INT 45 - Acorn BBC Master 512 - "OSFILE" - READ/WRITE FILE OR DIRECTORY INFO
	AL = function
	    00h save block of memory as file
	    01h update directory entry for existing file
	    02h set load address for existing file
	    03h set execution address for existing file
	    04h set attributes for existing file
	    05h read directory
	    06h delete file
	    FFh load file
	DS:BX -> control block (see #03201)
Return: FLAGS destroyed
	AL = file type
	    00h not found
	    01h file found
	    02h directory found
	    FFh protected file
SeeAlso: INT 40"Acorn",INT 41"Acorn",INT 44"Acorn",INT 46"Acorn"


Format of BBC Master control block:
Offset	Size	Description	(Table 03201)
 00h	WORD	address of CR-terminated filename
 02h	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	load address of file
 06h	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	execution address of file
 0Ah	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	start address of data to save
 0Eh	DWORDDoubleword; four bytes.	 Commonly used to hold a 32-bit segment:offset or selector:offset address.	end address of data to save, or file attributes
		file attributes in low byte (see #03202)
		other three bytes are filing-system specific file attributes


Bitfields for BBC Master file attributes:
Bit(s)	Description	(Table 03202)
 0	no owner read access
 1	no owner write access
 2	not executable by owner
 3	not deletable by owner
 4	no public read access
 5	no public write access
 6	not executable with public access
 7	not deletable with public access