Here is a deep dive into the mechanics, the code, and the history behind clearing the screen in x86 environments. The Concept: What Does "CLS" Actually Do?
To clear the screen, programmers use the "Scroll Window Up" function ( AH = 06h ). By setting the number of lines to scroll to zero, the BIOS clears the specified region. cls magic x86
mov ax, 0B800h ; Point to video memory segment mov es, ax xor di, di ; Start at offset 0 mov ax, 0720h ; 07 = White/Black, 20 = Space character mov cx, 2000 ; 80 * 25 = 2000 words rep stosw ; "Magic" happens here: Repeat storing AX into ES:DI Use code with caution. Here is a deep dive into the mechanics,
If you are writing a bootloader or a hobbyist OS, you must implement your own screen-clearing routine to handle kernel output. By setting the number of lines to scroll
(the background and foreground colors). Resetting the cursor position to the top-left corner (0,0). Method 1: The BIOS Interrupt (The "Standard" Way)
After this, you must manually move the cursor back to the start:
mov ah, 06h ; Scroll up function mov al, 00h ; AL = 0 means clear the entire window mov bh, 07h ; BH = Attribute (07h is white text on black background) mov cx, 0000h ; CH, CL = Upper left corner (0,0) mov dx, 184Fh ; DH = 24 (Rows), DL = 79 (Cols) int 10h ; Call BIOS Use code with caution.