User Guide

xxii Preface
AMD64 Technology 24592—Rev. 3.15—November 2009
long mode
An operating mode unique to the AMD64 architecture. A processor implementation of the
AMD64 architecture can run in either long mode or legacy mode. Long mode has two submodes,
64-bit mode and compatibility mode.
lsb
Least-significant bit.
LSB
Least-significant byte.
main memory
Physical memory, such as RAM and ROM (but not cache memory) that is installed in a particular
computer system.
mask
(1) A control bit that prevents the occurrence of a floating-point exception from invoking an
exception-handling routine. (2) A field of bits used for a control purpose.
MBZ
Must be zero. If software attempts to set an MBZ bit to 1, a general-protection exception (#GP)
occurs.
memory
Unless otherwise specified, main memory.
ModRM
A byte following an instruction opcode that specifies address calculation based on mode (Mod),
register (R), and memory (M) variables.
moffset
A 16, 32, or 64-bit offset that specifies a memory operand directly, without using a ModRM or SIB
byte.
msb
Most-significant bit.
MSB
Most-significant byte.
multimedia instructions
A combination of 128-bit media instructions and 64-bit media instructions.
octword
Same as double quadword.