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Q68927: Effect of Spawning COMMAND.COM on the Environment

Article: Q68927
Product(s): Microsoft Disk Operating System
Version(s): MS-DOS:3.x,4.x,5.x,6.0,6.2,6.21,6.22
Operating System(s): 
Keyword(s): 
Last Modified: 17-DEC-2000

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The information in this article applies to:

- Microsoft MS-DOS operating system versions 3.1, 3.2, 3.21, 3.3, 3.3a, 4.0, 4.01, 5.0, 5.0a, 6.0, 6.2, 6.21, 6.22 
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SUMMARY
=======

If you spawn another COMMAND.COM, the child COMMAND.COM has its own environment
space allocated to it. The size of this environment space is at least the
minimum environment size of 160 bytes. If you start the child COMMAND.COM with
the /e:<size> switch, the child's environment space is equal to the
indicated <size> in bytes, rounded up to the nearest 16-byte boundary. The
maximum allowable environment size is 32,768 bytes.

A copy of the parent process's environment variables are placed in the child's
environment space. If the parent's environment variables exceed the space
allocated to the child, the child's environment space is automatically increased
to allow for the parent's variables. Once again, the environment space is
rounded up to the nearest 16-byte boundary. Any changes made to the child's
environment have no effect on the parent's environment.

MORE INFORMATION
================

By using the /e:<size> switch on COMMAND.COM, you can force the allocation
of that much memory to the environment. In MS-DOS versions 5.0 and later, a
default environment space of 256 bytes is allocated if no /e switch is used
(lesser amounts can be specified using the /e:<size> switch). In earlier
MS-DOS versions, 160 bytes is the default. The environment can grow beyond the
allocated size, but this can occur only if there is free (unallocated) memory
available that is contiguous to the currently allocated environment block.

Additional query words: 6.22 3.20 3.21 3.30 3.30a 4.00 4.01 4.01a 5.00 5.00a 6.00 6.20

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Keywords          :  
Technology        : kbMSDOSSearch kbMSDOS321 kbMSDOS400 kbMSDOS320 kbMSDOS330a kbMSDOS621 kbMSDOS622 kbMSDOS620 kbMSDOS600 kbMSDOS310 kbMSDOS500 kbMSDOS330 kbMSDOS401 kbMSDOS500a
Version           : MS-DOS:3.x,4.x,5.x,6.0,6.2,6.21,6.22

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