Intel 80286, 80287 manual Chapter Introduction to

CHAPTER 1

INTRODUCTION TO THE 80286

The 80286 is the most powerful 16-bit processor in the 8086 series of microprocessors, which includes the 8086, the 8088, the 80186, the 80188, and the 80286. It is designed for applications that require very high performance. It is also an excellent choice for sophisticated "high end" applications that will benefit from its advanced architectural features: memory management, protection mechanisms, task management, and virtual memory support. The 80286 provides, on a single VLSI chip, computational and architectural characteristics normally associated with much larger minicomputers.

Sections 1.1, 1.2, and 1.3 of this chapter provide an overview of the 80286 architecture. Because the 80286 represents an extension of the 8086 architecture, some of this overview material may be new and unfamiliar to previous users of the 8086 and similar microprocessors. But the 80286 is also an evolutionary development, with the new architecture superimposed upon the industry standard 8086 in such a way as to affect only the design and programming of operating systems and other such system softwar~. Section 1.4 of this chapter provides a guide to the organization of this manual, suggesting which chapters are relevant to the needs of particular readers.

1.1 GENERAL ATTRIBUTES

The 80286 base architecture has many features in common with the architecture of other members of the 8086 family, such as byte addressable memory, I/O interfacing hardware, interrupt vectoring, and support for both multiprocessing and processor extensions. The entire family has a common set of addressing modes and basic instructions. The 80286 base architecture also includes a number of exten- sions which add to the versatility of the computer.

The 80286 processor can function in two modes of operation (see section 1.2 of this chapter, Modes of Operation). In one of these modes only the base architecture is available to programmers, whereas in the other mode a number of very powerful advanced features have been added, including support for virtual memory, multitasking, and a sophisticated protection mechanism. These advanced features are described in section 1.3 of this chapter.

The 80286 base architecture was designed to support programming in high-level languages, such as Pascal, C or PL/M. The register set and instructions are well suited to compiler-generated code. The addressing modes (see section 2.6.3 in Chapter 2) allow efficient addressing of complex data structures, such as static and dynamic arrays, records, and arrays within records, which are commonly supported by high-level languages. The data types supported by the architecture include, along with bytes and words, high level language constructs such as strings, BCD, and floating point.

The memory architecture of the 80286 was designed to support modular programming techniques. Memory is divided into segments, which may be of arbitrary size, that can be used to contain proce- dures and data structures. Segmentation has several advantages over more conventional linear memory architectures. It supports structured software, since segments can contain meaningful program units and data, and more compact code, since references within a segment can be shorter (and locality of reference usually insures that the next few references will be within the same segment). Segmentation also lends itself to efficient implementation of sophisticated memory management, virtual memory, and memory protection.

In addition, new instructions have been added to the base architecture to give hardware support for procedure invocations, parameter passing, and array bounds checking.

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