Sometimes referred to as Big Iron, mainframe computers are particularly large computers with considerably more processing power than most other classes of computers.

Early computers were very large and heavy. The cabinets that housed the central processing unit and main memory of these computers were known as main frames. Because these were the parts of the computer that people saw, the entire units eventually became known as mainframes.

Each of these early mainframes were one of a kind, and a dedicated crew of programmers and system engineers were required in order to keep them running. They were housed in specially air-conditioned rooms with raised floors and access control.

They ran one job at a time, using punch cards as input, and output was printed onto reams of wide, green-striped paper made especially for that purpose. Data was collected on reels of magnetic tape or in trays of punch cards.

At that time, computers were used primarily for business accounting and scientific calculations, so these computers were owned either by large corporations or university systems.

Most of the time, these hugely expensive mainframe computers were sitting idle. Eventually, this led to the concept of timesharing, as a way to increase the efficiency of the mainframe. The idea was to connect remote terminals to the mainframe, allowing access to the computer from multiple locations. In this way, there would always be a useful program running.

This idea evolved into the client-server architecture that is so common today, where the remote clients had some computing and storage capabilities of their own, while still relying on the computing power of the mainframe as the server.

As computer technology advanced, the amount of computing power went up while the size went down. While a mainframe was originally a reference to computer systems that filled large rooms, the term was later used to distinguish high-end commercial machines from less powerful units. While they are still larger than the home computers that most of us are familiar with, they don't necessarily fill large rooms today, although some of them do.

Only a few years ago, IBM's server business was made up of computers that were built on the x86 architecture. You may remember your first 286 or 386DX computer. That's what the x86 stands for. It refers to the type of chip architecture used. Mainframes today use a new type of architecture known as z/Architecture. The main advantage of the newer architecture is that the newer mainframes can encrypt data eighteen times faster than the x86 platforms at five percent of the cost.

These mainframes are highly stable and reliable. They can run uninterrupted for very long periods of time, even decades between failures. As they are used in situations where downtime would be costly, they are known for their reliability, availability, and serviceability.

Although there are more mainframes in use today than ever, they are smaller. Because they are less costly, they are not financially restricted to only the larger corporations and universities.

It is easy to confuse supercomputers and mainframes, given that they both tend to be large, expensive, and powerful. They can be distinguished by the tasks they perform. While a supercomputer focus on fast computation of complex mathematical operations, a mainframe acts as a server and supports a large database, vast input-output devices, and multiprogramming. A supercomputer is used to run one program very fast, while a mainframe might run millions of programs at the same time. Mainframe computers are large, fast, and expensive computes, but they are smaller, slower, and less expensive than supercomputers.

From the late 1950s through the 1990s, several manufacturers produced mainframe computers. In the United States, IBM was dominant. Other significant manufacturers included Burroughs, UNIVAC, NCR, Control Data, Honeywell, General Electric, and RCA. Notable manufacturers outside the United States were Fujitsu, Hitachi, NEC, Oki, Olivetti, Siemens, and Telefunken.

The focus of this category is on mainframe computers, historical or contemporary.

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