The fourth generation of computers began around 1975 and lasted until around 1985. It recognizes that period in computer history when the integrated circuit chip became the microprocessor, a “computer on a chip.” As a result, the first functional desktop computers emerged, beginning with experimental hobbyist DIY models such as the Altair 8800 mail-order kit, and progressing to early commercial models such as the Commodore and Tandy TRS-80. The period marks the successful introduction and mass production of the first desktop models of the IBM PC, its various clones, and the Apple Macintosh.
A star of the previous generation of computers had been the Control Data CD 1604 computer of the 1960s. To process data it had some 25,000 transistors and 100,000 diodes among thousands of resistors and capacitors, all individually connected to each other.
The microprocessor was well on its way to doing everything the CD 1604 did on a single chip. It was born when Intel researchers integrated all arithmetic, logic, and control processing functions onto a single chip through a photolithography process.
The CPU read incoming data and instructions as bytes of 8-bit code. Reading involved performing arithmetic and logical calculations on the code. The resulting data and instructions further enabled control functions to order the code into multiple data streams that were written or received as graphics output on a monitor.
The embedded microprocessor chip became known as the central processing unit, the CPU, or the “brain” of the model computer. His input enhanced the earlier 1958-1959 inventions of the integrated circuit chip by Jack Kilby, at Texas Instruments, and Robert Noyce, then at Fairchild Semiconductor. These two engineers independently miniaturized the transistor and created the IC chip as a solid-state piece of silicon (or germanium). His discoveries had essentially ushered in the new age of solid-state electronics.
Kilby received the Nobel Prize for the IC chip, while Noyce continued its development as founder of the Intel Corporation. Meanwhile, solid-state miniaturization of electronic components immediately pushed the technology to new limits of advancement in space, defense, and consumer projects. By the 1970s, large scale integration (LSI) of tens of thousands of transistors on a chip would eventually lead to very large scale integration (VLSI) with millions and then billions of transistors per chip after the turn of the century .
Under Noyce, Intel released the first CPU state microprocessor, the 4004, on November 15, 1971. The company also developed the first random access memory chip, the RAM chip, to provide temporary storage for the CPU. The 4004 could process 60,000 (60K) instructions per second. It wasn’t until Intel produced the 8-bit 8080 microprocessor in April 1974 that the desktop revolution really began to flourish.
The 8080 had about 6,000 transistors miniaturized by photolithography on a microprocessor chip. It had a clock speed of 2 MHz and could process several hundred thousand instructions per second.
Hobbyists soon ordered the MITS Altair 8800, an entry-level computer using the 8080 microprocessor, after it was advertised on the 1975 cover of Popular Electronics. Bill Gates and Paul Allen had designed an interpreter unit for the BASIC programming language to boot up and instruct the computer.
In 1976, Steve Wozniak and Steve Jobs founded Apple Computer, Inc to begin experimenting with their first computer models. They used the Z80 microprocessor as the CPU. The two founders began mass-producing their Apple II microcomputer in 1977.
Xerox, Inc. was a major experimenter in early desktop technologies. In the mid-1970s, Xerox had created a desktop version of a minicomputer system called the Alto, at its Palo Alto Research Center. Xerox had done a lot of research on the use of graphics. All early desktop models used command line controls where the user typed a line of command at the command prompt. Early desktop manufacturers like Steve Jobs visited Xerox PARC and got ideas about graphical user interfaces and the mouse.
Other third-generation computing milestones include the arrival of the IBM PC, with an operating system from Microsoft, and the 1984 introduction of the Apple Macintosh. IBM released the first version of its IBM PC in August 1981. By 1982, it shipped with MS-DOS as the operating system. The next advanced model was the IBM PC/AT released in August 1984, based on the 16-bit Intel 80286 CPU with 134,000 transistors. This CPU could reach a speed of 8Mhz. Many clones based on the IBM-PC models were produced, notably from Compac.
In distinctive style, during a Super Bowl XVIII commercial on January 22, 1984, Apple released the Macintosh desktop computer. Establishing Apple’s trademark, the Macintosh became known for its compelling graphics capabilities. The system, with a 16-bit 68k Motorola CPU, was proprietary and could not be cloned.