AT Attachment-3 Interface (ATA-3), Revision 6

(informative)

1. B.1 Definitions and background information

The following abbreviations are used in this annex:

• 528 MB is used to describe a drive device that has 1 032 192 sectors or 528 482 304 bytes.
• 8 GB is used to describe a drivedevice that has 16 515 072 sectors or 8 455 716 864 bytes.

The original IBM PC BIOS (Basic Input/Output System) imposed several restrictions on the support of disk drivesdevices, and these have been incorporated into many higher level software products. One such restriction limits the capacity of a hard disk drivedevice. Most BIOS software cannot support a disk drive device with more than 1,024 cylinders, 16 heads and 63 sectors per track. The maximum addressable capacity of an ATA disk drive a device under this scheme is 528 MB.

There is growing support of auto-configuration for disk drives devices on PC systems. The auto-configuration capability usually resides in the BIOS and uses the IDENTIFY DEVICE command data to configure an ATA disk drivea device.

This annex defines rules for the IDENTIFY DEVICE data of all capacity ATA disk drives devices and allows BIOS support of ATA drives devices up to 8 GB using Cylinder/Head/Sector (CHS) addressing.

This specification defines information that newer BIOSs and system software can use to determine the true size of a disk drive device and access the full capacity of the drivedevice.

1. B.2 Cylinder, head and sector addressing

BIOSs and other software that operate an ATA disk drive a device in CHS (Cylinder, Head and Sector) addressing mode use IDENTIFY DEVICE data words 1, 3, 6 and words 53-58 to ascertain the appropriate translation mode to use and determine the capacity of an ATA disk drivea device.

Maximum compatibility is achieved if the following rules are obeyed. These rules limit the values placed into words 1, 3, 6, and 53-58. The rules specified here for CHS addressing apply to drives devices up to 8 GB.

1. B.2.1 Word 1

For drivesdevices less than or equal to 528 MB, IDENTIFY DEVICE data word 1 (Default Cylinders) does not specify a value greater than 1 024.

If a drivedevice is greater than 528 MB but less than or equal to 8 GB, the maximum value that is placed into this word is determined by the value in Word 3 as shown in table B.1.

 

Table B.1 - Word 1 value

	Value in Word 3		Maximum value in Word 1
	1	1h	65 535	FFFFh
	2	2h	65 535	FFFFh
	3	3h	65 535	FFFFh
	4	4h	65 535	FFFFh
	5	5h	32 767	7FFFh
	6	6h	32 767	7FFFh
	7	7h	32 767	7FFFh
	8	8h	32 767	7FFFh
	9	9h	16 383	3FFFh
	10	Ah	16 383	3FFFh
	11	Bh	16 383	3FFFh
	12	Ch	16 383	3FFFh
	13	Dh	16 383	3FFFh
	14	Eh	16 383	3FFFh
	15	Fh	16 383	3FFFh
	16	10h	16 383	3FFFh

The value in this word does not change.

2. B.2.2 Word 3

IDENTIFY DEVICE data word 3 (Default Heads) does not specify a value greater than 16.

The value in this word does not change.

3. B.2.3 Word 6

For drives of 8 GB or less, IDENTIFY DEVICE data word 6 (Default Sectors) does not specify a value greater than 63.

The value in this word does not change.

4. B.2.4 Use of words 53 through 58

Devices that are over 528 MB implement words 53-58. Drives Devices not over 528 MB may also implement these words. These words define the addressing for all sectors accessible in CHS mode.

5. B.2.5 Word 53

IDENTIFY DEVICE data word 53 bit 0 is set to one at all times that the drivedevice is in a valid translation mode. Some drives devices may have translation modes that cannot be supported. An attempt to put a drive device into one of these unsupported modes causes word 53 bit 0 to be cleared to zero with words 54-58 cleared to zero until a valid translation mode is established.

6. B.2.6 Word 54

IDENTIFY DEVICE data word 54 (Current Cylinders) specifies the number of full logical cylinders that can be accessed in the current translation mode. If an INITIALIZE DEVICE PARAMETERS command has not been executed, the contents of this word is the same as word 1. If an INITIALIZE DEVICE PARAMETERS command has been executed, this word is the integer result of dividing the total number of user sectors (this value may be in words 60-61) by the number of sectors per logical cylinder ( [word55] x [word56] ), but is not a value greater than 65 535.

 

7. B.2.7 Word 55

IDENTIFY DEVICE data word 55 (Current Heads) is the number of heads specified by the last INITIALIZE DEVICE PARAMETERS command. This word contains a value of between 1 and 16. If an INITIALIZE DEVICE PARAMETERS command has not been executed, the contents of this word are the same as word 3.

8. B.2.8 Word 56

IDENTIFY DEVICE data word 56 (Current Sectors) is the number of sectors specified by the last INITIALIZE DEVICE PARAMETERS command. This word may contain a value of between 1 and 255. If an INITIALIZE DEVICE PARAMETERS command has not been executed, the contents of this word are the same as word 6.

9. B.2.9 Words 57-58

IDENTIFY DEVICE data words 57-58 contain a 32-bit value that is equal to [word54] x [word55] x [word56]. Words 57-58 are less than or equal to the value in words 60-61 at all times.

2. B.3 Orphan sectors