User's Manual

PREFACE
AN INTRODUCTION TO THE 80286
This supplement describes the 80287 Numeric Processor Extension (NPX) for the 80286 microproces-
sor. Below
is a brief overview of 80286 concepts, along with some of the nomenclature used throughout
this and other Intel publications.
The 80286 Microsystem
The 80286 is a new VLSI microprocessor system with exceptional capabilities for supporting large-
system applications. Based
on a new-generation CPU (the Intel 80286), this powerful microsystem is
designed to support multiuser reprogrammable and real-time multitasking applications. Its dedicated
system support circuits simplify system hardware; sophisticated hardware and software tools reduce
both the time and the cost of product development.
The 80286
is a virtual-memory microprocessor with on-chip memory management and protection. The
80286 microsystem offers a total-solution approach, enabling you to develop high-speed, interactive,
multiuser,
multitasking-and multiprocessor-systems more rapidly and at higher performance than
ever before.
• Reliability and system up-time are becoming increasingly important in all applications. Information
must be protected from misuse or accidental
loss. The 80286 includes a sophisticated and flexible
four-level protection mechanism that isolates layers of operating system programs from application
programs to maintain a high degree of system integrity.
• The 80286 provides 16 megabytes of physical address space to support today's application require-
ments. This large physical memory enables the 80286 to keep many large programs and data struc-
tures simultaneously in memory for high-speed access.
• For applications with dynamically changing memory requirements, such as multiuser business
systems, the 80286
CPU provides on-chip memory management and virtual memory support. On
an 80286-based system, each user can have up to a gigabyte (2
30
bytes) of virtual-address space.
This large address space virtually eliminates restrictions
on the number or size of programs that
may be part of the system.
• Large multiuser or real-time multitasking systems are easily supported by the 80286. High~perform
ance features, such as a very high-speed task switch, fast interrupt-response time, inter-task protec-
tion, and a quick and direct operating system interface, make the 80286 highly suited
to multiuser/
multitasking applications.
• The 80286 has two operating modes: Real-Address mode and Protected-Address mode. In Real-
Address mode, the 80286
is fully compatible with the 8086, 8088, 80186, and 80188 microproces-
sors; all of the extensive libraries of 8086 and 8088 software execute four to
six times faster on the
80286, without any modification.
• In Protected-Address mode, the advanced memory management and protection features of the 80286
become available, without any. reduction
in performance. Upgrading 8086 and 8088 application
programs to use these
new memory management and protection features usually requires only
reassembly or recompilation (some programs may require minor modification). This compatibility
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