Offset Hex 	Offset Dec 	Field Size 	Function

00h
	0 	1 byte 	RTC seconds.  Contains the seconds value of current time
01h 	1 	1 byte 	RTC seconds alarm.  Contains the seconds value for the RTC alarm
02h 	2 	1 byte 	RTC minutes.  Contains the minutes value of the current time
03h 	3 	1 byte 	RTC minutes alarm.  Contains the minutes value for the RTC alarm
04h 	4 	1 byte 	RTC hours.  Contains the hours value of the current time
05h 	5 	1 byte 	RTC hours alarm.  Contains the hours value for the RTC alarm
06h 	6 	1 byte 	RTC day of week.  Contains the current day of the week
07h 	7 	1 byte 	RTC date day.  Contains day value of current date
08h 	8 	1 byte 	RTC date month.  Contains the month value of current date
09h 	9 	1 byte 	RTC date year.  Contains the year value of current date
0Ah 	10 	1 byte 	Status Register A 
  	  	  	Bit 7 = Update in progress (0 = Date and time can be read, 1 = Time update in progress)
  	  	  	Bits 6-4 = Time frequency divider (010 = 32.768KHz
  	  	  	Bits 3-0 = Rate selection frequency (0110 = 1.024KHz square wave frequency)
0Bh 	11 	1 byte 	Status Register B
  	  	  	Bit 7 = Clock update cycle (0 = Update normally, 1 = Abort update in progress)
  	  	  	Bit 6 = Periodic interrupt (0 = Disable interrupt (default), 1 = Enable interrupt)
  	  	  	Bit 5 = Alarm interrupt (0 = Disable interrupt (default), 1 = Enable interrupt)
  	  	  	Bit 4 = Update ended interrupt (0 = Disable interrupt (default), 1 = Enable interrupt)
  	  	  	Bit 3 = Status register A square wave frequency (0 = Disable square wave (default), 1 = Enable square wave)
  	  	  	Bit 2 = 24 hour clock (0 = 24 hour mode (default), 1 = 12 hour mode)
  	  	  	Bit 1 = Daylight savings time (0 = Disable daylight savings (default), 1 = Enable daylight savings)
0Ch 	12 	1 byte 	Status Register C - Read only flags indicating system status conditions
  	  	  	Bit 7 = IRQF flag
  	  	  	Bit 6 = PF flag
  	  	  	Bit 5 = AF flag
  	  	  	Bit 4 UF flag
  	  	  	Bits 3-0 = Reserved
0Dh 	13 	1 byte 	Status Register D - Valid CMOS RAM flag on bit 7 (battery condition flag)
  	  	  	Bit 7 = Valid CMOS RAM flag (0 = CMOS battery dead, 1 = CMOS battery power good)
  	  	  	Bit 6-0 = Reserved
0Eh 	14 	1 byte 	Diagnostic Status
  	  	  	Bit 7 = Real time clock power status (0 = CMOS has not lost power, 1 = CMOS has lost power)
  	  	  	Bit 6 = CMOS checksum status (0 = Checksum is good, 1 = Checksum is bad)
  	  	  	Bit 5 = POST configuration information status (0 = Configuration information is valid, 1 = Configuration information in invalid)
  	  	  	Bit 4 = Memory size compare during POST (0 = POST memory equals configuration, 1 = POST memory not equal to configuration)
  	  	  	Bit 3 = Fixed disk/adapter initialization (0 = Initialization good, 1 = Initialization bad)
  	  	  	Bit 2 = CMOS time status indicator (0 = Time is valid, 1 = Time is invalid)
  	  	  	Bit 1-0 = Reserved
0Fh 	15 	1 byte 	CMOS Shutdown Status
  	  	  	00h = Power on or soft reset
  	  	  	01h = Memory size pass
  	  	  	02h = Memory test pass
  	  	  	03h = Memory test fail
  	  	  	04h = POST complete; boot system
  	  	  	05h = JMP double word pointer with EOI
  	  	  	06h = Protected mode tests pass
  	  	  	07h = protected mode tests fail
  	  	  	08h = Memory size fail
  	  	  	09h = Int 15h block move
  	  	  	0Ah = JMP double word pointer without EOI
  	  	  	0Bh = Used by 80386
10h 	16 	1 byte 	Floppy Disk Drive Types
  	  	  	Bits 7-4 = Drive 0 type
  	  	  	Bits 3-0 = Drive 1 type
  	  	  	0000 = None
  	  	  	0001 = 360KB
  	  	  	0010 = 1.2MB
  	  	  	0011 = 720KB
  	  	  	0100 = 1.44MB
11h 	17 	1 byte 	System Configuration Settings
  	  	  	Bit 7 = Mouse support disable/enable
  	  	  	Bit 6 = Memory test above 1MB disable/enable
  	  	  	Bit 5 = Memory test tick sound disable/enable
  	  	  	Bit 4 = Memory parity error check disable/enable
  	  	  	Bit 3 = Setup utility trigger display disable/enable
  	  	  	Bit 2 = Hard disk type 47 RAM area (0:300h or upper 1KB of DOS area)
  	  	  	Bit 1 = Wait for <F1> if any error message disable/enable
  	  	  	Bit 0 = System boot up with Numlock (off/on)
12h 	18 	1 byte 	Hard Disk Types
  	  	  	Bits 7-4 = Hard disk 0 type
  	  	  	Bits 3-0 = Hard disk 1 type
  	  	  	0000 = No drive installed
  	  	  	0001 = Type 1 installed
  	  	  	1110 = Type 14 installed
  	  	  	1111 = Type 16-47 (defined later in 19h)
13h 	19 	1 byte 	Typematic Parameters
  	  	  	Bit 7 = typematic rate programming disable/enabled
  	  	  	Bit 6-5 = typematic rate delay
  	  	  	Bit 4-2 = Typematic rate
14h 	20 	1 byte 	Installed Equipment
  	  	  	Bits 7-6 = Number of floppy disks (00 = 1 floppy disk, 01 = 2 floppy disks)
  	  	  	Bits 5-4 = Primary display (00 = Use display adapter BIOS, 01 = CGA 40 column, 10 = CGA 80 column, 11 = Monochrome Display Adapter)
  	  	  	Bit 3 = Display adapter installed/not installed
  	  	  	Bit 2 = Keyboard installed/not installed
  	  	  	Bit 1 = math coprocessor installed/not installed
  	  	  	Bit 0 = Always set to 1
15h 	21 	1 byte 	Base Memory Low Order Byte - Least significant byte
16h 	22 	1 byte 	Base Memory High Order Byte - Most significant byte
17h 	23 	1 byte 	Extended Memory Low Order Byte - Least significant byte
18h 	24 	1 byte 	Extended Memory High Order Byte - Most significant byte
19h 	25 	1 byte 	Hard Disk 0 Extended Type - (10h to 2Eh = Type 16 to 46 respectively)
1Ah 	26 	1 byte 	Hard Disk 1 Extended Type - (10h to 2Eh = Type 16 to 46 respectively)
1Bh 	27 	1 byte 	User Defined Drive C: - Number of cylinders least significant byte
1Ch 	28 	1 byte 	User Defined Drive C: - Number of cylinders most significant byte
1Dh 	29 	1 byte 	User Defined Drive C: - Number of heads
1Eh 	30 	1 byte 	User Defined Drive C: - Write precomp cylinder least significant byte
1Fh 	31 	1 byte 	User Defined Drive C: - Write precomp cylinder most significant byte
20h 	32 	1 byte 	User Defined Drive C: - Control byte
21h 	33 	1 byte 	User Defined Drive C: - Landing zone least significant byte
22h 	34 	1 byte 	User Defined Drive C: - Landing zone most significant byte
23h 	35 	1 byte 	User Defined Drive C: - Number of sectors
24h 	36 	1 byte 	User Defined Drive D: - Number of cylinders least significant byte
25h 	37 	1 byte 	User defined Drive D: - Number of cylinders most significant byte
26h 	38 	1 byte 	User Defined Drive D: - Number of heads
27h 	39 	1 byte 	User Defined Drive D: - Write precomp cylinder least significant byte
28h 	40 	1 byte 	User Defined Drive D: - Write precomp cylinder most significant byte
29h 	41 	1 byte 	User Defined Drive D: - Control byte
2Ah 	42 	1 byte 	User Defined Drive D: - Landing zone least significant byte
2Bh 	43 	1 byte 	User Defined Drive D: - Landing zone most significant byte
2Ch 	44 	1 byte 	User Defined Drive D: - Number of sectors
2Dh 	45 	1 byte 	System Operational Flags
  	  	  	Bit 7 = Weitek processor present/absent
  	  	  	Bit 6 = Floppy drive seek at boot enable/disable
  	  	  	Bit 5 = System boot sequence
  	  	  	Bit 4 = System boot CPU speed high/low
  	  	  	Bit 3 = External cache enable/disable
  	  	  	Bit 2 = Internal cache enable/disable
  	  	  	Bit 1 = Fast gate A20 operation enable/disable
  	  	  	Bit 0 = Turbo switch function enable/disable
2Eh 	46 	1 byte 	CMOS Checksum High Order Byte - Most significant byte
2Fh 	47 	1 byte 	CMOS Checksum Low Order Byte - Least significant byte
30h 	48 	1 byte 	Actual Extended Memory Low Order Byte - Least significant byte
31h 	49 	1 byte 	Actual Extended Memory High Order Byte - Most significant byte
32h 	50 	1 byte 	Century Date BCD - Value for century of current date
33h 	51 	1 byte 	POST Information Flags
  	  	  	Bit 7 = BIOS length (64KB/128KB)
  	  	  	Bit 6-1 = reserved
  	  	  	Bit 0 = POST cache test passed/failed
34h 	52 	1 byte 	BIOS and Shadow Option Flags
  	  	  	Bit 7 = Boot sector virus protection disabled/enabled
  	  	  	Bit 6 = Password checking option disabled/enabled
  	  	  	Bit 5 = Adapter ROM shadow C800h (16KB) disabled/enabled
  	  	  	Bit 4 = Adapter ROM shadow CC00h (16KB) disabled/enabled
  	  	  	Bit 3 = Adapter ROM shadow D000h (16KB) disabled/enabled
  	  	  	Bit 2 = Adapter ROM shadow D400h (16KB) disabled/enabled
  	  	  	Bit 1 = Adapter ROM shadow D800h (16KB) disabled/enabled
  	  	  	Bit 0 = Adapter ROM shadow DC00h (16KB) disabled/enabled
35h 	53 	1 byte 	BIOS and Shadow Option Flags
  	  	  	Bit 7 = Adapter ROM shadow E000h (16KB) disabled/enabled
  	  	  	Bit 6 = Adapter ROM shadow E400h (16KB) disabled/enabled
  	  	  	Bit 5 = Adapter ROM shadow E800h (16KB) disabled/enabled
  	  	  	Bit 4 = Adapter ROM shadow EC00h (16KB) disabled/enabled
  	  	  	Bit 3 = System ROM shadow F000h (16KB) disabled/enabled
  	  	  	Bit 2 = Video ROM shadow C000h (16KB) disabled/enabled
  	  	  	Bit 1 = Video ROM shadow C400h (16KB) disabled/enabled
  	  	  	Bit 0 = Numeric processor test disabled/enabled
36h 	54 	1 byte 	Chipset Specific Information
37h 	55 	1 byte 	Password Seed and Color Option
  	  	  	Bit 7-4 = Password seed (do not change)
  	  	  	Bit 3-0 = Setup screen color palette
  	  	  	07h = White on black
  	  	  	70h = Black on white
  	  	  	17h = White on blue
  	  	  	20h = Black on green
  	  	  	30h = Black on turquoise
  	  	  	47h = White on red
  	  	  	57h = White on magenta
  	  	  	60h = Black on brown
38h-3dh 	56-61 	6 bytes 	Encrypted Password - (do not change)
3Eh 	62 	1 byte 	Extended CMOS Checksum - Most significant byte
3Fh 	63 	1 byte 	Extended CMOS Checksum - Least significant byte
40h 	64 	1 byte 	Model Number Byte
41h 	65 	1 byte 	1st Serial Number Byte
42h 	66 	1 byte 	2nd Serial Number Byte
43h 	67 	1 byte 	3rd Serial Number Byte
44h 	68 	1 byte 	4th Serial Number Byte
45h 	69 	1 byte 	5th Serial Number Byte
46h 	70 	1 byte 	6th Serial Number Byte
47h 	71 	1 byte 	CRC Byte
48h 	72 	1 byte 	Century Byte
49h 	73 	1 byte 	Date Alarm
4Ah 	74 	1 byte 	Extended Control Register 4A
4Bh 	75 	1 byte 	Extended Control register 4B
4Ch 	76 	1 byte 	Reserved
4Dh 	77 	1 byte 	Reserved
4Eh 	78 	1 byte 	Real Time Clock - Address 2
4Fh 	79 	1 byte 	Real Time Clock - Address 3
50h 	80 	1 byte 	Extended RAM Address - Least significant byte
51h 	81 	1 byte 	Extended RAM Address - Most significant byte
52h 	82 	1 byte 	Reserved
53h 	83 	1 byte 	Extended RAM Data Port
54h 	84 	1 byte 	Reserved
55h 	85 	1 byte 	Reserved
56h 	86 	1 byte 	Reserved
57h 	87 	1 byte 	Reserved
58h 	88 	1 byte 	Reserved
59h 	89 	1 byte 	Reserved
5Ah 	90 	1 byte 	Reserved
5Bh 	91 	1 byte 	Reserved
5Ch 	92 	1 byte 	Reserved
5Dh 	93 	1 byte 	Reserved
