CHAPTER 3. BOOT SECTOR PROGRAMMING (IN 16-BIT REAL
MODE) 14
Figure 3.4: Typical lower memory layout after boot.
data for a character, then we will try to print out that character on the screen. To do
this we need to figure out its absolute memory address, so we can load it intoaland get
BIOS to print it, as in the last exercise.
;
; A simple boot sector program that demonstrates addressing.
;
mov ah, 0x0e ; int 10/ah = 0eh -> scrolling teletype BIOS routine; First attempt
mov al, the_secret
int 0x10 ; Does this print an X?; Second attempt
mov al, [the_secret]
int 0x10 ; Does this print an X?; Third attempt
mov bx, the_secret
add bx, 0x7c
mov al, [bx]
int 0x10 ; Does this print an X?; Fourth attempt