diff --git a/Makefile b/Makefile
index eef5ab7..b05fd49 100644
--- a/Makefile
+++ b/Makefile
@@ -48,6 +48,8 @@ vga11.com: cp437.bin
 %.bs: boot/%.asm
 	$(NASM) $(NASM_ARGS) -o $@ $<
 
+kernel.bs: kernel/*.asm
+
 # Special case: variations of FAT vbr
 fat1.bs: boot/fat.asm
 	$(NASM) $(NASM_ARGS) -DFAT12 -DCHS -o $@ $<
diff --git a/boot/kernel.asm b/boot/kernel.asm
index 954aa03..4fff9eb 100644
--- a/boot/kernel.asm
+++ b/boot/kernel.asm
@@ -10,8 +10,8 @@
 	%endmacro
 
 	; Far jump via interrupt vector
-	%macro intjump 1
-	jump far [cs:%1*4]
+	%macro intjmp 1
+	jmp far [cs:%1*4]
 	%endmacro
 
 	; stack size
@@ -22,7 +22,7 @@ banner:	db "rdos", 0xA, 0xD, '$'
 	; Alias for Int 21h,AH=0h
 int20h:	xor ah, ah
 	; allow extenders to get away with only hooking 21h
-	jmp [cs:(0x21 * 4)]
+	intjmp 0x21
 
 int21h:	; inside of kernel, direction always goes up
 	; the iret will restore it to the user value later
@@ -48,6 +48,7 @@ iretfl:	push ax
 	pop ax
 	; iret frame: IP CS FLAGS
 iret:	iret
+retf:	retf
 
 	; Subfunction ptr
 	; this is used as extra register in int21h
@@ -171,185 +172,6 @@ getint:	xor bx, bx
 sferr:	stc
 	ret
 
-	; Convert between drive number and BIOS dl
-	; Bidirectional mapping
-	; 0 <-> 0, 1 <-> 1, 2 <-> 0x80, 3 <-> 0x81
-dnconv:	mov cx, 7
-	ror dx, 1
-	rol dl, 1
-dncl:	rcl dl, 1
-	rcr dh, 1
-	loop dncl
-	xchg dh, dl
-	ret
-
-	; Set sector number
-seek:	mov [drvpos], ax
-	mov [drvpos+2], dx
-	ret
-
-	; Read sector from disk
-read:	; this uses the EBIOS extensions
-
-	; qword sector number
-	xor ax, ax
-	push ax
-	push ax
-	mov ax, [cs:drvpos+2]
-	push ax
-	mov ax, [cs:drvpos]
-	push ax
-
-	; dword target buffer
-	mov ax, buffer
-	push cs
-	push ax
-
-	; word number of sectors
-	mov ax, 1
-	push ax
-
-	; size & passing
-	mov di, 0x10
-	push di
-
-	mov si, sp
-	mov ah, 0x42
-	mov dl, [cs:drvnum]
-	call dnconv
-	stc
-	int 0x13
-
-	add sp, di
-	ret
-
-	; Select active drive
-	; IN	dl	drive number A=0, B=1, C=2, ...
-select:	mov [cs:drvnum], dl
-	ret
-	push es
-	xor ax, ax
-	push cs
-	pop es
-	mov si, drvoff
-	stosw
-	stosw
-	stosw
-	stosw
-	pop es
-	call read
-	; load bpb from buffer to bpb
-ldbpb:	push ds
-	push es
-	mov ax, cs
-	mov ds, ax
-	mov es, ax
-	mov si, buffer+0x0B
-	mov di, bpb
-	mov cx, bpb_len
-	rep movsb
-	pop es
-	pop ds
-	ret
-
-
-	; defines for CHS table
-chs_spt: equ 0 ; word sectors per track
-chs_nos: equ 2 ; word number of sides
-chs_po:  equ 4 ; dword partition offset
-chs_siz: equ 8
-
-
-fndchs:	; find CHS table entry
-	; IN	dl	DOS drive number (A=0, B=1, ...)
-	; OUT	cs:si	ptr to chs table entry
-	push ax
-	mov ax, chs_siz
-	mul dl
-	add ax, chstab
-	mov si, ax
-	pop ax
-	ret
-
-	; compare sector number in disk access packet with zero
-	; sets zero flag accordingly
-iszero:	push ax
-	mov ax, [bx]
-	or ax, [bx+2]
-	pop ax
-	ret
-
-	; calculate CHS from dap and CHS table entry
-	; IN	ds:bx	disk access packet
-	;	cs:si	chstab table entry
-	; OUT	cx,dh	chs data for int 13h
-calchs:	push ax
-	; load linear sector number
-	mov dx, [bx+2]
-	mov ax, [bx]
-	; if any word of it is non-zero, we need to do calculation
-	call iszero
-	jz .zero
-	; ax is track number (lba / spt)
-        ; dx is sector (lba % spt) + 1
-	div word [cs:si+chs_spt]
-	inc dx
-	; sector number
-	mov cl, dl
-	; ax is cylinder (track / heads)
-	; dx is head (track % heads)
-	xor dx, dx
-	div word [cs:si+chs_nos]
-	; set up cylinder and head number
-	mov ch, al
-	mov dh, dl
-	pop ax
-	ret
-	; set up CHS data for int 13h for reading sector zero
-.zero:	mov cx, 1 ; C=0, S=1
-	mov dh, 0 ; H=0
-	pop ax
-	ret
-
-	; ABSOLUTE DISK READ / DISK WRITE
-int25h:	mov ah, 2
-	jmp adisk
-int26h:	mov ah, 3
-adisk:	push bp
-	push ds
-	push es
-	mov bp, sp
-	cmp cx, 0xFFFF
-	je .islrg
-
-	; build a disk access packet on the stack
-	push ds ; dword transfer buffer
-	push bx
-	push cx ; word number of sectors
-	push cs ; dword starting sector number (CS always 0)
-	push dx
-
-	; set our freshly created dap as DS:BX
-	mov bx, sp
-	push ss
-	pop ds
-
-.islrg: mov dl, al
-	call fndchs
-	call calchs
-	mov dl, al
-	mov al, [bx+4]
-	mov es, [bx+8]
-	mov bx, [bx+6]
-	int 0x13
-	jc .ret
-
-.ret:	mov sp, bp
-	pop es
-	pop ds
-	pop bp
-retf:	retf
-
 	; DOS IDLE INTERRUPT
 	; Usually hooked by TSRs
 idle:	sti
@@ -370,6 +192,8 @@ fputc:	push ax
 	pop ax
 	iret
 
+	%include "kernel/diskio.asm"
+
 vects:	dw int20h, int21h, retf, retf
 	dw retf, int25h, int26h, int20h
 	dw idle, fputc
@@ -428,11 +252,4 @@ section .bss
 stack:	resw stacks
 	; default int 25h/26h handler use a cache to keep geometry for
 	; the first 4 drives
-chstab:	resw (4*chs_siz)
-
-bpb:	resb bpb_len
-drvnum:	resb 1
-	align 4
-drvoff:	resd 1; partition offset
-drvpos:	resd 1; absolute physical sector number
 buffer:	resb 512
diff --git a/kernel/diskio.asm b/kernel/diskio.asm
new file mode 100644
index 0000000..45d7631
--- /dev/null
+++ b/kernel/diskio.asm
@@ -0,0 +1,112 @@
+	section .bss
+
+chsspt: equ 0 ; word sectors per track
+chsnos: equ 2 ; word number of sides
+chspo:  equ 4 ; dword partition offset
+chssiz: equ 8
+
+chstab: resw (4*chssiz)
+
+	section .text
+
+	; Convert between drive number and BIOS dl
+	; Bidirectional mapping
+	; 0 <-> 0, 1 <-> 1, 2 <-> 0x80, 3 <-> 0x81
+dnconv:	mov cx, 7
+	ror dx, 1
+	rol dl, 1
+dncl:	rcl dl, 1
+	rcr dh, 1
+	loop dncl
+	xchg dh, dl
+	ret
+
+fndchs:	; find CHS table entry
+	; IN	dl	DOS drive number (A=0, B=1, ...)
+	; OUT	cs:si	ptr to chs table entry
+	push ax
+	mov ax, chssiz
+	mul dl
+	add ax, chstab
+	mov si, ax
+	pop ax
+	ret
+
+	; compare sector number in disk access packet with zero
+	; sets zero flag accordingly
+iszero:	push ax
+	mov ax, [bx]
+	or ax, [bx+2]
+	pop ax
+	ret
+
+	; calculate CHS from dap and CHS table entry
+	; IN	ds:bx	disk access packet
+	;	cs:si	chstab table entry
+	; OUT	cx,dh	chs data for int 13h
+calchs:	push ax
+	; load linear sector number
+	mov dx, [bx+2]
+	mov ax, [bx]
+	; if any word of it is non-zero, we need to do calculation
+	call iszero
+	jz .zero
+	; ax is track number (lba / spt)
+        ; dx is sector (lba % spt) + 1
+	div word [cs:si+chsspt]
+	inc dx
+	; sector number
+	mov cl, dl
+	; ax is cylinder (track / heads)
+	; dx is head (track % heads)
+	xor dx, dx
+	div word [cs:si+chsnos]
+	; set up cylinder and head number
+	mov ch, al
+	mov dh, dl
+	pop ax
+	ret
+	; set up CHS data for int 13h for reading sector zero
+.zero:	mov cx, 1 ; C=0, S=1
+	mov dh, 0 ; H=0
+	pop ax
+	ret
+
+	; ABSOLUTE DISK READ / DISK WRITE
+int25h:	mov ah, 2
+	jmp adisk
+int26h:	mov ah, 3
+adisk:	push bp
+	push ds
+	push es
+	mov bp, sp
+	cmp cx, 0xFFFF
+	je .islrg
+
+	; build a disk access packet on the stack
+	push ds ; dword transfer buffer
+	push bx
+	push cx ; word number of sectors
+	push cs ; dword starting sector number (CS always 0)
+	push dx
+
+	; set our freshly created dap as DS:BX
+	mov bx, sp
+	push ss
+	pop ds
+
+.islrg: mov dl, al
+	call fndchs
+	call calchs
+	mov dl, al
+	mov al, [bx+4]
+	mov es, [bx+8]
+	mov bx, [bx+6]
+	int 0x13
+	jc .ret
+
+.ret:	mov sp, bp
+	pop es
+	pop ds
+	pop bp
+	retf