Intel 80286 manual Introduction to the 80287 Numeric Processor Extension, Performance

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.

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