Description of Expanded Memory Switches for Basic PDS 7.10 (64101)

MORE INFORMATION

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.