User's Manual

CHAPTER 1
OVERVIEW OF NUMERIC PROCESSING
The 80287 NPX is a high-performance numerics processing element that extends the 80286 architec-
ture by adding significant numeric capabilities and direct support for floating-point, extended-integer,
and BCD data types. The 80286
CPU with 80287 NPX easily supports powerful and accurate numeric
applications through its implementation of the proposed IEEE 754 Standard for Binary Floating-Point
Arithmetic.
INTRODUCTION TO THE 80287 NUMERIC PROCESSOR EXTENSION
The 80287 Numeric Processor Extension (NPX) is highly compatible with its predecessor, the earlier
Intel 8087
NPX.
The 8087 NPX was designed for use in 8086-family systems. The 8086 was the first microprocessor
family
to partition the processing unit to permit high-performance numeric capabilities. The 8087 NPX
for this processor family implemented a complete numeric processing environment in compliance with
the proposed
IEEE 754 Floating-Point Standard.
With the 80287 Numeric Processor Extension, high-speed numeric computations have been extended
to 80286 high-performance multi-tasking and multi-user systems. Multiple tasks using the numeric
processor extension are afforded the full protection of the 80286 memory management and protection
features.
Figure
1-1 illustrates the relative performance of 8-MHz 8086/8087 and 80286/80287 systems in
executing numerics-oriented applications.
Performance
Table 1-1 compares the execution times of several 80287 instructions with the equivalent operations
executed in software
on an 8-MHz 80286. The software equivalents are highly-optimized assembly-
language procedures from the 80287 emulator.
As indicated in the table, the 80287 NPX provides
about
50 to 100 times the performance of software numeric routines on the 80286 CPU. An 8-MHz
80287 multiplies 32-bit and 64-bit real numbers in about 11.9 and 16.9 microseconds, respectively.
Of
course, the actual performance of the NPX in a given system depends on the characteristics of the
individual application.
Although the performance figures shown
in table 1-1 refer to operations on real (floating-point) numbers,
the 80287 also manipulates fixed-point binary and decimal integers of up to 64 bits or
18 digits, respec-
tively. The 80287 can improve the speed of multiple-precision software algorithms for integer opera-
tions by
10 to 100 times.
Because the 80287
NPX is an extension of the 80286 CPU, no software overhead is incurred in setting
up the
NPX for computation. The 80287 and 80286 processors coordinate their activities in a manner
transparent
to software. Moreover, built-in coordination facilities allow the 80286 CPU to proceed with
other instructions while the 80287
NPX is simultaneously executing numeric instructions. Programs
can exploit this concurrency of execution to further increase system performance and throughput.
1-1