BIOS System Descriptor Table (PS/2)

     Offset Size	     Description

	00   word	length of descriptor (8 minimum)
	02   byte	model byte (same as FFFF:E, not reliable)
	03   byte	secondary model byte
	04   byte	BIOS revision level (zero based)
	05   byte	feature information  (see table)
	06  dword	reserved


	|7|6|5|4|3|2|1|0| feature information at offset 5
	 | | | | | | | `--- reserved
	 | | | | | | `---- 0=PC bus, 1=Micro Channel
	 | | | | | `----- Extended BIOS Data Area (EBDA) allocated
	 | | | | `------ wait for external event supported
	 | | | `------- INT 15,4F used (kbd intercept)
	 | | `-------- RTC present
	 | `--------- 2nd 8259 present
	 `---------- DMA channel 3 used by fixed disk BIOS


	- see also  MACHINE IDENT  and  INT 15,C0