Int 2F Fn 1607  C - Ms Windows - "pagefile" Virtual Device - Get Lock Byt  [W]

   AX = 1607h
   BX = 0021h (PageFile VxD ID)
   CX = 0000h

Return: AX = status
       0000h success
       ES:DI -> cache lock byte in disk cacher
       other no disk cache or unsupported

Notes: PageFile issues this call on real-mode initialization in order to allow
     disk caches to provide it with a byte which it can use to temporarily
     lock the disk cache; VMPOLL also issues this call, so it is made
     twice each time Windows starts up
   if this call fails, PageFile falls back to other techniques for locking
     the disk cache

See Also: AX=1607h"CALL OUT API"