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A mainframe computer, informally called a mainframe or big iron, is a
computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known as Computer program, programs. These programs enable compu ...

computer
used primarily by large organizations for critical applications like bulk
data processing Data processing is, generally, "the collection Collection or Collections may refer to: * Cash collection, the function of an accounts receivable department * Collection agency, agency to collect cash * Collections management (museum) ** Collec ...

data processing
for tasks such as
censuses A census is the procedure of systematically enumerating, and acquiring and recording information about the members of a given Statistical population, population. This term is used mostly in connection with Population and housing censuses by country ...

censuses
, industry and consumer
statistics Statistics is the discipline that concerns the collection, organization, analysis, interpretation, and presentation of data. In applying statistics to a scientific, industrial, or social problem, it is conventional to begin with a statistical ...

statistics
,
enterprise resource planning Enterprise resource planning (ERP) is the integrated management of main business processes, often in real time and mediated by software and technology. ERP is usually referred to as a category of business management software—typically a sui ...
, and large-scale
transaction processing Transaction processing is information processing in computer science that is divided into individual, indivisible operations called ''transactions''. Each transaction must succeed or failure, fail as a complete unit; it can never be only partiall ...
. A mainframe computer is large but not as large as a
supercomputer File:Supercomputer-power-flops.svg, upright=1.5, Computing power of the top 1 supercomputer each year, measured in FLOPS A supercomputer is a computer with a high level of performance as compared to a general-purpose computer. The performance ...

supercomputer
and has more processing power than some other classes of computers, such as
minicomputer A minicomputer, or colloquially mini, is a class of smaller general purpose computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform gen ...
s, servers,
workstation A workstation is a special computer designed for technical or computational science, scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating ...

workstation
s, and
personal computer A personal computer (PC) is a multi-purpose computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern computers can perform generic sets of operations known a ...
s. Most large-scale computer-system architectures were established in the 1960s, but they continue to evolve. Mainframe computers are often used as servers. The term ''mainframe'' was derived from the large cabinet, called a ''main frame'', that housed the
central processing unit A central processing unit (CPU), also called a central processor, main processor or just processor, is the electronic circuit 200px, A circuit built on a printed circuit board (PCB). An electronic circuit is composed of individual electroni ...

central processing unit
and main
memory Memory is the faculty of the by which or is , stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If s could not be remembered, it would be impossible for language, r ...
of early computers. Later, the term ''mainframe'' was used to distinguish high-end commercial computers from less powerful machines.


Design

Modern mainframe design is characterized less by raw computational speed and more by: * Redundant internal engineering resulting in high reliability and security * Extensive input-output ("I/O") facilities with the ability to offload to separate engines * Strict
backward compatibility Backward compatibility (sometimes known as backwards compatibility) is a property of a system, product, or technology that allows for interoperability Interoperability is a characteristic of a product or system, whose interfaces are completely ...
with older software * High hardware and computational utilization rates through virtualization to support massive
throughput In general terms, throughput is the rate of production or the rate at which something is processed. When used in the context of communication networks, such as Ethernet Ethernet () is a family of wired ing technologies commonly used in s ...
. * Hot-swapping of hardware, such as processors and memory. Their high stability and reliability enable these machines to run uninterrupted for very long periods of time, with
mean time between failures Mean time between failures (MTBF) is the predicted elapsed time between inherent failures of a mechanical or electronic system, during normal system operation. MTBF can be calculated as the arithmetic mean (average) time between failures of a syste ...
(MTBF) measured in decades. Mainframes have
high availability High availability (HA) is a characteristic of a system which aims to ensure an agreed level of operational performance, usually uptime, for a higher than normal period. Modernization has resulted in an increased reliance on these systems. For e ...
, one of the primary reasons for their longevity, since they are typically used in applications where downtime would be costly or catastrophic. The term
reliability, availability and serviceabilityReliability, availability and serviceability (RAS), also known as reliability, availability, and maintainability (RAM), is a computer hardware Computer hardware includes the physical parts of a computer A computer is a machine that can be p ...
(RAS) is a defining characteristic of mainframe computers. Proper planning and implementation are required to realize these features. In addition, mainframes are more secure than other computer types: the
NIST The National Institute of Standards and Technology (NIST) is a physical sciences Physical science is a branch of natural science that studies abiotic component, non-living systems, in contrast to life science. It in turn has many branches, e ...
vulnerabilities database,
US-CERT The United States Computer Emergency Readiness Team (US-CERT) is an organization within the Department of Homeland Security’s (DHS) Cybersecurity and Infrastructure Security Agency (CISA). Specifically, US-CERT is a branch of the Office of C ...
, rates traditional mainframes such as IBM Z (previously called z Systems, System z and zSeries), Unisys Dorado and Unisys Libra as among the most secure with vulnerabilities in the low single digits as compared with thousands for
Windows Microsoft Windows, commonly referred to as Windows, is a group of several proprietary {{Short pages monitor