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CHAPTER 1
SYSTEM OVERVIEW
The 80386 is a new 32-bit microprocessor that forms the basis for a high-performance
32-bit system. The 80386 incorporates multitasking support, memory management, pipelined
architecture, address translation caches, and a high-speed bus interface all on one chip. The
integration of these features speeds the execution of instructions and reduces overall chip
count for a system. Paging and dynamic data bus sizing can each be invoked selectively,
making the 80386 suitable for a wide variety of system designs and user applications.
While the 80386 represents a significant improvement over previous generations of micro-
processors, substantial ties to the earlier processors are preserved. Software compatibility at
the object-code level is provided, so that an existing investment in 8086 and 80286 software
can be maintained. New software can be built upon existing routines, reducing the time to
market for new products. Hardware compatibility is preserved through the dynamic bus-
sizing feature.
The major components of an 80386 system and their functions are shown in Figure 1-1.
Table 1-1 describes these components.
1.1 MICROPROCESSOR
The 80386 provides unprecedented performance. At 20 MHz, the 80386 is capable of
executing at sustained rates of over five million instructions per second, a speed comparable
to that of most super minicomputers. This achievement is made possible through a state-of-
the-art design that includes a pipelined internal architecture, address translation caches, and
a high-performance bus.
The 80386 features 32-bit wide internal and external data paths and eight general-purpose
32-bit registers. The instruction set offers 8-, 16-, and 32-bit data types, and the processor
outputs 32-bit physical addresses directly, for a physical memory capacity of four gigabytes.
Table 1-1. 80386 System Components
Component
Description
80386 Microprocessor
32-bit high-performance microprocessor with on-
chip memory management and protection
80287 or 80387 Numeric Coprocessor
Performs numeric instruction in parallel with
80386; expands instruction set
82380 Integrated System Peripheral
Provides 32-bit high-speed direct memory access,
interrupt control, and interval timers
82385 Cache Controller
Provides cache directory and management logic
82384 Clock Generator
Generates system clock and RESET signal
8259A Programmable Interrupt Controller
Provides interrupt control and management
82258 Advanced DMA
Performs direct memory controller access (DMA)
1-1
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