Introduction - Computer Busses - page 9

computer systems started to erode from the high-powered end as DEC developed their range
of minicomputers and from the low-powered-end by companies developing computers based
around the newly available 8-bit microprocessors, such as the 6502 and the Z80. IBM's main
contenders, other than DEC, were Apple and Commodore who introduced a new type of
computer - the personal computer (PC). The leading systems, at the time, were the Apple I
and the Commodore PET. These captured the interest of the home user and for the first time
individuals had access to cheap computing power. These flagship computers spawned many
others, such as the Sinclair ZX80/ZX81 (Figure 1.4), the BBC microcomputer, the Sinclair
Spectrum, the Commodore Vic-20 and the classic Apple II (all of which where based on the
6502 or Z80). Most of these computers were aimed at the lower end of the market and were
mainly used for playing games and not for business applications. IBM finally decided, with
the advice of Bill Gates, to use the 8088 for its version of the PC, and not, as they had first
thought, to use the 8080 device. Microsoft also persuaded IBM to introduce the IBM PC with
a minimum of 64 KB RAM, instead of the 16 KB that IBM planned.
Also, in 1972, at XEROX PARC, Alan Kay proposed that XEROX should build a port-
able personal computer, called the Dynabook, which would be the size of an ordinary note-
book; unfortunately, the PARC management did not support it. In future years, companies
such as Toshiba and Compaq would fully exploit the idea. PARC eventually choose to de-
velop the Alto personal computer.
At the time, most people thought that personal computers would be used mainly as games
computers. One of the major innovators in this was Atari, who were founded by Nolan
Bushnell. They produced the first ever commercial game based on tennis, named Pong. By
today's standards, Pong used simple graphics. It had just two paddle lines, which could be
moved left and right, and a square ball, which moved back and forward between the paddles.
Atari and other companies would release many other classic games, such as Space Invaders,
Asteroids and Frogger.
At the time, Texas Instruments was well advanced in microprocessor development and
introduced the TMS1000 one-chip microcomputer. It had 1 KB ROM, 32 bytes of RAM with
a simple 4-bit processor. In the following year (1973), Intel filed a patent application for a
memory system for a multichip digital computer.
In 1973, the model for future computer systems occurred at Xerox's PARC, when the
Alto workstation was demonstrated with a bit mapped screen (showing the Cookie Monster,
from Sesame Street). The following year, at Xerox, Bob Metcalfe demonstrated the Ethernet
networking technology, which was destined to become the standard local area networking
technique. It was far from perfect, as computers contended with each other for access to the
network, but it was cheap and simple, and it worked relatively well.
Also in 1973, before the widespread acceptance of PC-DOS, the future for personal com-
puter operating systems looked to be CP/M (Control Program/Monitor), which was written
by Gary Kildall of Digital Research. One of his first applications of CP/M was on the Intel
8008, and then on the Intel 8080. At the time, computers based on the 8008 started to appear,
such as the Scelbi-8H, which cost $565 and had 1 KB of memory.
IBM was also innovating at the time, creating a cheap floppy disk drive. They also pro-
duced the IBM 3340 hard disk unit (a Winchester disk) which had a recording head which
sat on a cushion of air, 18 millionths of an inch above the platter. The disk was made with
four platters, each was 8-inches in diameter, giving a total capacity of 70 MB.
A year later (1974), at IBM, John Cocke produced a high-reliability, low-maintenance
computer called the ServiceFree. It was one of the first computers in the world to use RISC
technology and it operated at the unbelievable speed of 80 MIPS. Most computers at the time
were measured in a small fraction of a MIP, and, at the time, were over 50 times faster than