Format of MS-DOS 7.0 HMA memory control block:
Offset	Size	Description	)
 00h	WORD	signature "MS" (4Dh 53h)
 02h	WORD	usage flag???
		0000h free
		else ???
 04h	WORD	size of memory block in bytes (not counting MCB)
 06h	WORD	offset of next memory block in HMA or 0000h
 08h  8 BYTEs	unused (0)
SeeAlso: #01628,#01630,#01632