MSC: unsigned _dos_getdiskfree(unsigned drv,struct diskfree_t *spc)

	- prototype in dos.h

	- drive =  1 = A:, 2 = B:, 3 = C:, ...
	- spc = structure to contains disk status information
	- returns 0 on success or DOS error code on failure

	struct diskfree_t
	   {
	   unsigned total_clusters;		- count of all disk clusters
	   unsigned avail_clusters;		- free unallocated clusters
	   unsigned sectors_per_cluster;
	   unsigned bytes_per_sector;
	   };

	- Turbo C uses getdfree()
	- see	INT 21,36