Intel architecture ia-32 Manual Do Utilizador
Vol. 3A 15-1
CHAPTER 15
8086 EMULATION
IA-32 processors (beginning with the Intel386 processor) provide two ways to execute new or
legacy programs that are assembled and/or compiled to run on an Intel 8086 processor:
legacy programs that are assembled and/or compiled to run on an Intel 8086 processor:
•
Real-address mode.
•
Virtual-8086 mode.
Figure 2-3 shows the relationship of these operating modes to protected mode and system
management mode (SMM).
management mode (SMM).
When the processor is powered up or reset, it is placed in the real-address mode. This operating
mode almost exactly duplicates the execution environment of the Intel 8086 processor, with
some extensions. Virtually any program assembled and/or compiled to run on an Intel 8086
processor will run on an IA-32 processor in this mode.
mode almost exactly duplicates the execution environment of the Intel 8086 processor, with
some extensions. Virtually any program assembled and/or compiled to run on an Intel 8086
processor will run on an IA-32 processor in this mode.
When running in protected mode, the processor can be switched to virtual-8086 mode to run
8086 programs. This mode also duplicates the execution environment of the Intel 8086
processor, with extensions. In virtual-8086 mode, an 8086 program runs as a separate protected-
mode task. Legacy 8086 programs are thus able to run under an operating system (such as
Microsoft Windows*) that takes advantage of protected mode and to use protected-mode facil-
ities, such as the protected-mode interrupt- and exception-handling facilities. Protected-mode
multitasking permits multiple virtual-8086 mode tasks (with each task running a separate 8086
program) to be run on the processor along with other non-virtual-8086 mode tasks.
8086 programs. This mode also duplicates the execution environment of the Intel 8086
processor, with extensions. In virtual-8086 mode, an 8086 program runs as a separate protected-
mode task. Legacy 8086 programs are thus able to run under an operating system (such as
Microsoft Windows*) that takes advantage of protected mode and to use protected-mode facil-
ities, such as the protected-mode interrupt- and exception-handling facilities. Protected-mode
multitasking permits multiple virtual-8086 mode tasks (with each task running a separate 8086
program) to be run on the processor along with other non-virtual-8086 mode tasks.
This section describes both the basic real-address mode execution environment and the virtual-
8086-mode execution environment, available on the IA-32 processors beginning with the
Intel386 processor.
8086-mode execution environment, available on the IA-32 processors beginning with the
Intel386 processor.
15.1
REAL-ADDRESS MODE
The IA-32 architecture’s real-address mode runs programs written for the Intel 8086, Intel 8088,
Intel 80186, and Intel 80188 processors, or for the real-address mode of the Intel 286, Intel386,
Intel486, Pentium, P6 family, Pentium 4, and Intel Xeon processors.
Intel 80186, and Intel 80188 processors, or for the real-address mode of the Intel 286, Intel386,
Intel486, Pentium, P6 family, Pentium 4, and Intel Xeon processors.
The execution environment of the processor in real-address mode is designed to duplicate the
execution environment of the Intel 8086 processor. To an 8086 program, a processor operating
in real-address mode behaves like a high-speed 8086 processor. The principal features of this
architecture are defined in Chapter 3, “Basic Execution Environment”, of the IA-32 Intel®
Architecture Software Developer’s Manual, Volume 1.
execution environment of the Intel 8086 processor. To an 8086 program, a processor operating
in real-address mode behaves like a high-speed 8086 processor. The principal features of this
architecture are defined in Chapter 3, “Basic Execution Environment”, of the IA-32 Intel®
Architecture Software Developer’s Manual, Volume 1.