diff --git a/Makefile b/Makefile
index ad0ec47..0a6c2ae 100644
--- a/Makefile
+++ b/Makefile
@@ -6,11 +6,15 @@ PYTHON = python3
 
 all: ponydos.img
 
-FS_FILES = bg.bin shell.bin
+FS_FILES = wallpaper.bin shell.bin
 
 ponydos.img: ponydos.bin $(FS_FILES)
 	$(PYTHON) assemble_floppy.py $@ ponydos.bin $(FS_FILES)
 
+ponydos.bin: ponydos.inc
+
+shell.bin: ponydos.inc
+
 .asm.bin:
 	$(NASM) -fbin -o $@ $<
 
diff --git a/debug.inc b/debug.inc
new file mode 100644
index 0000000..f7be956
--- /dev/null
+++ b/debug.inc
@@ -0,0 +1,39 @@
+hexprint16:
+	xchg ah, al
+	call hexprint8
+	xchg ah, al
+
+hexprint8:
+	push ax
+	push cx
+	mov cl, 4
+	shr al, cl
+	call hexprint4
+	pop cx
+	pop ax
+
+hexprint4:
+	push ax
+	and al, 0xf
+	cmp al, 10
+	jb .digit09
+
+	add al, 'a' - '0' - 10
+
+	.digit09:
+	add al, '0'
+	mov ah, 0x0e
+	int 0x10
+	pop ax
+	ret
+
+hang:
+	hlt
+	jmp hang
+
+wait_key:
+	push ax
+	xor ah, ah
+	int 0x16
+	pop ax
+	ret
diff --git a/ponydos.asm b/ponydos.asm
index 6c41154..09647b6 100644
--- a/ponydos.asm
+++ b/ponydos.asm
@@ -1,3 +1,5 @@
+%include "ponydos.inc"
+
 cpu 286
 bits 16
 
@@ -6,13 +8,20 @@ org 0x7c00
 COLUMNS equ 80
 ROWS equ 25
 
-WALLPAPER equ 0x500
-
 DIRENTS equ 0x2000
 DIRENT_SIZE equ 32
 FILE_MAX_SIZE equ 128
 
 jmp 0:start
+
+; Thunks for application programs to use
+; 0x7c05
+call open_file
+retf
+; 0x7c09
+call read_sectors
+retf
+
 start:
 	cld
 
@@ -64,13 +73,6 @@ initialize_mouse:
 
 	.done:
 
-load_wallpaper:
-	mov si, wallpaper_name
-	call open_file
-	mov bx, WALLPAPER
-	call read_sectors
-	; TODO: error management? Surely this works...
-
 load_shell:
 	push word 0x1000
 	pop es
@@ -78,7 +80,9 @@ load_shell:
 	call open_file
 	xor bx, bx
 	call read_sectors
+	; TODO: error management? Surely this works...
 
+	xor ax, ax ; WM_INITIALIZE
 	call 0x1000:0
 
 initialize_screen:
@@ -124,7 +128,7 @@ mainloop:
 draw_wallpaper:
 	pusha
 
-	mov si, WALLPAPER
+	mov si, GLOBAL_WALLPAPER
 	xor di, di
 	mov cx, 80*25
 	rep movsw
@@ -227,8 +231,7 @@ modify_sector:
 ; Filesystem
 ; ------------------------------------------------------------------
 
-wallpaper_name: db 'bg.bin', 0
-shell_name: db 'shell.bin', 0
+shell_name db 'shell.bin', 0
 
 ; in:
 ;  ds:si = file name
@@ -387,44 +390,6 @@ mouse_handler:
 	popa
 	retf
 
-; ------------------------------------------------------------------
-; Debug routines
-; ------------------------------------------------------------------
-
-%if 0
-hexprint16:
-	xchg ah, al
-	call hexprint8
-	xchg ah, al
-
-hexprint8:
-	push ax
-	push cx
-	shr al, 4
-	call hexprint4
-	pop cx
-	pop ax
-
-hexprint4:
-	push ax
-	and al, 0xf
-	cmp al, 10
-	jb .digit09
-
-	add al, 'a' - '0' - 10
-
-	.digit09:
-	add al, '0'
-	mov ah, 0x0e
-	int 0x10
-	pop ax
-	ret
-
-hang:
-	hlt
-	jmp hang
-%endif
-
 ; ------------------------------------------------------------------
 ; Padding and boot sector signature
 ; ------------------------------------------------------------------
diff --git a/ponydos.inc b/ponydos.inc
new file mode 100644
index 0000000..5273276
--- /dev/null
+++ b/ponydos.inc
@@ -0,0 +1,8 @@
+PONYDOS_SEG equ 0
+
+SYS_OPEN_FILE equ 0x7c05
+SYS_READ_SECTORS equ 0x7c09
+
+GLOBAL_WALLPAPER equ 0x500
+
+WM_INITIALIZE equ 0
diff --git a/shell.asm b/shell.asm
index dfd51d1..ca0f379 100644
--- a/shell.asm
+++ b/shell.asm
@@ -1,2 +1,52 @@
+%include "ponydos.inc"
+
+cpu 8086
+bits 16
+
+
 org 0
-retf
+
+process_event:
+	push ax
+	push bx
+	push cx
+	push dx
+	push si
+	push di
+	push bp
+	push ds
+	push es
+
+	mov bp, cs
+	mov ds, bp
+	mov es, bp
+
+	cmp ax, WM_INITIALIZE
+	jne .not_initialize
+	call initialize
+	.not_initialize:
+
+	pop es
+	pop ds
+	pop bp
+	pop di
+	pop si
+	pop dx
+	pop cx
+	pop bx
+	pop ax
+	retf
+
+initialize:
+	; Set wallpaper
+	mov si, wallpaper_name
+	call PONYDOS_SEG:SYS_OPEN_FILE
+
+	mov bp, PONYDOS_SEG
+	mov es, bp
+	mov bx, GLOBAL_WALLPAPER
+	call PONYDOS_SEG:SYS_READ_SECTORS
+
+	ret
+
+wallpaper_name db 'wallpaper.bin', 0
diff --git a/bg.ansi b/wallpaper.ansi
similarity index 100%
rename from bg.ansi
rename to wallpaper.ansi