INT 2F C - MS Windows - "PageFile" VIRTUAL DEVICE - GET LOCK BYTE
	AX = 1607h
	BX = 0021h (PageFile VxDA virtual device driver for Windows 3.x or 95.	So called because nearly all of the Windows 3.0 drivers had names of the form "VdeviceD". See also device driver. 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
SeeAlso: AX=1607h"CALL OUT API(Application Program[ming] Interface) The defined set of calls which a program may make to interact with or request services of the operating system or environment under which it is running.  Because the inputs and outputs of the calls are well-defined, a program using the API can continue using the identical calls even if the internal organization of the program providing the API changes."