of Microprocessors

MICROPROCESSORS 135
perhaps one was that the expense of building a 16-bit system outweighed the
relatively small performance increase these early entries offered.
The earliest high-performance 16-bit microprocessor beyond those
mentioned above was the LSI-ll from Digital EquipP1ent. The microprocessor
was actually designed by Western Digital and was a set of three
large ICs. DEC only offered it on a board with memory and bus interface and
at a relatively high price too. It could run most software written for the
PDP-Il, which is probably the most popular minicomputer ever. Not to be
outdone, Data General came out with their MicroNova, which was available
as a chip as well as a board and executed the Nova minicomputer instruction
set. Its electrical characteristics were highly unorthodox, however. Fairchild
also introduced a Nova-compatible microprocessor called the Microflame,
which was faster and more conventional in its interfacing. None of these
minicomputer emulator microprocessors was ever successful, however. The
seemingly valid approach of solving the software problem by making the
microprocessor execute already written minicomputer software likely failed
because nobody really wanted to run old minicomputer software.
Intel moved next in 1979 and introduced their 8086, which was the
first 16-bit offering from a company with an already successful 8-bit
microprocessor. Compared to some that immediately followed, the 8086 was
not really very sophisticated, but it was faster than earlier offerings and, most
significantly, could run 8080 software after being processed with an
automatic translator program and reassembled. Not much later, Zilog
announced the Z-8000 and Motorola their 68000. These two were incredibly
sophisticated, having large register complements, rich instruction sets, and
very high-speed potential. The 68000 in particular surpassed all but the
biggest minicomputers in its potential power. It actually looked like a 32-bit
computer to a programmer with 16 32-bit general-purpose registers but with
a 16-bit data bus! It could also address up to 16 megabytes of memory directly
without the bank switching (segmentation) the 8086 and Z-8000 required.
Although there was much hope and speculation about a 16-bit version of the
6502 during this time, it never materialized. Much later in 1982, National
Semiconductor tried a new 16-bit design called the 16032. Like the 68000,
it had 32-bit internal architecture but was more oriented toward high-level
language execution and efficient use in time-sharing systems.
As this is being written (late 1984), Intel has had the greatest success
with the 8086 and its variations in terms of both design wins and units sold.
The 68000 is the prestige winner, however, being preferred in systems where
high computation speed and large memory-addressing capacity is important.
The Z-8000 and 16032 are clearly behind with the former suffering from a
lack of promotion and the latter from its late start. True 32-bit versions of all
of these plus new entries from AT&T (the Bellmac-32) and NCR are being
worked on now and can be expected to be generally available in a couple of
years.