Mainframe computers are computers used primarily by corporate and governmental organizations
for critical applications, bulk data processing such as census, industry and consumer statistics,
enterprise resource planning and transaction processing.
The term originally referred to the large cabinets called "main frames" that housed
the central processing unit and main memory of early computers. Later, the term was used
to distinguish high-end commercial machines from less powerful units. Most large-scale
computer system architectures were established in the 1960s, but continue to evolve.
Description Modern mainframe design is generally less
defined by single-task computational speed, and more by:
Redundant internal engineering resulting in high reliability and security
Extensive input-output facilities with the ability to offload to separate engines
Strict backward compatibility with older software High hardware and computational utilization
rates through virtualization to support massive throughput
Their high stability and reliability enables these machines to run uninterrupted for decades.
Software upgrades usually require setting up the operating system or portions thereof,
and are non-disruptive only when using virtualizing facilities such as IBM′s z/OS and Parallel
Sysplex, or Unisys′ XPCL, which support workload sharing so that one system can take
over another's application while it is being refreshed. Mainframes are defined by high
availability, one of the main reasons for their longevity, since they are typically
used in applications where downtime would be costly or catastrophic. The term reliability,
availability and serviceability is a defining characteristic of mainframe computers. Proper
planning and implementation is required to exploit these features, and if improperly
implemented, may serve to inhibit the benefits provided. In addition, mainframes are more
secure than other computer types: the NIST vulnerabilities database, US-CERT, rates traditional
mainframes such as IBM zSeries, Unisys Dorado and Unisys Libra as among the most secure
with vulnerabilities in the low single digits as compared with thousands for Windows, Unix,
and Linux. In the late 1950s, most mainframes had no
explicitly interactive interface. They accepted sets of punched cards, paper tape, or magnetic
tape to transfer data and programs. They operated in batch mode to support back office functions,
such as customer billing, and supported interactive terminals almost exclusively for applications
rather than program development. Typewriter and Teletype devices were also common control
consoles for system operators through the 1970s, although ultimately supplanted by keyboard/display
devices. By the early 1970s, many mainframes acquired interactive user interfaces and operated
as timesharing computers, supporting hundreds of users simultaneously along with batch processing.
Users gained access through specialized terminals or, later, from personal computers equipped
with terminal emulation software. By the 1980s, many mainframes supported graphical terminals,
and terminal emulation, but not graphical user interfaces. This format of end-user computing
reached mainstream obsolescence in the 1990s due to the advent of personal computers provided
with GUIs. After 2000, most modern mainframes have partially or entirely phased out classic
"green screen" terminal access for end-users in favour of Web-style user interfaces.
The infrastructure requirements were drastically reduced during the mid-1990s when CMOS mainframe
designs replaced the older bipolar technology. IBM claimed that its newer mainframes could
reduce data center energy costs for power and cooling, and that they could reduce physical
space requirements compared to server farms. Characteristics
Modern mainframes can run multiple different instances of operating systems at the same
time. This technique of virtual machines allows applications to run as if they were on physically
distinct computers. In this role, a single mainframe can replace higher-functioning hardware
services available to conventional servers. While mainframes pioneered this capability,
virtualization is now available on most families of computer systems, though not always to
the same degree or level of sophistication. Mainframes can add or hot swap system capacity
without disrupting system function, with specificity and granularity to a level of sophistication
not usually available with most server solutions. Modern mainframes, notably the IBM zSeries,
System z9 and System z10 servers, offer two levels of virtualization: logical partitions
and virtual machines. Many mainframe customers run two machines: one in their primary data
center, and one in their backup data center—fully active, partially active, or on standby—in
case there is a catastrophe affecting the first building. Test, development, training,
and production workload for applications and databases can run on a single machine, except
for extremely large demands where the capacity of one machine might be limiting. Such a two-mainframe
installation can support continuous business service, avoiding both planned and unplanned
outages. In practice many customers use multiple mainframes linked either by Parallel Sysplex
and shared DASD, or with shared, geographically dispersed storage provided by EMC or Hitachi.
Mainframes are designed to handle very high volume input and output and emphasize throughput
computing. Since the late-1950s, mainframe designs have included subsidiary hardware
which manage the I/O devices, leaving the CPU free to deal only with high-speed memory.
It is common in mainframe shops to deal with massive databases and files. Gigabyte to terabyte-size
record files are not unusual. Compared to a typical PC, mainframes commonly have hundreds
to thousands of times as much data storage online, and can access it much faster. Other
server families also offload I/O processing and emphasize throughput computing.
Mainframe return on investment, like any other computing platform, is dependent on its ability
to scale, support mixed workloads, reduce labor costs, deliver uninterrupted service
for critical business applications, and several other risk-adjusted cost factors.
Mainframes also have execution integrity characteristics for fault tolerant computing. For example,
z900, z990, System z9, and System z10 servers effectively execute result-oriented instructions
twice, compare results, arbitrate between any differences, then shift workloads "in
flight" to functioning processors, including spares, without any impact to operating systems,
applications, or users. This hardware-level feature, also found in HP's NonStop systems,
is known as lock-stepping, because both processors take their "steps" together. Not all applications
absolutely need the assured integrity that these systems provide, but many do, such as
financial transaction processing. Market
IBM mainframes dominate the mainframe market at well over 90% market share. Unisys manufactures
ClearPath Libra mainframes, based on earlier Burroughs products and ClearPath Dorado mainframes
based on Sperry Univac OS 1100 product lines. In 2002, Hitachi co-developed the zSeries
z800 with IBM to share expenses, but subsequently the two companies have not collaborated on
new Hitachi models. Hewlett-Packard sells its unique NonStop systems, which it acquired
with Tandem Computers and which some analysts classify as mainframes. Groupe Bull's DPS,
Fujitsu BS2000, and Fujitsu-ICL VME mainframes are still available in Europe. Fujitsu, Hitachi,
and NEC still maintain mainframe hardware businesses in the Japanese market.
The amount of vendor investment in mainframe development varies with market share. Fujitsu
and Hitachi both continue to use custom S/390-compatible processors, as well as other CPUs for lower-end
systems. Bull uses a mixture of Itanium and Xeon processors. NEC uses Xeon processors
for its low-end ACOS-2 line, but develops the custom NOAH-6 processor for its high-end
ACOS-4 series. IBM continues to pursue a different business strategy of mainframe investment
and growth. IBM has its own large research and development organization designing new,
homegrown CPUs, including mainframe processors such as 2012's 5.5 GHz six-core zEC12 mainframe
microprocessor. Unisys produces code compatible mainframe systems that range from laptops
to cabinet sized mainframes that utilize homegrown CPUs as well as Xeon processors. IBM is rapidly
expanding its software business, including its mainframe software portfolio, to seek
additional revenue and profits. Furthermore, there exists a market for software
applications to manage the performance of mainframe implementations. In addition to
IBM, significant players in this market include BMC, Compuware, and CA Technologies.
History
Several manufacturers produced mainframe computers from the late 1950s through the 1970s. The
group of manufacturers was first known as "IBM and the Seven Dwarfs": usually Burroughs,
UNIVAC, NCR, Control Data, Honeywell, General Electric and RCA, although some lists varied.
Later, with the departure of General Electric and RCA, it was referred to as IBM and the
BUNCH. IBM's dominance grew out of their 700/7000 series and, later, the development of the
360 series mainframes. The latter architecture has continued to evolve into their current
zSeries mainframes which, along with the then Burroughs and Sperry MCP-based and OS1100
mainframes, are among the few mainframe architectures still extant that can trace their roots to
this early period. While IBM's zSeries can still run 24-bit System/360 code, the 64-bit
zSeries and System z9 CMOS servers have nothing physically in common with the older systems.
Notable manufacturers outside the USA were Siemens and Telefunken in Germany, ICL in
the United Kingdom, Olivetti in Italy, and Fujitsu, Hitachi, Oki, and NEC in Japan. The
Soviet Union and Warsaw Pact countries manufactured close copies of IBM mainframes during the
Cold War; the BESM series and Strela are examples of an independently designed Soviet computer.
Shrinking demand and tough competition started a shakeout in the market in the early 1970s
— RCA sold out to UNIVAC and GE sold its business to Honeywell; in the 1980s Honeywell
was bought out by Bull; UNIVAC became a division of Sperry, which later merged with Burroughs
to form Unisys Corporation in 1986. During the 1980s, minicomputer-based systems
grew more sophisticated and were able to displace the lower-end of the mainframes. These computers,
sometimes called departmental computers were typified by the DEC VAX.
In 1991, AT&T Corporation briefly owned NCR. During the same period, companies found that
servers based on microcomputer designs could be deployed at a fraction of the acquisition
price and offer local users much greater control over their own systems given the IT policies
and practices at that time. Terminals used for interacting with mainframe systems were
gradually replaced by personal computers. Consequently, demand plummeted and new mainframe
installations were restricted mainly to financial services and government. In the early 1990s,
there was a rough consensus among industry analysts that the mainframe was a dying market
as mainframe platforms were increasingly replaced by personal computer networks. InfoWorld's
Stewart Alsop famously predicted that the last mainframe would be unplugged in 1996.
That trend started to turn around in the late 1990s as corporations found new uses for their
existing mainframes and as the price of data networking collapsed in most parts of the
world, encouraging trends toward more centralized computing. The growth of e-business also dramatically
increased the number of back-end transactions processed by mainframe software as well as
the size and throughput of databases. Batch processing, such as billing, became even more
important with the growth of e-business, and mainframes are particularly adept at large
scale batch computing. Another factor currently increasing mainframe use is the development
of the Linux operating system, which arrived on IBM mainframe systems in 1999 and is typically
run in scores or hundreds of virtual machines on a single mainframe. Linux allows users
to take advantage of open source software combined with mainframe hardware RAS. Rapid
expansion and development in emerging markets, particularly People's Republic of China, is
also spurring major mainframe investments to solve exceptionally difficult computing
problems, e.g. providing unified, extremely high volume online transaction processing
databases for 1 billion consumers across multiple industries In late 2000 IBM introduced 64-bit
z/Architecture, acquired numerous software companies such as Cognos and introduced those
software products to the mainframe. IBM's quarterly and annual reports in the 2000s
usually reported increasing mainframe revenues and capacity shipments. However, IBM's mainframe
hardware business has not been immune to the recent overall downturn in the server hardware
market or to model cycle effects. For example, in the 4th quarter of 2009, IBM's System z
hardware revenues decreased by 27% year over year. But MIPS shipments increased 4% per
year over the past two years. In 2012, NASA powered down its last mainframe,
an IBM System z9. Differences from supercomputers
A supercomputer is a computer that is at the frontline of current processing capacity,
particularly speed of calculation. Supercomputers are used for scientific and engineering problems
which are data crunching and number crunching, while mainframes are used for transaction
processing. The differences are as follows: Mainframes are often approximately measured
in millions of instructions per second, but supercomputers are measured in floating point
operations per second and more recently by traversed edges per second or TEPS. Examples
of integer operations include moving data around in memory or checking values. Floating
point operations are mostly addition, subtraction, and multiplication with enough digits of precision
to model continuous phenomena such as weather prediction and nuclear simulations. In terms
of computational ability, supercomputers are more powerful.
Mainframes are built to be reliable for transaction processing as it is commonly understood in
the business world: a commercial exchange of goods, services, or money. A typical transaction,
as defined by the Transaction Processing Performance Council, would include the updating to a database
system for such things as inventory control, airline reservations, or banking. A transaction
could refer to a set of operations including disk read/writes, operating system calls,
or some form of data transfer from one subsystem to another. This operation doesn't count toward
the processing power of a computer. Transaction processing is not exclusive to mainframes
but also used in the performance of microprocessor-based servers and online networks.
In 2007, an amalgamation of the different technologies and architectures for supercomputers
and mainframes has led to the so-called gameframe. See also
Computer types Failover
Gameframe Channel I/O
Cloud computing Notes
References
External links IBM Systems Mainframe Magazine
IBM eServer zSeries mainframe servers Univac 9400, a mainframe from the 1960s, still
in use in a German computer museum Lectures in the History of Computing: Mainframes
Articles and Tutorials at Mainframes360.com: Mainframes
Mainframe Tutorials and Forum at mainframewizard.com: Mainframes