How to Reboot Your Machine Within a MASM Application

• Microsoft Macro Assembler for MS-DOS, version 5.0, 5.1, 5.1a, 6.0, 6.0a, and 6.0b

SUMMARY

You can perform a complete reboot (cold boot) on an 8086-based machine by jumping to the address FFFF:0000. This action also reboots many 80286 and 80386 machines. The address contains a jump instruction that leads to the machine's initialization code. For this method to succeed, your machine must be in real-mode operation.

MORE INFORMATION

To prevent a memory check on IBM and many compatibles (warm boot), you should store the value 0 x 1234 in the memory location at 0040:0072. On 100-percent IBM BIOS compatible machines, an alternative method is to call int 19h instead of jumping to the address mentioned above.

Sample Code

; Assemble options needed: none

.MODEL small

.CODE

Start:

    mov ax, @data                 ; Load ds with data segment
    mov ds, ax

    mov ax, 40h                   ; These three lines cause a memory
    mov es, ax                    ; test NOT to be performed. To
    mov WORD PTR es:[72h], 1234h  ; do a memory test, remove them.

    jmp DWORD PTR b_vec           ; Jump to the reboot address

b_vec   DW 00000h                 ; Offset of reboot vector
        DW 0FFFFh                 ; Segment of reboot vector

END Start