Many discoveries and inventions have directly and indirectly contributed to the development of the personal computer. Examining
a few important developmental landmarks can help bring the entire picture into focus.
Personal Computing History
A modern digital computer is largely a collection of electronic switches. These switches are used to represent, as well
as to control, the routing of data elements called binary digits (or bits). Because of the on or off
nature of the binary information and signal routing used by the computer, an efficient electronic switch was required. The
first electronic computers used vacuum tubes as switches, and although the tubes worked, they had many problems.
The tube was inefficient as a switch. It consumed a great deal of electrical power and gave off enormous heat--a significant
problem in the earlier systems. Primarily because of the heat they generated, tubes were notoriously unreliable--one failed
every couple hours or so in the larger systems.
The invention of the transistor, or semiconductor, was one of the most important developments leading to the personal computer
revolution. The transistor was invented in 1948 by Bell Laboratories engineers John Bardeen, Walter Brattain, and William
Shockley. The transistor, which essentially functions as a solid-state electronic switch, replaced the much less suitable
vacuum tube. Because the transistor was so much smaller and consumed significantly less power, a computer system built with
transistors was much smaller, faster, and more efficient than a computer system built with vacuum tubes.
The conversion to transistors began the trend toward miniaturization. The normal laptop (or palmtop) PC systems, which
run on batteries, have more computing power than many earlier systems that filled rooms and consumed huge amounts of electrical
In 1959, engineers at Texas Instruments invented the integrated circuit (IC), a semiconductor circuit that contains
more than one transistor on the same base (or substrate material) and connects the transistors without wires. The first IC
contained only six transistors. By comparison, the Intel Pentium Pro microprocessor used in many high-end systems has more
than 5.5 million transistors, and the integral cache built into some of these chips contains as many as an additional 32 million
In 1969, Intel introduced a 1K-bit memory chip, which was much larger than anything else available at the time. (1K bits
equals 1,024 bits, and a byte equals 8 bits. This chip, therefore, stored only 128 bytes.) Because of Intel's success in chip
manufacturing and design, Busicomp, a Japanese calculator manufac-turing company, asked Intel to produce 12 different logic
chips for one of its calculator designs. Rather than produce 12 separate chips, Intel engineers included all the functions
of the chips in a single chip.
In addition to incorporating all the functions and capabilities of the 12-chip design into one multipurpose chip, the engineers
designed the chip to be controlled by a program that could alter the function of the chip. The chip then was generic in nature,
meaning that it could function in designs other than calculators. Previous designs were hard-wired for one purpose, with built-in
instructions; this chip would read from memory a variable set of instructions that would control the function of the chip.
The idea was to design almost an entire computing device on a single chip that could perform different functions, depending
on what instructions it was given.
The first microprocessor--the Intel 4004, a 4-bit processor--was introduced in 1971. The chip operated on 4 bits of data
at a time. The successor to the 4004 chip was the 8008 8-bit microprocessor, introduced in 1972.
In 1973, some of the first microcomputer kits based on the 8008 chip were developed. These kits were little more than demonstration
tools and did little except blink lights. In late 1973, Intel introduced the 8080 microprocessor, which was 10 times faster
than the earlier 8008 chip and addressed 64K of memory. This breakthrough was the one that the personal computer industry
had been waiting for.
MITS introduced the Altair kit in a cover story in the January 1975 issue of Popular Electronics magazine. The Altair
kit, considered to be the first personal computer, included an 8080 processor, a power supply, a front panel with a large
number of lights, and 256 bytes (not kilobytes) of memory. The kit sold for $395 and had to be assembled. The computer included
an open architecture bus (slots) that prompted various add-ons and peripherals from aftermarket companies. The new processor
inspired other companies to write programs, including the CP/M (Control Program for Microprocessors) operating system and
the first version of the Microsoft BASIC (Beginners All-purpose Symbolic Instruction Code) programming language.
IBM introduced what can be called its first personal computer in 1975. The Model 5100 had 16K of memory, a built-in
16-line-by-64-character display, a built-in BASIC language interpreter, and a built-in DC-300 cartridge tape drive for storage.
The system's $9,000 price placed it out of the mainstream personal computer marketplace, which was dominated by experimenters
(affectionately referred to as hackers) who built low-cost kits ($500 or so) as a hobby. The IBM system obviously was
not in competition for this low-cost market and did not sell well.
The Model 5100 was succeeded by the 5110 and 5120 before IBM introduced what we know as the IBM Personal Computer (Model
5150). Although the 5100 series preceded the IBM PC, the older systems and the 5150 IBM PC had nothing in common. The PC IBM
turned out was more closely related to the IBM System/23 DataMaster, an office computer system introduced in 1980. In fact,
many of the engineers who developed the PC at IBM had originally worked on the DataMaster.
In 1976, a new company called Apple Computer introduced the Apple I, which sold for $695. This system consisted of a main
circuit board screwed to a piece of plywood; a case and power supply were not included. Only a few of these computers were
made, and they reportedly have sold to collectors for more than $20,000. The Apple II, introduced in 1977, helped set the
standard for nearly all the important microcomputers to follow, including the IBM PC.
The microcomputer world was dominated in 1980 by two types of computer systems. One type, the Apple II, claimed a large
following of loyal users and a gigantic software base that was growing at a fantastic rate. The other type, CP/M systems,
consisted not of a single system but of all the many systems that evolved from the original MITS Altair. These systems were
compatible with one another and were distinguished by their use of the CP/M operating system and expansion slots, which followed
the S-100 (for slots with 100 pins) standard. All these systems were built by a variety of companies and sold under various
names. For the most part, however, these companies used the same software and plug-in hardware. It is interesting to note
that none of these systems were PC-compatible, or Mac-compatible, the two primary standards!
The IBM Personal Computer
At the end of 1980, IBM decided to truly compete in the rapidly growing low-cost personal computer market. The company
established what then was called the Entry Systems Division, located in Boca Raton, Florida, to develop the new system. This
small group consisted of 12 engineers and designers under the direction of Don Estridge; the team's chief designer was Lewis
Eggebrecht. The division developed IBM's first real PC. (IBM considered the 5100 system, developed in 1975, to be an intelligent
programmable terminal rather than a genuine computer, even though it truly was a computer.) Nearly all these engineers had
been moved to the new division from the System/23 DataMaster project, which in 1980 introduced a small office computer system
that was the closest predecessor to the IBM PC.
Much of the PC's design was influenced by the DataMaster's design. In the DataMaster's single-piece design, the display
and keyboard were integrated into the unit. Because these features were limiting, they became external units on the PC, although
the PC keyboard layout and electrical designs were copied from the DataMaster.
Several other parts of the IBM PC system also were copied from the DataMaster, including the expansion bus (or input/output
slots), which included not only the same physical 62-pin connector but also almost identical pin specifications. This copying
was possible because the PC used the same interrupt controller as the DataMaster and a similar direct memory access (DMA)
controller. Expansion cards already designed for the DataMaster could then be easily re-designed to function in the PC.
The DataMaster used an Intel 8085 CPU, which had a 64K address limit, as well as an 8-bit internal and external data bus.
This arrangement prompted the PC design team to use the Intel 8088 CPU, which offered a much larger (1M) memory address limit,
and an internal 16-bit data bus, but only an 8-bit external data bus. The 8-bit external data bus and similar instruction
set allowed the 8088 to be easily interfaced into the earlier DataMaster designs.
Estridge and the design team rapidly developed the design and specifications for the new system. In addition to borrowing
from the System/23 DataMaster, the team studied the marketplace, which also had enormous influence on the IBM PC's design.
The designers looked at the prevailing standards, learned from the success of those systems, and incorporated into the new
PC all the features of the popular systems--and more. With the parameters for design made obvious by the market, IBM produced
a system that filled its niche in the market perfectly.
IBM brought its system from idea to delivery in one year by using existing designs and purchasing as many components as
possible from outside vendors. The Entry Systems Division was granted autonomy from IBM's other divisions and could tap resources
outside the company, rather than go through the bureaucratic procedures that required exclusive use of IBM resources. IBM
contracted out the PC's languages and operating system to a small company named Microsoft. That decision would be the major
factor in establishing Microsoft as the dominant force in PC software.
NOTE: It is interesting to note that IBM had originally contacted Digital Research (the
company that created CP/M, then the most popular Personal Computer operating system) to have them develop an operating system
for the new IBM PC, but they were leery of working with IBM, and especially balked at the non-disclosure agreement IBM wanted
them to sign. Microsoft jumped on the opportunity left open by Digital Research, and as a result has become one of the largest
software companies in the world. IBM's use of outside vendors in developing the PC was an open invitation for the aftermarket
to jump in and support the system--and it did.
On Wednesday, August 12, 1981, a new standard was established in the micro- computer industry with the debut of the IBM
PC. Since then, hundreds of millions of PC-compatible systems have been sold as the original PC has grown into an enormous
family of computers and peripherals. More software has been written for this computer family than for any other system on
The Growing IBM-Compatible Marketplace
For example, 15 years since the original IBM PC was introduced, many changes were made in the IBM-compatible PC. It advanced
from a 4.77MHz 8088-based system to a 300MHz Pentium II-based system--nearly 2,000 times faster than the original IBM
PC (in actual processing speed, not just clock speed). The original PC had only one or two single-sided floppy drives that
stored 160K each using DOS 1.0, whereas systems 16 years later easily could have 10G (10 billion bytes) or more of hard disk
In addition to performance and storage capacity, another major change since the original IBM PC was introduced is that
IBM is not the only manufacturer of "PC-compatible" systems. IBM originated the PC-compatible standard, of course, and it
continues to set standards that compatible systems follow, but the company does not dominate the PC market as it did originally.
More often than not, new standards in the PC industry were developed by companies and organizations other than IBM. Later
it became Intel and Microsoft who were primarily responsible for developing and extending the PC hardware and software standards,
Even so, there are literally hundreds of system manufacturers producing computers that are fully PC compatible, not to
mention the thousands of peripheral manufacturers whose components expand and enhance PC-compatible systems.
PC-compatible systems have thrived, not only because compatible hardware can be assembled easily, but also because the
primary operating system was available not from IBM but from a third party (Microsoft). The core of the system software is
the BIOS (Basic Input Output System), and this was also available from third-party companies like AMI, Award, Phoenix, and
others. This situation allowed other manufacturers to license the operating system and BIOS software and to sell their own
compatible systems. The fact that DOS borrowed the functionality and user interface from both CP/M and UNIX probably had a
lot to do with the amount of software that became available. Later, with the success of Windows, there would be even more
reasons for software developers to write programs for PC-compatible systems.
One of the reasons why Apple Macintosh systems did never enjoy the success of PC-compatibles is that Apple controlled all
the software (BIOS and OS), and did not license any of it to other companies for use in compatible systems. It is fortunate
for the computing public as a whole that IBM created a more open and extendible standard. The competition among manufacturers
and vendors of PC-compatible systems is the reason why such systems offer so much performance and so many capabilities for
The IBM-compatible market continues to thrive and prosper. New technology continues to be integrated into these systems,
enabling them to grow with the times. Because of the high value that these types of systems can offer for the money and the
large amount of software that is available to run on them, PC-compatible systems likely will continue dominating the personal