User Guide

2 Overview of the AMD64 Architecture
AMD64 Technology 24592—Rev. 3.15—November 2009
Figure 1-1. Application-Programming Register Set
Table 1-1. Operating Modes
Operating Mode
Operating
System Required
Application
Recompile
Required
Defaults
Register
Extensions
Typical
Address
Size
(bits)
Operand
Size
(bits)
GPR
Width (bits)
Long
Mode
64-Bit
Mode
64-bit OS
yes 64
32
yes 64
Compatibility
Mode
no
32
no
32
16 16 16
Legacy
Mode
Protected
Mode
Legacy 32-bit OS
no
32 32
no
32
16 16
Virtual-8086
Mode
16 16 16
Real
Mode
Legacy 16-bit OS
513-101.eps
Flags Register
Instruction Pointer
General-Purpose
Registers (GPRs)
128-Bit Media
Registers
64-Bit Media and
Floating-Point Registers
Legacy x86 registers, supported in all modes Application-programming registers also include the
128-bit media control-and-status register and the
x87 tag-word, control-word, and status-word registers
63 0 63 0
63 0
127 0
63 0
Register extensions, supported in 64-bit mode
RAX
RBX
RCX
RDX
RBP
RSI
RDI
RSP
R8
R9
R10
R11
R12
R13
R14
R15
MMX0/FPR0
MMX1/FPR1
MMX2/FPR2
MMX3/FPR3
MMX4/FPR4
MMX5/FPR5
MMX6/FPR6
MMX7/FPR7
XMM0
XMM1
XMM2
XMM3
XMM4
XMM5
XMM6
XMM7
XMM8
XMM9
XMM10
XMM11
XMM12
XMM13
XMM14
XMM15
0 RFLAGS
RIP
EFLAGS
EIP