Information Technology Reference
In-Depth Information
The goals of the 8086 architectural design were to extend existing 8080 features symmetri-
cally, across the board, and to add processing capabilities not to be found in the 8080. The
added features include 16-bit arithmetic, signed 8- and 16-bit arithmetic (including multiply
and divide), efficient interruptible byte-string operations, and improved bit manipulation.
Significantly, they also include mechanisms for such minicomputer-type operations as reen-
trant code, position-independent code, and dynamically relocatable programs. In addition,
the processor may directly address up to 1 megabyte of memory and has been designed to
support multiple-processor configurations.
The 8086 and 8088 were binary compatible with each other, but not pin compatible. Binary
compatibility means that either microprocessor could execute the same program. Pin incom-
patibility means that you cannot plug the 8086 into the 8088, and vice-versa, and expect the
chips to work. The new 'x86' devices implemented a CISC (Complex Instruction Set Com-
puter design methodology). At the time, many companies were promoting RISC as the fast-
ing processor technology. Intel would eventually win the CISC battle with the release of the
Pentium processor, many years in the future.
At the time, Intel Corporation struggled to supply enough chips to feed the hungry as-
sembly lines of the expanding PC industry. Therefore, to ensure sufficient supply to the per-
sonal computer industry, they subcontracted the fabrication rights of these chips to AMD,
Harris, Hitachi, IBM, Siemens, and possibly others. Amongst Intel and their cohorts, the
8086 line of processors ran at speeds ranging from 4 MHz to 16 MHz.
The Z80 processor, which had beaten the 8080 processor in many ways, led the way for
its new 16-bit processor: the Z8000. Zilog had intended that it was to be compatible with the
previous processor. Unfortunately, the designer decided to redesign the processor, so that it
had an improved architecture, but was not compatible with the Z80. From that time on, Zilog
lost their market share, and this gives an excellent example of compatibility winning over
superior technology. The 8086 design was difficult to work with and was constrained by
compatibility, but it allowed easy migration for system designers.
IBM realized the potential of the PC and microprocessor. Unlike many of their previous
computer systems, they developed their version of the PC using standard components, such
as Intel's 16-bit 8086 microprocessor. They released it as a business computer, which could
run word processors, spread sheets and databases and was named the IBM PC (Figure 1.7). It
has since become the parent of all the PCs ever produced. To increase the production of this
software for the PC they made information on the hardware freely available. This resulted in
many software packages being developed and helped clone manufacturers to copy the origi-
nal design. So the term 'IBM compatible' was born and it quickly became an industry stan-
dard by sheer market dominance.
On previous computers, IBM had written most of their programs for their systems. For
the PC they had a strict time limit, so they first went to Digital Research who was responsi-
ble for developing CP/M, which was proposed as a new standardised operating system for
microprocessors. Unfortunately, for Digital Research, they were unable to reach a final deal
because they could not sign a strict confidentiality agreement. They then went to a small
computer company called Microsoft. For this Bill Gates bought a program called Q-DOS
(often called the Quick and Dirty Operating System) from Seattle Computer Products. Q-
DOS was similar to CP/M, but totally incompatible. Microsoft paid less than $100 000 for
the rights to the software. It was released on the PC as PC-DOS, and Microsoft released their
own version called MS-DOS, which has since become the best selling software in history,
and IBM increased the market for Intel processors, a thousand times over.
