Western Digital T13/2132-D Byte, Word at offset n, DWord at word offset n, QWord at word offset n

T13/2132-D Revision 3 June 23, 2010

3.3.10 Byte, word, DWord, and QWord Relationships

Figure 2 illustrates the relationship between bytes, words, DWords, and QWords.

Byte																Byte
													7	6	5	4	3	2	1	0
												MSB								LSB
Word at offset n												Word n
								15 14 13 12 11 10			9	8	7	6	5	4	3	2	1	0
							MSB													LSB
									Byte 2n+1							Byte 2n
DWord at word offset n
							DWord n/2
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10											9	8	7	6	5	4	3	2	1	0
MSB																				LSB
	Byte 2n+3				Byte 2n+2				Byte 2n+1							Byte 2n
		Word n+1										Word n
QWord at word offset n
							QWord n/4
63 ...	56 55 ...		48 47 ...		40 39 ...		32 31 ...		24 23 ...			16 15 ...				8	7		...	0
MSB																				LSB
Byte 2n+7		Byte 2n+6		Byte 2n+5		Byte 2n+4		Byte 2n+3		Byte 2n+2			Byte 2n+1					Byte 2n
	Word n+3				Word n+2				Word n+1							Word n
		DWord n/2+1									DWord n/2

Figure 2 — Byte, word, DWord and QWord relationships

Unless stated or defined otherwise, in a field containing a multi-byte value (e.g., a word, DWord, or QWord), the byte containing the LSB is stored at the lowest offset and the byte containing the MSB is stored at the highest offset.

3.3.11 ATA string convention

ATA strings are sequences of bytes containing ASCII graphic characters in the range of 20h-7Eh. ATA strings shall not contain values in the range of 00h-1Fh or 7Fh-FFh.

10 Working Draft Enhanced Disk Drive - 4 (EDD-4)