Computer History

The history of personal computer as mass-market consumer electronic devices effectively began in 1977 with the introduction of microcomputers, although some mainframe and main computers had been applied as single-user systems much earlier. A personal computer is one intended for interactive individual use, as opposed to amainframe computer where the end user's requests are filtered through operating staff, or a time sharing system in which one large processor is shared by many individuals. After the development of the microprocessor, individual personal computers were low enough in cost that they eventually became affordable consumer goods. Early personal computers – generally called microcomputers– were sold often in electronic kit form and in limited numbers, and were of interest mostly to hobbyists and technicians.

Six years later a manufacturer took the risk of referring to their product this way, when Hewlett-Packard advertised their "Powerful Computing Genie" as "The New Hewlett-Packard 9100A personal computer". This advertisement was deemed too extreme for the target audience and replaced with a much drier ad for the HP 9100 A programmable calculator.

Over the next seven years the phrase had gained enough recognition that when Byte magazine published its first edition, it referred to its readers as "[in] the personal computing field", and Creative Computing defined the personal computer as a "non-(time)shared system containing sufficient processing power and storage capabilities to satisfy the needs of an individual user." Two years later, when what Byte was to call the "1977 Trinity" of pre-assembled small computers hit the markets, the Apple II and the PET 2001 were advertised as personal computers, while the TRS-80 was a described as a microcomputer used for household tasks including "personal financial management". By 1979 over half a million microcomputers were sold and the youth of the day had a new concept of the personal computer.

Mainframes, minicomputers, and microcomputers
Microprocessor and cost reduction
Home brew Computer Club

Computer terminals were used for time sharing access to central computers. Before the introduction of the microprocessor in the early 1970s, computers were generally large, costly systems owned by large corporations, universities, government agencies, and similar-sized institutions. End users generally did not directly interact with the machine, but instead would prepare tasks for the computer on off-line equipment, such as card punches. A number of assignments for the computer would be gathered up and processed in batch mode. After the job had completed, users could collect the results. In some cases it could take hours or days between submitting a job to the computing center and receiving the output.

A more interactive form of computer use developed commercially by the middle 1960s. In a time-sharing system, multiple computer terminals let many people share the use of one mainframe computer processor. This was common in business applications and in science and engineering.

A different model of computer use was foreshadowed by the way in which early, pre-commercial, experimental computers were used, where one user had exclusive use of a processor.In places such as MIT, students with access to some of the first computers experimented with applications that would today be typical of a personal computer; for example, computer aided drafting was foreshadowed by T-square, a program written in 1961, and an ancestor of today's computer games was found in Space war! in 1962. Some of the first computers that might be called "personal" were early minicomputers such as the LINC and PDP-8, and later on VAX and larger minicomputers from Digital Equipment Corporation (DEC), Data General, Prime Computer, and others. By today's standards they were very large (about the size of a refrigerator) and cost prohibitive (typically tens of thousands of US dollars). However, they were much smaller, less expensive, and generally simpler to operate than many of the mainframe computers of the time. Therefore, they were accessible for individual laboratories and research projects. Minicomputers largely freed these organizations from the batch processing and bureaucracy of a commercial or university computing center.

In addition, minicomputers were relatively interactive and soon had their own operating systems. The minicomputer Xerox Alto (1973) was a landmark step in the development of personal computers, because of its graphical user interface, bit-mapped high resolution screen, large internal and external memory storage, mouse, and special software.

As early as 1945, Vannevar Bush, in an essay called As We May Think, outlined a possible solution to the growing problem of information storage and retrieval. In what was later to be called The Mother of All Demos, SRI researcher Douglas Engelbart in 1968 gave a preview of what would become the staples of daily working life in the 21st century – e-mail, hypertext, word processing, video conferencing, and the mouse. The demo was the culmination of research in Engelbart's Augmentation Research Center laboratory, which concentrated on applying computer technology to facilitate creative human thought.

The minicomputer ancestors of the modern personal computer used early integrated circuit (microchip) technology, which reduced size and cost, but they contained no microprocessor. This meant that they were still large and difficult to manufacture just like their mainframe predecessors. After the "computer-on-a-chip" was commercialized, the cost to manufacture a computer system dropped dramatically. The arithmetic, logic, and control functions that previously occupied several costly circuit boards were now available in one integrated circuit, making it possible to produce them in high volume. Concurrently, advances in the development of solid state memory eliminated the bulky, costly, and power-hungry magnetic core memory used in prior generations of computers.

A few researchers at places such as SRI and Xerox PARC were working on computers that a single person could use and that could be connected by fast, versatile networks: not home computers, but personal ones.

After the 1972 introduction of the Intel 4004, microprocessor costs declined rapidly. In 1974 the American electronics magazine Radio-Electronics described the Mark-8 computer kit, based on the Intel 8008 processor. In January of the following year, Popular Electronics magazine published an article describing a kit based on the Intel 8080, a somewhat more powerful and easier to use processor. The Altair 8800 sold remarkably well even though initial memory size was limited to a few hundred bytes and there was no software available. However, the Altair kit was much less costly than an Intel development system of the time and so was purchased by companies interested in developing microprocessor control for their own products. Expansion memory boards and peripherals were soon listed by the original manufacturer, and later by plug compatible manufacturers. The very first Microsoft product was a 4 kilobyte paper tape BASIC interpreter, which allowed users to develop programs in a higher-level language. The alternative was to hand-assemble machine code that could be directly loaded into the microcomputer's memory using a front panel of toggle switches, push buttons and LED displays. While the hardware front panel emulated those used by early mainframe and minicomputers, after a very short time I/O through a terminal was the preferred human/machine interface, and front panels became extinct.

Although the Altair spawned an entire business, another side effect it had was to demonstrate that the microprocessor had so reduced the cost and complexity of building a microcomputer that anyone with an interest could build their own. Many such hobbyists met and traded notes at the meetings of the Homebrew Computer Club (HCC) in Silicon Valley. Although the HCC was relatively short-lived, its influence on the development of the modern PC was enormous.

Members of the group complained that microcomputers would never become commonplace if they still had to be built up, from parts like the original Altair, or even in terms of assembling the various add-ons that turned the machine into a useful system. What they felt was needed was an all-in-one system. Out of this desire came the Sol-20 computer, which placed an entire S-100 system – QWERTY keyboard, CPU, display card, memory and ports – into an attractive single box. The systems were packaged with a cassette tape interface for storage and a 12" monochrome monitor. Complete with a copy of BASIC, the system sold for US$2,100. About 10,000 Sol-20 systems were sold.

Although the Sol-20 was the first all-in-one system that we would recognize today, the basic concept was already rippling through other members of the group, and interested external companies.