"Microcomputer" is an antiquated term that refers to a computer that uses a microprocessor (integrated circuit) for its central processing unit (CPU). In addition, this type of computer should be small enough to fit on a desk, as microprocessor-based computers larger than that are generally called "minicomputers" instead. Microprocessor-based computers are the backbone of the modern computer era, often considered "third generation" computers, in contrast to the first and second generation of vacuum tubes and bipolar junction transistors, which were common before the microprocessor was developed. Today, almost all computers are microcomputers.
Computers were relatively slow and expensive throughout the 1940s, 1950s, and 1960s, often requiring large amounts of power and room-sized mainframes. Even a computer the size of a refrigerator could be called a "minicomputer," due to its comparatively small size. At this point, computers were only available to the government, universities, and large companies, and had to be used on timeshare. In 1958, however, Jack Kilby invented the integrated circuit, which opened up the possibility of much smaller computers.
In the late 1960s and early 1970s, minicomputers carried the day, being based on integrated circuits but too large to be called microcomputers. As early as 1956, Isaac Asimov wrote about the possibility of small personal computers, and by the mid-1970s, they had become technologically possible. In 1974, Intel released the Intel 8080, what has been called the first truly usable microprocessor. This circuit was then installed in many computers, such as the Altair 8800, which were the first true microcomputers. Among the early users were Bill Gates and Steve Ballmer, roommates at Harvard who would go on to found the software behemoth Microsoft.
In the early and mid-1980s, microcomputers began to slowly edge out of the realm of the nerd and into the mainstream. The Apple II, which launched Apple Computer to fame, had been released in 1977, and more and more people began to realize its utility for business and in education. Throughout the 1980s, Apple released more machines that were progressively smaller and more powerful, increasing the appeal of personal computers. Many competitors emerged, running operating systems like DOS and Windows®. Today, there are over a billion computers in use worldwide.