diff --git a/io.asm b/io.asm
index b2f5f66..f4dec7e 100644
--- a/io.asm
+++ b/io.asm
@@ -26,21 +26,21 @@ assume cs:iogroup, ds:iogroup, es:iogroup
 org 0
 
 ; Jump table
-jmp init
-jmp status
-jmp getch
-jmp putch
-jmp unimplemented ; Output to printer
-jmp unimplemented ; Serial read
-jmp unimplemented ; Serial write
-jmp diskread
-jmp diskwrite
-jmp diskchange
-jmp setdate
-jmp settime
-jmp gettime
-jmp flush
-jmp mapdev
+jmp init ; 0000
+jmp status ; 0003
+jmp getch ; 0006
+jmp putch ; 0009
+jmp unimplemented ; 000c Output to printer
+jmp unimplemented ; 000f Serial read
+jmp unimplemented ; 0012 Serial write
+jmp diskread ; 0015
+jmp diskwrite ; 0018
+jmp near ptr diskchange ; 001b
+jmp setdate ; 001e
+jmp settime ; 0021
+jmp gettime ; 0024
+jmp flush ; 0027
+jmp near ptr mapdev ; 002a
 
 init:
 	cld
@@ -70,13 +70,39 @@ init:
 
 	call dosinit
 
-	mov al, 'c'
-	jmp error
+	; Memory for command.com is at ds, save for later and revert ds
+	push ds
+	mov ax, cs
+	mov ds, ax
+
+	; Open command.com
+	mov dx, offset iogroup:command_fcb
+	mov ah, 0fh
+	int 21h
+
+	test al, al
+	jnz open_error
+
+	mov al, '+'
+	jmp unfinished
+
+	open_error:
+		mov al, '-'
+
+	unfinished:
+		mov ah, 0eh
+		int 10h
+		jmp hang
 
 ; OUT:
 ;  al = character if any
 ;  zf = there were no characters
 status proc far
+	push ax
+	mov ax, 0e00h + 's'
+	int 10h
+	pop ax
+	call far_caller
 	; TODO: Implement
 	xor ax, ax
 	test ax, ax
@@ -97,15 +123,164 @@ putch proc far
 	ret
 putch endp
 
-diskread:
-	mov al, 'r'
-	jmp error
+; IN:
+;  al = driver number
+;  ds:bx = buffer
+;  cx = number of sectors to read
+;  dx = LBA of first sector
+; OUT:
+;  TODO: Document
+diskread proc far
+	push ax
+	mov ax, 0e00h + 'r'
+	int 10h
+	pop ax
+	call far_caller
+
+	push es
+	push ax
+	push bx
+	push cx
+	push dx
+	push di
+
+	; Save driver number
+	push ax
+
+	; BIOS uses es:bx instead of ds:bx
+	mov ax, ds
+	mov es, ax
+
+	mov ax, dx
+
+	; Put drive(r) number in dl
+	pop dx
+
+	sector_read_loop:
+		jcxz ret_diskread
+
+		mov di, 3 + 1 ; 3 retries, + 1 since we dec first
+
+		try_sector_read:
+			push ax
+			push cx
+
+			call chs
+
+			mov ah, 2
+			mov al, 1
+			int 13h
+
+			jnc sector_read_success
+
+			dec di
+			jz sector_read_fail
+			pop cx
+			pop ax
+			jmp try_sector_read
+
+		sector_read_fail:
+			pop cx
+			pop ax
+
+			pop di
+			pop dx
+			pop ax ; Would be cx, don't overwrite
+			pop bx
+			pop ax
+			pop es
+
+			mov al, 12 ; TODO: Don't hardcode
+			ret
+
+		sector_read_success:
+			pop cx
+			pop ax
+			dec cx
+			inc ax
+			add bx, 512
+			jmp sector_read_loop
+
+	ret_diskread:
+		pop di
+		pop dx
+		pop cx
+		pop bx
+		pop ax
+		pop es
+
+		ret
+
+diskread endp
+
+; IN:
+;  ax = LBA
+; OUT:
+;  ch = cylinder
+;  cl = sector & 2 high bits of cylinder
+;  dh = head
+chs proc
+	push ax
+	push dx
+
+	xor dx, dx
+	; cylinder (track) - head - sector
+	; cylinder = LBA / sectorspertrack / heads
+	; head = LBA / sectorspertrack % heads
+	; sector = LBA % sectorspertrack + 1
+	div cs:sectorspertrack
+	; ax = LBA / sectorspertrack
+	; dx = LBA % sectorspertrack
+
+	; sector
+	mov cl, dl
+	inc cl
+
+	xor dx, dx
+	div cs:heads
+	; ax = LBA / sectorspertrack / heads
+	; dx = LBA / sectorspertrack % heads
+
+	; head
+	mov dh, dl
+
+	; cylinder (track)
+	mov ch, al
+	;shr ax, 1
+	;shr ax, 1
+	;and al, 0c0h
+	;or cl, al
+
+	mov ax, dx
+	pop dx
+	mov dh, ah
+	pop ax
+
+	ret
+chs endp
+
 diskwrite:
 	mov al, 'w'
 	jmp error
-diskchange:
-	mov al, 'c'
-	jmp error
+
+; IN:
+;  al = drive
+; OUT:
+;  ah = -1 different / 0 dunno / 1 same
+;  cf = 0 -> al = driver num
+;  cf = 1 -> al = disk error code
+diskchange proc far
+	push ax
+	mov ax, 0e00h + 'd'
+	int 10h
+	pop ax
+	call far_caller
+	; TODO: Implement
+	mov ax, 0100h
+	clc
+	ret
+diskchange endp
+
 setdate:
 	mov al, 'd'
 	jmp error
@@ -119,9 +294,15 @@ flush:
 	mov al, 'f'
 	jmp error
 
-mapdev:
-	mov al, 'm'
-	jmp error
+mapdev proc far
+	push ax
+	mov ax, 0e00h + 'm'
+	int 10h
+	pop ax
+	call far_caller
+	; TODO: Figure out if this does anything?
+	ret
+mapdev endp
 
 unimplemented:
 	mov al, '@'
@@ -129,6 +310,10 @@ unimplemented:
 error:
 	mov ah, 0eh
 	int 10h
+	mov ah, 0eh
+	mov al, '!'
+	int 10h
+	call far_caller
 
 hang:
 	hlt
@@ -136,10 +321,15 @@ hang:
 
 code ends
 
+; TODO: STRUC?
+
 constants segment
 
+sectorspertrack dw 8 ; TODO: Don't hardcode
+heads dw 2 ; TODO: Don't hardcode
+
 disks_table:
-	db 1 ; 1 drive
+	db 1 ; 1 drive, TODO: Don't hardcode
 
 	db 0 ; Physical drive 0
 	dw offset iogroup:parameters_320k
@@ -154,4 +344,105 @@ parameters_320k:
 
 constants ends
 
+data segment
+
+command_fcb:
+	db 1 ; First drive, TODO: Don't hardcode
+	db "COMMAND COM"
+	db 25 dup (?)
+
+data ends
+
+code segment
+hexprint16 proc
+	xchg al, ah
+	call hexprint8
+	xchg al, ah
+hexprint8 proc
+	rol al, 1
+	rol al, 1
+	rol al, 1
+	rol al, 1
+	call hexprint4
+	rol al, 1
+	rol al, 1
+	rol al, 1
+	rol al, 1
+hexprint4 proc
+	push ax
+
+	and al, 0fh
+	cmp al, 9
+	jbe under_10
+	add al, 'a' - 10 - '0'
+
+under_10:
+	add al, '0'
+	mov ah, 0eh
+	int 10h
+
+	pop ax
+	ret
+hexprint4 endp
+hexprint8 endp
+hexprint16 endp
+newline proc
+	push ax
+	mov ax, 0e0dh
+	int 10h
+	mov ax, 0e0ah
+	int 10h
+	pop ax
+	ret
+newline endp
+space proc
+	push ax
+	mov ax, 0e20h
+	int 10h
+	pop ax
+	ret
+space endp
+
+far_caller proc
+	push ax
+	push bx
+	mov bx, sp
+	mov ax, [ss:bx + 8]
+	call hexprint16
+	mov al, ':'
+	mov ah, 0eh
+	int 10h
+	pop bx
+	pop ax
+
+near_caller proc
+	push ax
+	push bx
+	mov bx, sp
+	mov ax, [ss:bx + 6]
+	call hexprint16
+	call space
+	pop bx
+	pop ax
+	ret
+near_caller endp
+far_caller endp
+
+logaddr proc
+	push ax
+	push bx
+	mov al, '>'
+	mov ah, 0eh
+	int 10h
+	mov bx, sp
+	mov ax, [ss:bx + 4]
+	call hexprint16
+	call space
+	pop bx
+	pop ax
+	ret
+logaddr endp
+
+code ends
+
 end