Introduction - Computer Busses - page 20

Intel's first of many failed attempts at the x86 chip integration game.
The new instructions and fault tolerance additions were logical evolutions of the 8086
and 8088. Intel added instructions that made programming much more convenient for low-
level (assembly language) programmers. Intel also added some fault tolerance protection.
The original 8086 and 8088 would hang when they encountered an invalid computer instruc-
tion, whereas the 80186 and 80188 added the ability to trap this condition and attempt a re-
covery method.
Intel integrated this processor with many of the peripheral chips already employed in the
IBM PC. The 80186/80188 integrated interrupt controllers, interval timers, DMA controllers,
clock generators, and other core support logic. In many ways, the device was produced a
decade ahead of its time. Unfortunately, this device did not catch on with many hardware
manufacturers; this spelled the end of Intel's first attempt at CPU integration. However, this
device has enjoyed a tremendous success in the world of embedded processors. If you look
on your high performance disk driver or disk controller, you might still see an 80186 being
used.
Eventually, many embedded processor vendors began manufacturing these devices as a
second source to Intel, or in clones of their own. Between the various vendors, the
80186/80188 was available in speeds ranging from 6 MHz to 40 MHz.

1.5 80286

In 1982, Intel introduced the 80286. For the first time, Intel did not simultaneously introduce
an 8-bit bus version of this processor (such as the 80288). The 80286 introduced some sig-
nificant microprocessor extensions. Intel continued to extend the instruction set; more sig-
nificantly, Intel added four more address lines and a new operating mode called 'protected
mode'. The 8086, 8088, 80186 and 80188 all contained 20 address lines, giving these proc-
essors one megabyte of addressibility (2 20 = 1 MB). The 80286, with its 24 address lines,
gives 16 megabytes of addressibility (2 24 = 16 MB).
For the most part, the new instructions of the 80286 were introduced to support the new
protected mode. Real mode was still limited to the one megabyte program addressing of the
8086, et al. Essentially, a program could not take advantage of the 16-megabyte address
space without using protected mode. Unfortunately, protected mode could not run real-mode
(DOS) programs. These limitations thwarted attempts to adopt the 80286 programming ex-
tensions for mainstream consumer use.
During the reign of the 80286, the first 'chipsets' were introduced. These were nothing
more than a set of devices that replaced dozens of other peripheral devices, while maintain-
ing identical functionality. Chips and Technologies became one of the first popular chipset
companies.
IBM was spurred by the huge success of the IBM PC and decided to use the 80286 in
their next generation computer, the IBM PC-AT. However, the PC-AT was not introduced
until 1985, which was three years after introduction of the 80286. IBM, it seems, were actu-
ally frightened by the thought of the 32-bit processors as they allowed PCs to challenge their
thriving minicomputer market. A new threat to the PC emerged from Apple, who used the
Motorola 68000 processor, with an excellent operating system, to produce the Apple Mac
computer. It had a full graphical user interface, which was based around windows and icon,
and had a mouse pointer to allow users to easily move around the computer system.