Bitfields for feature byte 1:
Bit(s)	Description	)
 7	DMA channel 3 used by hard disk BIOS
 6	2nd interrupt controller (8259) installed
 5	Real-Time Clock installed
 4	INT 15/AH=4Fh called upon INT 09h
 3	wait for external event (INT 15/AH=41h) supported
 2	extended BIOS area allocated (usually at top of RAM)
 1	bus is Micro Channel instead of ISA
 0	system has dual bus (Micro Channel + ISA)
SeeAlso: #00509,#00511