The earliest computers, which came into widespread use in the 1960s, were known as mainframes. The photo shows an IBM 704 mainframe in 1964. According to Whatis.com:
“A mainframe (also known as “big iron”) is a high-performance computer used for large-scale computing purposes that require greater availability and security than a smaller-scale machine can offer.
Historically, mainframes have been associated with centralized rather than distributed computing, although that distinction is blurring as smaller computers become more powerful and mainframes become more multi-purpose. Today, IBM emphasizes that their mainframes can be used to serve distributed users and smaller servers in a computing network.”
“The original mainframes were housed in room-sized metal frames, which is probably where the name derives from. In the past, a typical mainframe might have occupied 2,000 – 10,000 square feet. Newer mainframes are about the same size as a large refrigerator.”
Mainframes later faced competition from minicomputers. The picture shows a PDP 11/40, made by Digital Computers, now on display in Vienna Technical Museum. According to Wikipedia:
“Minicomputer (colloquially, mini) is a term for class of smaller computers that evolved in the mid 1960s and sold for much less than mainframe and mid-size computers from IBM and its direct competitors. In a 1970 survey, the New York Times suggested a consensus definition of a minicomputer as a machine costing less than $25,000, with an input-output device such as a teleprinter and at least 4K words of memory, that is capable of running programs in a higher level language such as Fortran or Basic.
When single chip CPUs appeared, beginning with the Intel 4004 in 1971, the term minicomputer came to mean a machine that lies in the middle range of the computing spectrum, in between the smallest mainframe computers and the microcomputers. The term minicomputer is little used today; the contemporary term for this class of system is midrange computer.”
Microcomputers were initially introduced in the early 1970s. Some of the earliest models were sold as kits assembly by users, but these were soon replaced by ready-built models, such as the Commodore 64, The Tandy TRS-80 and the BBC Micro. These were initially seen as hobbyist machines, but with the introduction of business-oriented software, such as word-processors and spreadsheets, they became increasingly useful as business machines. Microcomputers could fit under a desk, putting them within easy reach of users, unlike minicomputers or mainframes which took up large cabinets or even dedicated rooms.
In the early 1980s IBM introduced the IBM PC, which was soon cloned by other manufacturers. The term “personal computer”, or simply PC, took over from “microcomputer”. personal computers standardised around IBM PC compatibles running DOS, and later Windows. Modern desktop computers, video game consoles, laptops, tablet PCs, and many types of handheld devices can be considered as microcomputers.
Modern microcomputers come in a variety of formats. Monitors, keyboards and other I/O devices can be integrated or separate. A microcomputer has at least one type of data storage, usually Random Access Memory (RAM), along with some kind of backing storage, such as hard disks or memory cards.
The remainder of this course will focus on microcomputers in their various forms.