1                                  ; boot1.asm   stand alone program for floppy boot sector
     2                                  ; Compiled using            nasm -f bin boot1.asm
     3                                  ; Written to floppy with    dd if=boot1 of=/dev/fd0
     4                                  	
     5                                  ; Boot record is loaded at 0000:7C00,
     6                                  	ORG 7C00h
     7                                  ; load message address into SI register:
     8 00000000 8D36[2500]              	LEA SI,[msg]
     9                                  ; screen function:
    10 00000004 B40E                    	MOV AH,0Eh
    11 00000006 8A04                    print:  MOV AL,[SI]         
    12 00000008 3C00                    	CMP AL,0         
    13 0000000A 7405                    	JZ done		; zero byte at end of string
    14 0000000C CD10                    	INT 10h		; write character to screen.    
    15 0000000E 46                           	INC SI         
    16 0000000F EBF5                    	JMP print
    17                                  
    18                                  ; wait for 'any key':
    19 00000011 B400                    done:   MOV AH,0       
    20 00000013 CD16                        	INT 16h		; waits for key press
    21                                  			; AL is ASCII code or zero
    22                                  			; AH is keyboard code
    23                                  
    24                                  ; store magic value at 0040h:0072h to reboot:
    25                                  ;		0000h - cold boot.
    26                                  ;		1234h - warm boot.
    27 00000015 B84000                  	MOV  AX,0040h
    28 00000018 8ED8                    	MOV  DS,AX
    29 0000001A C70672000000            	MOV  word[0072h],0000h   ; cold boot.
    30 00000020 EA0000FFFF              	JMP  0FFFFh:0000h	 ; reboot!
    31                                  
    32 00000025 57656C636F6D652C20-     msg 	DB  'Welcome, I have control of the computer.',13,10
    33 0000002E 49206861766520636F-
    34 00000037 6E74726F6C206F6620-
    35 00000040 74686520636F6D7075-
    36 00000049 7465722E0D0A       
    37 0000004F 507265737320616E79-     	DB  'Press any key to reboot.',13,10
    38 00000058 206B657920746F2072-
    39 00000061 65626F6F742E0D0A   
    40 00000069 286166746572207265-     	DB  '(after removing the floppy)',13,10,0
    41 00000072 6D6F76696E67207468-
    42 0000007B 6520666C6F70707929-
    43 00000084 0D0A00             
    44                                  ; end boot1