The fourth generation of computers began around 1975 and lasted until around 1985. Recognize that period in computer history when the integrated circuit chip evolved into the microprocessor, a “computer on a chip.” As a result, the first functional desktops appeared, starting with experimental hobbyist DIY models like the Altair 8800 mail order kit and progressing to early commercial models like 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 the data, it had about 25,000 transistors and 100,000 diodes among thousands of resistors and capacitors, all connected individually.

The microprocessor was on its way to doing all the things the CD 1604 did on a chip. It had its birth when Intel researchers integrated all arithmetic, logic, and control processing functions together on one chip through a photolithography process.

The CPU reads data and instructions that come as bytes of 8-bit code. Reading involved performing arithmetic and logic calculations on the code. The resulting data and instructions further enabled control functions to sort code into various 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 computer model. His entry emphasized 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 had independently miniaturized the transistor and created the IC chip as a piece of solid-state silicon (or germanium). His discoveries had essentially ushered in the new era of solid state electronics.

Kilby received the Nobel Prize for the IC chip, while Noyce continued his development as the founder of Intel Corporation. Meanwhile, the solid-state miniaturization of electronic components immediately pushed the technology to new limits of advancement in space, defense, and consumer projects. In 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 state-of-the-art CPU 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 8080 8-bit microprocessor, in April 1974, that the desktop computer revolution really began to flourish.

The 8080 had about 6,000 photolithography miniaturized transistors on a microprocessor chip. It had a 2 MHz clock speed and could process several hundred thousand instructions per second.

Soon, fans were buying the MITS Altair 8800, a bare-knuckle computer using the 8080 microprocessor, after it was advertised on the 1975 cover of Popular Electronics. Bill Gates and Paul Allen had designed an interpretation unit for the BASIC programming language to start and instruct the computer.

In 1976, Steve Wozniak and Steve Jobs founded Apple Computer, Inc to begin experiments 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 built a desktop version of a minicomputer system called 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 in which the user entered a line of instructions at the command prompt. Early desktop manufacturers such as Steve Jobs visited Xerox PARC and received ideas about graphical user interfaces and the mouse.

Other third-generation computing milestones include the advent of the IBM PC, with a Microsoft operating system, and the introduction in 1984 of the Apple Macintosh. IBM released the first version of its IBM PC in August 1981. In 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 were produced based on the IBM-PC models, particularly 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 attractive graphics capabilities. The system, with a 16-bit 68k Motorola CPU, was proprietary and could not be cloned.