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SUMMARYA well-known method of providing security features for MS-DOS is to install an interrupt handler into the upper area of conventional memory. INT 12h is used to inform MS-DOS that this portion of memory is no longer available for use with MS-DOS applications. For this technique to work with Windows enhanced mode, it is necessary to write a virtual device (VxD) to map the affected memory pages into virtual machines. MORE INFORMATION
When the value in location 40:13 of the BIOS data segment is decreased, MS-
DOS will reserve memory immediately below the 384 kilobyte adapter segment.
The return value from issuing an INT 12h is the new amount of available
memory. Several manufacturers of security software use this technique to
install software prior to starting MS-DOS.
prod(win3) and riplmem Additional query words: 3.0 boot
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