Q21902: SHELL Can Give "Out of Memory" Error or Fragment Memory

Article: Q21902
Product(s): See article
Version(s): 2.00 2.01 3.00 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom | mspl13_basic
Last Modified: 21-DEC-1989

Question:

Why do I get an "Out of Memory" error when I use the SHELL statement
or the Shell command?

Response:

The SHELL statement does not clean up or compress memory. If not
enough contiguous memory is available (for example, if many CHAIN
statements have been executed, or several dynamic arrays were
allocated then erased), a SHELL statement may fail with an "Out of
memory" error. This includes both the Shell command from the File menu
and also the SHELL statement in a running program.

Also, if you mistakenly install any TSR (terminate and stay resident)
program during a SHELL command, you will fragment memory, which often
results in an "Out of Memory" error. For example, if you run the
QuickBASIC environment, choose the Shell command from the File menu,
install a TSR, EXIT the Shell, Exit the QuickBASIC environment, and
reinvoke the QuickBASIC environment from DOS, then you get an "Out of
Memory" error immediately before you can do anything in the
environment. You must reboot to unfragment DOS memory.

This information applies to Microsoft QuickBASIC Versions 2.00, 2.01,
3.00, 4.00, 4.00b, and 4.50, to Microsoft BASIC Compiler Versions 6.00
and 6.00b for MS-DOS, and to Microsoft BASIC PDS Version 7.00 for
MS-DOS.

TSR programs should NEVER be installed during a SHELL statement or a
Shell from the File menu. Examples of TSR programs are MSHERC.COM
(from QuickBASIC 4.50) and QBHERC.COM (from QuickBASIC 4.00/4.00b and
the BASIC compiler 6.00/6.00b).

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