Vol. 3A 2-1

CHAPTER 2

SYSTEM ARCHITECTURE OVERVIEW

IA-32 architecture (beginning with the Intel386 processor family) provides extensive support for operating-system 
and system-development software. This support offers multiple modes of operation, which include:

•

Real mode, protected mode, virtual 8086 mode, and system management mode. These are sometimes 
referred to as legacy modes.

Intel 64 architecture supports almost all the system programming facilities available in IA-32 architecture and 
extends them to a new operating mode (IA-32e mode) that supports a 64-bit programming environment. IA-32e 
mode allows software to operate in one of two sub-modes: 

•

64-bit mode supports 64-bit OS and 64-bit applications

•

Compatibility mode allows most legacy software to run; it co-exists with 64-bit applications under a 64-bit OS.

The IA-32 system-level architecture includes features to assist in the following operations:

•

Memory management

•

Protection of software modules

•

Multitasking

•

Exception and interrupt handling

•

Multiprocessing

•

Cache management

•

Hardware resource and power management

•

Debugging and performance monitoring

This chapter provides a description of each part of this architecture. It also describes the system registers that are 
used to set up and control the processor at the system level and gives a brief overview of the processor’s system-
level (operating system) instructions.
Many features of the system-level architecture are used only by system programmers. However, application 
programmers may need to read this chapter and the following chapters in order to create a reliable and secure 
environment for application programs.
This overview and most subsequent chapters of this book focus on protected-mode operation of the IA-32 architec-
ture. IA-32e mode operation of the Intel 64 architecture, as it differs from protected mode operation, is also 
described. 
All Intel 64 and IA-32 processors enter real-address mode following a power-up or reset (see Chapter 9, “Processor 
Management and Initialization”). Software then initiates the switch from real-address mode to protected mode. If 
IA-32e mode operation is desired, software also initiates a switch from protected mode to IA-32e mode.

2.1 

OVERVIEW OF THE SYSTEM-LEVEL ARCHITECTURE

System-level architecture consists of a set of registers, data structures, and instructions designed to support basic 
system-level operations such as memory management, interrupt and exception handling, task management, and 
control of multiple processors.
Figure 2-1 provides a summary of system registers and data structures that applies to 32-bit modes. System regis-
ters and data structures that apply to IA-32e mode are shown in Figure 2-2.