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The fourth generation of the modern computer includes those that incorporate microprocessors in their designs.Of course, part of this fourth generation of computers is the personal computer, which itself was made possible by the advent of low-cost microprocessors and memory.
In 1973, some of the first microcomputer kits based on the 8008 chip were developed. These kits were little more than demonstration tools and didn’t do much except blink lights. In April 1974, Intel introduced the 8080 microprocessor, which was 10 times faster than the earlier 8008 chip and addressed 64 KB of memory. This was the breakthrough that the personal computer industry had been waiting for.
A company called MITS introduced the Altair 8800 kit in a cover story in the January 1975 issue of Popular Electronics. The Altair kit, considered by many 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. Assembly back then meant you got out your soldering iron to actually finish the circuit boards—not like today, where you can assemble a system of premade components with nothing more than a screwdriver.
Micro Instrumentation and Telemetry Systems was the original name of the company founded in 1969 by Ed Roberts and several associates to manufacture and sell instruments and transmitters for model rockets. Ed Roberts became the sole owner in the early 1970s, after which he designed the Altair. By January 1975, when the Altair was introduced, the company was called MITS, Inc., which then stood for nothing more than the name of the company. In 1977, Roberts sold MITS to Pertec, moved to Georgia, went to medical school, and became a practicing physician. Considered by many to be the “father of the personal computer,” Roberts passed away in 2010 after a long bout with pneumonia.
The Altair included an open architecture system bus later called the S-100 bus, so named because it became an industry standard and had 100 pins per slot. The S-100 bus was widely adopted by other computers that were similar to the Altair, such as the IMSAI 8080, which was featured in the movie WarGames. The S-100 bus open architecture meant that anybody could develop boards to fit in these slots and interface to the system, and it ensured a high level of cross-compatibility between different boards and systems.The popularity of 8080 processor–based systems inspired software companies to write programs, including the CP/M (control program for microprocessors) OS 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 16 KB 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 $8975 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. Obviously, the IBM system was not in competition for this low-cost market and did not sell as well by comparison.
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 that 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 IBM PC had originally worked on the DataMaster.
In 1976, a new company called Apple Computer introduced the Apple I, which originally sold for $666.66. The selling price was an arbitrary number selected by one of Apple’s cofounders, Steve Jobs. 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 OS and expansion slots, which followed the S-100 standard. All these systems were built by a variety of companies and sold under various names. For the most part, however, these systems used the same software and plug-in hardware.It is interesting to note that none of these systems was PC compatible or Macintosh compatible, the two primary standards in place today.
A new competitor looming on the horizon was able to see that to be successful, a personal computer needed to have an open architecture, slots for expansion, a modular design, and healthy support from both hardware and software companies other than the original manufacturer of the system. This competitor turned out to be IBM, which was quite surprising at the time because IBM was not known for systems with these open-architecture attributes. IBM, in essence, became more like the early Apple, whereas Apple became like everybody expected IBM to be. The open architecture of the forthcoming IBM PC and the closed architecture of the forthcoming Macintosh caused a complete turnaround in the industry.