AMD 8 manual Data Terminology

Preliminary Information

AMD Athlon™ XP Processor Model 8 Data Sheet 25175H— March 2003

■Invalid and Don’t-Care—In timing diagrams, signal ranges that are invalid or don't-care are filled with a screen pattern.

Data Terminology

The following list defines data terminology:

■Quantities

•A word is two bytes (16 bits)

•A doubleword is four bytes (32 bits)

•A quadword is eight bytes (64 bits)

■Addressing—Memory is addressed as a series of bytes on eight-byte (64-bit) boundaries in which each byte can be separately enabled.

■Abbreviations—The following notation is used for bits and bytes:

•Kilo (K, as in 4-Kbyte page)

•Mega (M, as in 4 Mbits/sec)

•Giga (G, as in 4 Gbytes of memory space)

See Table 31 on page 89 for more abbreviations.

■Little-Endian Convention—The byte with the address xx...xx00 is in the least-significant byte position (little end). In byte diagrams, bit positions are numbered from right to left—the little end is on the right and the big end is on the left. Data structure diagrams in memory show low addresses at the bottom and high addresses at the top. When data items are aligned, bit notation on a 64-bit data bus maps directly to bit notation in 64-bit-wide memory. Because byte addresses increase from right to left, strings appear in reverse order when illustrated.

■Bit Ranges—In text, bit ranges are shown with a dash (for example, bits 9–1). When accompanied by a signal or bus name, the highest and lowest bit numbers are contained in brackets and separated by a colon (for example, AD[31:0]).

■Bit Values—Bits can either be set to 1 or cleared to 0.

■Hexadecimal and Binary Numbers—Unless the context makes interpretation clear, hexadecimal numbers are followed by an h and binary numbers are followed by a b.

88 Appendix B - Conventions and Abbreviations