'0 Bytes Available Contiguous Extended Memory' (72112)

The information in this article applies to:
    Microsoft MS-DOS operating system 4.0
    Microsoft MS-DOS operating system 4.01
    Microsoft MS-DOS operating system 5.0

This article was previously published under Q72112


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:\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).


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

Modification Type: Major Last Reviewed: 10/13/2003
Keywords: KB72112