Q64101: Description of Expanded Memory Switches for BASIC PDS 7.10

Article: Q64101
Product(s): See article
Version(s): 7.00 7.10
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S900503-164 | mspl13_basic
Last Modified: 15-JAN-1991

This article describes the purpose and use of the switches that allow
you to configure use of expanded memory (according to the LIM 4.0
Expanded Memory Specification [EMS]) in BASIC PDS 7.00 and 7.10.
Especially important is the description of the /Es switch and its
relationship to the other expanded memory switches.

This information applies to Microsoft BASIC Professional Development
System versions 7.00 and 7.10 for MS-DOS.

Saving and Restoring the Expanded Memory State
----------------------------------------------

By default, QBX.EXE and programs compiled with BC.EXE 7.00 or 7.10
will only perform the minimum saving and restoring of the expanded
memory state necessary to allow the program to work properly. This
assumes that no third-party code using expanded memory is present. To
get more than this minimal amount of expanded memory saving/restoring,
you must specify /Es upon loading QBX or when compiling programs with
BC.EXE. This is by design. If BASIC always saved and restored the
state of expanded memory, the save/restore operations would have a
significant speed impact on ISAM and on Quick library (.QLB) calling.
The purpose of the /Es switch is to allow programs to use third-party
code that uses expanded memory. The trade-off is a degradation in
speed.

Table of Expanded Memory Switches and Where You Can Use Them
------------------------------------------------------------

   Use With    Switch Name    Switch Purpose
   --------    -----------    --------------

   QBX only    /Ea            Arrays > 512 bytes but < 16K in
                              expanded memory. Default: No arrays in
                              expanded memory.

   QBX only    /E:n           n = amount in kilobytes of expanded
                              memory QBX will use. 0 means QBX uses no
                              expanded memory. Default: Use all
                              available expanded memory.

   QBX and BC  /Es            Enable saving/restoring of expanded
                              memory state.

   PROISAM(D)  /Ie:n          Reserves n kilobytes of expanded memory
                              for other applications (such as QBX).
                              ISAM will only use 1.2 megabytes of
                              expanded memory maximum.

Examples: Use of Switches, Their Effects, and How They Interact
---------------------------------------------------------------

QBX /E:0
--------

- Causes QBX to disable use of expanded memory code storage.

- If the program has ISAM using expanded memory, it is assumed there
  is no third-party code accessing expanded memory. With /E:0, the
  default for QBX is not to save/restore the expanded memory state on
  ISAM use. This maximizes the speed of ISAM performance.

QBX /E:0 /Es
------------

- Save/restore operations occur on any ISAM statements or QLB calls.
  You would use this combination if you are loading QLBs that use
  expanded memory and you are also using ISAM that is using expanded
  memory.

QBX /E:N and N Is Nonzero
-------------------------

- The expanded memory state is not saved/restored on QLB calls.

- Save/restore operations occur on ISAM calls when both QBX and ISAM
  are sharing expanded memory.

- It is assumed there are no QLBs using expanded memory.

QBX /Es or QBX /E:N /Es
-----------------------

- Forces save/restore operations on QLB calls and ISAM statements.

- This would be used if you are using QBX and calling QLB routines that
  access expanded memory.

BC with No Expanded Memory Management Switches, No Overlays, No ISAM
--------------------------------------------------------------------

- The expanded memory state is not saved/restored.

- Third-party routines accessing expanded memory should work
  correctly.

BC with Overlays That Will Load from Expanded Memory
----------------------------------------------------

- Expanded memory will be used by compiled code in the overlays.

- The default is to save/restore expanded memory on all ISAM
  statements in a program that uses overlays.

- This could still cause problems if third-party library routines that
  use expanded memory are called.

BC /Es with Overlays and ISAM
-----------------------------

- Expanded memory will be saved/restored on ISAM statements.

- Always use /Es when making mixed-language calls to routines that use
  expanded memory as well.

BC /Es Without Expanded Memory Overlays, but with ISAM
------------------------------------------------------

- /Es always causes save/restore operations on ISAM statements when
  ISAM is using expanded memory.

- You would use this switch if the program uses ISAM, ISAM is using
  expanded memory, and there are mixed-language CALLs to routines
  that use expanded memory.

  Note: /Es will not cause save/restore operations on ISAM statements
  if ISAM is NOT using expanded memory.

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