Format of DOS 2.x disk buffer:
Offset	Size	Description	)
 00h	DWORD	pointer to next disk buffer, offset = FFFFh if last
		least-recently used buffer is first in chain
 04h	BYTE	drive (0=A, 1=B, etc), FFh if not in use
 05h  3 BYTEs	unused??? (seems always to be 00h 00h 01h)
 08h	WORD	logical sector number
 0Ah	BYTE	number of copies to write (1 for non-FAT sectors)
 0Bh	BYTE	sector offset between copies if multiple copies to be written
 0Ch	DWORD	pointer to DOS Drive Parameter Block (see #01395 at AH=32h)
 10h		buffered data
SeeAlso: #01650,#01652,#01653,#01655