started" manual and in the
"Microsoft Basic 7.1: Getting Started" manual.
To be compatible with Basic PDS 7.00 or 7.10, the expanded-memory
device driver must observe the LIM 4.0 EMS.
| Modification Type: | Minor | Last Reviewed: | 8/16/2005 |
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| Keywords: | KB60968 |
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