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Q72112: ‘0 Bytes Available Contiguous Extended Memory’

Article: Q72112
Product(s): Microsoft Disk Operating System
Version(s): MS-DOS:4.x,5.0
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 4.0, 4.01, 5.0 
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SUMMARY
=======

The MEM command reports "0 bytes available contiguous extended memory" when
another device driver or program makes a call to extended memory after HIMEM.SYS
is loaded in the CONFIG.SYS file.

For example, a CONFIG.SYS file with following lines

     device=c:\himem.sys
     device=c:\windows\smartdrv.sys <xxxx> <yyyy>

reports 0 (zero) bytes as available contiguous extended memory with the MEM
command (where <xxxx> is the initial cache size and <yyyy> is the
minimum cache size).

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

Available contiguous extended memory is the extended memory available for the
interrupt 15h interface. This memory is not managed by an extended memory
manager (HIMEM.SYS in this example). HIMEM.SYS manages an application's use of
extended memory and the high memory area (HMA). The extended memory manager
prevents programs from simultaneously accessing the same memory area.

HIMEM.SYS versions 2.04 and 2.60 have no switch to allocate extended memory to
the interrupt 15 interface.

HIMEM.SYS version 2.77, which is shipped with MS-DOS version 5.0, contains an
added /INT15=xxxx switch. This switch allocates a specified amount of extended
memory (in kilobytes) for the interrupt 15h interface. Programs that use
extended memory directly and recognize vdisk headers can use the memory provided
by the /INT15= switch. For more information, refer to the version 5.0 "MS-DOS
User's Guide and Reference."

The programs accessing extended memory using the interrupt 15h call do not get
any access to extended memory if HIMEM.SYS is loaded during system startup.
HIMEM.SYS takes control of all the extended memory if no other device drivers
are loaded before HIMEM.SYS during system startup.

If a program is making an interrupt 15h call to access extended memory, do not
load HIMEM.SYS (version 2.04 or 2.60). Not loading HIMEM.SYS gives access to
extended memory through the interrupt 15h call.

For more information on how the MEM command reports, query on the following
words:

  " MEM and command and extended and memory " (without the quotation marks)

Additional query words: 4.x 5.00 noupd

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Keywords          :  
Technology        : kbMSDOSSearch kbMSDOS400 kbMSDOS500 kbMSDOS401
Version           : MS-DOS:4.x,5.0

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