diff --git a/recipes/z80mbc2/README.md b/recipes/z80mbc2/README.md
index ed0fe64..0290ac7 100644
--- a/recipes/z80mbc2/README.md
+++ b/recipes/z80mbc2/README.md
@@ -8,7 +8,7 @@ Collapse OS on it rather simple.
 
 In this recipe, we're going to run Collapse OS on the Z80-MBC2, interfacing
 through its serial port. We're going to use the MBC's API to implement BLK on
-the SD card. (the BLK part isn't done yet. TODO)
+the SD card.
 
 ### Gathering parts
 
@@ -25,6 +25,16 @@ Running `make` will yield `os.bin` which is what we want.
 Mount the SD card on your modern computer and copy `os.bin` as `autoboot.bin`,
 overwriting the binary that was previously there.
 
+We also have to copy the blkfs over. This is done by using IOS' drive system.
+Each `DSxNyy.DSK` file on the card is a drive, each drive has 512 track of 32
+sectors of 512 bytes, so one drive is plenty for our needs. Collapse OS
+hardcodes drive 0.
+
+Each drive is part of a set. IOS theoretically supports up to 10 sets, but the
+binary shipped by default only accepts 4. You have to overwrite an existing set.
+I used set 3. So, copy `blkfs` to file `DS3N00.DSK`. If you want, you can change
+the name of the set by changing the contents of `DS3NAM.DAT`.
+
 Put back the SD card in the Z80-MBC2 and power it up by connecting the FTDI
 adapter to it (red: VCC, black: GND, green: TX, white: RX).
 
@@ -34,7 +44,10 @@ the Z80-MBC2 appears to be hardcoded to 115200.
 
 Then, enable IOS program selection by holding RESET and USER at the same time,
 wait 2 seconds, releasing RESET, wait 2 seconds, releasing USER. You should then
-be given a 1-8 choice, with 4 being "Autoboot". Type 4.
+be given a 1-8 choice.
+
+You begin by selecting the proper disk set, which is through choice 8, then you
+select the Autoboot binary through choice 4.
 
 You are now in Collapse OS.
 
diff --git a/recipes/z80mbc2/xcomp.fs b/recipes/z80mbc2/xcomp.fs
index db504f2..f4a0e16 100644
--- a/recipes/z80mbc2/xcomp.fs
+++ b/recipes/z80mbc2/xcomp.fs
@@ -10,10 +10,30 @@ CODE (key)
     BEGIN, 1 INAn, A INCr, JRZ, AGAIN,
     A DECr, PUSHA,
 ;CODE
+: _sel ( sec )
+( 32 sectors per track, 512 tracks per disk )
+    32 /MOD ( addr sec trk )
+    0x0a ( seltrk ) 1 PC! 0 PC! 0 0 PC! ( addr sec )
+    0x0b ( selsec ) 1 PC! 0 PC! ( addr ) ;
+: _ ( addr )
+    ( get 512 bytes )
+    0x86 ( readsec ) 1 PC!
+    512 0 DO 0 PC@ SWAP C!+ LOOP DROP
+;
+: FD@ 2 * DUP _sel BLK( _ 1+ _sel BLK( 512 + _ ;
+: _ ( addr )
+    ( write 512 bytes )
+    0x0c ( writesec ) 1 PC!
+    512 0 DO C@+ 0 PC! LOOP DROP
+;
+: FD! 2 * DUP _sel BLK( _ 1+ _sel BLK( 512 + _ ;
+: FD$ ( select disk 0 )
+    0x09 ( seldisk ) 1 PC! 0 0 PC! ( sel disk 0 )
+;
 380 LOAD  ( xcomp core high )
 (entry) _
 ( Update LATEST )
 PC ORG @ 8 + !
-," CURRENT @ HERE ! " EOT,
+," CURRENT @ HERE ! BLK$ FD$ ' FD@ BLK@* ! ' FD! BLK!* ! " EOT,
 ORG @ 256 /MOD 2 PC! 2 PC!
 H@ 256 /MOD 2 PC! 2 PC!