Mainframe computer provide enormous processing power to large companies.
Technology advances since the introduction of the mainframe computer in the mid-20th century have blurred the distinctions between mainframes and large servers, but there are still distinctions that classify some computing machines as mainframe computers -- including speed, total throughput, environmental considerations and operating systems. Mainframe computers are alive and well, evidenced by the fact that IBM announced the release the zEnterprise mainframe in July of 2010.
Mainframe Computer Definition
The classic definition of a mainframe computer is a machine that produces high computing performance that is used by large companies which have matching large-scale computing requirements. A mainframe provides greater reliability, availability and security than their smaller counterparts. Mainframes are typically used in centralized computing environments as opposed to distributed environments, and are generally considered to be much more adept at multi-purpose computing than smaller servers.
Size - Then and Now
In the early years, mainframe computers took up huge rooms of "frames" of vacuum tubes and wires, all tied to a central "main frame," hence the term "mainframe." The ENIAC computer consumed 680 square feet of floor space and contained more than 17,000 vacuum tubes. The UNIVAC computer held 5,000 vacuum tubes and introduced the ability to store data on magnetic tape rather than punched cards. The modern IBM S/390 mainframe stands in stark contrast, taking up a footprint of about eleven square feet and processing billions of instructions per second.
Processor Speed and Throughput
Processing speed requirements prompt companies to buy mainframes. Large banks and other financial institutions, conglomerate enterprises with multiple operating units and other large businesses require raw speed and transaction throughput to be able to process a day's business in less than 24 hours. While some larger servers deliver solid processor speed, it is the combination of processing capability, including the rapid turnaround of data, that makes the mainframe computer superior.
Dueling Operating Systems
One of the biggest differences in servers and mainframes concerns the operating systems that actually run the machines. Departmental servers are known for running operating systems such as Unix, Linux and Microsoft Windows Server. While these OSs have their rightful places, they do not compare to the capabilities of mainframe operating systems such as OS/390, VM/ESA, MVS, VSE/ESA, S/390 and z/OS. Modern mainframes are capable of running several of these operating systems concurrently. It is also important to remember that mainframe computer operating system writers pioneered the idea of "virtual machines."
Costs
Mainframe computers are very powerful machines that manage a vast array of resources such as multiple processors, large amounts of main memory and external storage devices, and process information at tremendous speed. Accordingly, mainframes are very expensive, costing millions of dollars, making them a major capital investment for governments, large companies and universities.
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