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T13/2132-D Revision 3 June 23, 2010
10 Working Draft Enhanced Disk Drive - 4 (EDD-4)
3.3.10 Byte, word, DWord, and QWord Relationships
Figure 2 illustrates the relationship between bytes, words, DWords, and QWords.
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.
QWord n/4
DWord n/2
Word n
Byte
76543210
Byte
76543210
Word at offset n
15 14 13 12 11 10 9 8
76543210
DWord at word offset n
15 14 13 12 11 10 9 823 22 21 20 19 18 17 1631 30 29 28 27 26 25 24
Byte 2nByte 2n+1
MSB LSB
Byte 2nByte 2n+1Byte 2n+2Byte 2n+3
15 8 7 0
QWord at word offset n
31 24 23 1647 40 39 3263 56 55 48
Byte 2n
Word nWord n+1
... ... ... ... ... ... ... ...
MSB
MSB
LSB
LSB
DWord n/2DWord n/2+1
Word nWord n+1Word n+2Word n+3
MSB LSB
Byte 2n+1Byte 2n+2Byte 2n+3Byte 2n+4Byte 2n+5Byte 2n+6Byte 2n+7