diff --git a/mem.asm b/mem.asm
index e01ef5e..8d03ae6 100644
--- a/mem.asm
+++ b/mem.asm
@@ -14,7 +14,9 @@ mtab_ref:
   ret
 
 ; finds a place for a new item in the mm table
-; out: bx
+; this detects 'empty' slots by the size field being zero
+; in:	ds:si:	pointer to first mtab item
+; out:	bx:	offset for empty slot
 mtab_alloc:
   push ax
   call mtab_ref
@@ -27,6 +29,38 @@ mtab_alloc:
   pop ax
   ret
 
+; splits a mtab item at offset
+; in:  ds:si: pointer mtab item
+;      ax:    split position in 16 byte blocks
+; out: ds:si: pointer to lower half
+;      ds:di: pointer to upper half
+mtab_split:
+  push cx ; remaining memory block length
+  mov cx,[ds:si]
+
+  mov [ds:si],ax ; this resizes the first item
+  sub cx, ax
+
+  push bx
+  call mtab_alloc
+  mov di,bx
+  pop bx
+
+  push si ; backup because movsw increments them
+  push di ; ^
+  push cx ; counter for movsb
+  mov es,ds
+  mov cx,0x08 ; 8 words = 16 bytes
+  rep movsw ; repeat cx times
+  pop cx
+  pop di
+  pop si
+
+  mov [ds:di],cx
+
+  pop cx
+  ret
+
 ; in:  ax: segment
 ;      bh: task id (0 for non-task memory)
 ;      bl: memory type (see enum at top of file)