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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
iii