Processor Types and Specifications - Upgrading and Repairing PCs - page 88

For more about the 286 processor, see Chapter 3 of Upgrading and Repairing PCs, 19 th Edition,
available in its entirety on the disc packaged with this topic.
P3 (386) Processors
The third generation represents perhaps the most significant change in processors since the first PC.
The big deal was the migration from processors that handled 16-bit operations to true 32-bit chips.
The third-generation processors were so far ahead of their time that it took fully 10 years before 32-
bit OSs and software became mainstream, and by that time the third-generation chips had become a
memory.
The Intel 80386 (usually abbreviated as 386) caused quite a stir in the PC industry because of the
vastly improved performance it brought to the personal computer. Compared to 8088 and 286
systems, the 386 chip offered greater performance in almost all areas of operation.
The 386 is a full 32-bit processor optimized for high-speed operation and multitasking OSs. Intel
introduced the chip in 1985, but the 386 appeared in the first systems in late 1986 and early 1987.
The Compaq Deskpro 386 and systems made by several other manufacturers introduced the chip;
somewhat later, IBM used the chip in its PS/2 Model 80.
The 386 can execute the real-mode instructions of an 8086 or 8088, but in fewer clock cycles. The
386 was as efficient as the 286 in executing instructions—the average instruction took about 4.5 clock
cycles. In raw performance, therefore, the 286 and 386 actually seemed to be at almost equal clock
rates. The 386 offered greater performance in other ways, mainly because of additional software
capability (modes) and a greatly enhanced memory management unit (MMU). The die for the 386 is
shown in Figure 3.23 .
Figure 3.23. 386 processor die. Photograph used by permission of Intel Corporation.
The 386 can switch to and from protected mode under software control without a system reset—a