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63-473: Access to computer systems for many years consisted of connecting a terminal to a mainframe system via a serial line and the RS-232 protocol . When a system of software interrupts , called signals, was being developed, one of those signals was designated for use on hangup. SIGHUP would be sent to programs when the serial line was dropped, often because the connected user terminated the connection by hanging up

126-448: A deadlock occurs, and neither transaction can move forward. Transaction-processing systems are designed to detect these deadlocks when they occur. Typically both transactions will be cancelled and rolled back, and then they will be started again in a different order, automatically, so that the deadlock does not occur again. Or sometimes, just one of the deadlocked transactions will be cancelled, rolled back, and automatically restarted after

189-512: A function , ignoring it, or restoring the default action. The default action on POSIX -compliant systems is an abnormal termination. Mainframe computer A mainframe computer , informally called a mainframe or big iron , is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses , industry and consumer statistics , enterprise resource planning , and large-scale transaction processing . A mainframe computer

252-531: A main frame , that housed the central processing unit and main memory of early computers. Later, the term mainframe was used to distinguish high-end commercial computers from less powerful machines. Modern mainframe design is characterized less by raw computational speed and more by: The high stability and reliability of mainframes enable these machines to run uninterrupted for very long periods of time, with mean time between failures (MTBF) measured in decades. Mainframes have high availability , one of

315-413: A book from an online bookstore, you exchange money (in the form of credit ) for a book. If your credit is good, a series of related operations ensures that you get the book and the bookstore gets your money. However, if a single operation in the series fails during the exchange, the entire exchange fails. You do not get the book and the bookstore does not get your money. The technology responsible for making

378-408: A configuration file that has been changed. Symbolic signal names are used because signal numbers can vary across platforms, but XSI -conformant systems allow the use of the numeric constant 1 to be used to indicate a SIGHUP, which the vast majority of systems in fact use. SIGHUP can be handled . That is, programmers can define the action they want to occur upon receiving a SIGHUP, such as calling

441-407: A controlling terminal, such as daemons , would re-purpose SIGHUP as a signal to re-read configuration files , or reinitialize. This convention survives to this day in packages such as Apache and Sendmail . With the decline of access via serial line, the meaning of SIGHUP has changed somewhat on modern systems, often meaning a controlling pseudo or virtual terminal has been closed. If a command

504-427: A database management system. (sometimes called after images ). This is not required for rollback of failed transactions but it is useful for updating the database management system in the event of a database failure, so some transaction-processing systems provide it. If the database management system fails entirely, it must be restored from the most recent back-up. The back-up will not reflect transactions committed since

567-449: 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

630-539: A level of sophistication not usually available with most server solutions. Modern mainframes, notably the IBM Z servers, offer two levels of virtualization : logical partitions ( LPARs , via the PR/SM facility) and virtual machines (via the z/VM operating system). 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

693-434: A reference to the anticipated Year 2000 problem (Y2K). 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

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756-428: A short delay. Deadlocks can also occur among three or more transactions. The more transactions involved, the more difficult they are to detect, to the point that transaction processing systems find there is a practical limit to the deadlocks they can detect. In systems where commit and rollback mechanisms are not available or undesirable, a compensating transaction is often used to undo failed transactions and restore

819-407: 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

882-412: A single, indivisible transaction, and ensures that either all operations in a transaction are completed without error, or none of them are. If some of the operations are completed but errors occur when the others are attempted, the transaction-processing system "rolls back" all of the operations of the transaction (including the successful ones), thereby erasing all traces of the transaction and restoring

945-400: A transaction partially completed. If the computer system crashes in the middle of a transaction, the transaction processing system guarantees that all operations in any uncommitted transactions are cancelled. Generally, transactions are issued concurrently. If they overlap (i.e. need to touch the same portion of the database), this can create conflicts. For example, if the customer mentioned in

1008-430: A transaction-oriented application that performs the routine transactions necessary to conduct business. Examples include systems that manage sales order entry, airline reservations, payroll, employee records, manufacturing, and shipping. Since most, though not necessarily all, transaction processing today is interactive, the term is often treated as synonymous with online transaction processing . Transaction processing

1071-732: 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 (in IBM's case), or with shared, geographically dispersed storage provided by EMC or Hitachi. Mainframes are designed to handle very high volume input and output (I/O) and emphasize throughput computing. Since

1134-450: 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 (banking, insurance, credit reporting, government services, etc.) In late 2000, IBM introduced 64-bit z/Architecture , acquired numerous software companies such as Cognos and introduced those software products to

1197-634: Is being refreshed. In the late 1950s, mainframes had only a rudimentary interactive interface (the console) and used 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 payroll and customer billing, most of which were based on repeated tape-based sorting and merging operations followed by line printing to preprinted continuous stationery . When interactive user terminals were introduced, they were used almost exclusively for applications (e.g. airline booking ) rather than program development. However, in 1961

1260-757: 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 (through instruction retry and failure isolation), 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,

1323-488: Is designed to maintain a system's Integrity (typically a database or some modern filesystems ) in a known, consistent state, by ensuring that interdependent operations on the system are either all completed successfully or all canceled successfully. For example, consider a typical banking transaction that involves moving $ 700 from a customer's savings account to a customer's checking account. This transaction involves at least two separate operations in computer terms: debiting

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1386-410: Is executed inside a terminal window and the terminal window is closed while the command process is still running, it receives SIGHUP. If the process receiving SIGHUP is a Unix shell , then as part of job control it will often intercept the signal and ensure that all stopped processes are continued before sending the signal to child processes (more precisely, process groups , represented internally by

1449-421: Is known as lock-stepping, because both processors take their "steps" (i.e. instructions) together. Not all applications absolutely need the assured integrity that these systems provide, but many do, such as financial transaction processing. IBM , with the IBM Z series, continues to be a major manufacturer in the mainframe market. In 2000, Hitachi co-developed the zSeries z900 with IBM to share expenses, and

1512-412: Is large but not as large as a supercomputer and has more processing power than some other classes of computers, such as minicomputers , servers , workstations , and personal computers . 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

1575-641: Is the X/Open Distributed Transaction Processing (DTP) (see also Java Transaction API (JTA). However, proprietary transaction-processing environments such as IBM's CICS are still very popular, although CICS has evolved to include open industry standards as well. The term extreme transaction processing (XTP) was used to describe transaction processing systems with uncommonly challenging requirements, particularly throughput requirements (transactions per second). Such systems may be implemented via distributed or cluster style architectures. It

1638-493: The Telum . Unisys produces code compatible mainframe systems that range from laptops to cabinet-sized mainframes that use homegrown CPUs as well as Xeon processors. Furthermore, there exists a market for software applications to manage the performance of mainframe implementations. In addition to IBM, significant market competitors include BMC and Precisely ; former competitors include Compuware and CA Technologies . Starting in

1701-485: The Web ), a single distributed database was not a practical solution. In addition, most online systems consist of a whole suite of programs operating together, as opposed to a strict client–server model where the single server could handle the transaction processing. Today a number of transaction processing systems are available that work at the inter-program level and which scale to large systems, including mainframes . One effort

1764-433: The modem . The system would detect the line was dropped via the lost Data Carrier Detect (DCD) signal. Signals have always been a convenient method of inter-process communication (IPC), but in early implementations there were no user-definable signals (such as the later additions of SIGUSR1 and SIGUSR2 ) that programs could intercept and interpret for their own purposes. For this reason, applications that did not require

1827-504: The 1980s, many mainframes supported general purpose graphic display terminals, and terminal emulation, but not graphical user interfaces. This form of end-user computing became obsolete in the 1990s due to the advent of personal computers provided with GUIs . After 2000, modern mainframes partially or entirely phased out classic " green screen " and color display terminal access for end-users in favour of Web-style user interfaces. The infrastructure requirements were drastically reduced during

1890-595: The 2010s, cloud computing is now a less expensive, more scalable alternative. Several manufacturers and their successors produced mainframe computers from the 1950s until the early 21st century, with gradually decreasing numbers and a gradual transition to simulation on Intel chips rather than proprietary hardware. The US 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

1953-890: The 64-bit IBM Z CMOS servers have nothing physically in common with the older systems. Notable manufacturers outside the US 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 independently designed Soviet computers. Elwro in Poland

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2016-542: 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 (including POWER and Xeon) 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 also develops custom processors in-house, such as

2079-524: The back-office engines behind the world's financial markets and much of global commerce". As of 2010 , while mainframe technology represented less than 3% of IBM's revenues, it "continue[d] to play an outsized role in Big Blue's results". IBM has continued to launch new generations of mainframes: the IBM z13 in 2015, the z14 in 2017, the z15 in 2019, and the z16 in 2022, the latter featuring among other things an "integrated on-chip AI accelerator" and

2142-403: The back-up was made. However, once the database management system is restored, the journal of after images can be applied to the database ( rollforward ) to bring the database management system up to date. Any transactions in progress at the time of the failure can then be rolled back. The result is a database in a consistent, known state that includes the results of all transactions committed up to

2205-415: The database prior to its modification by a transaction are set aside by the system before the transaction can make any modifications (this is sometimes called a before image ). If any part of the transaction fails before it is committed, these copies are used to restore the database to the state it was in before the transaction began. It is also possible to keep a separate journal of all modifications to

2268-592: 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 (now Unisys ) 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,

2331-440: The different technologies and architectures for supercomputers and mainframes has led to a so-called gameframe . Transaction processing In computer science , transaction processing is information processing that is divided into individual, indivisible operations called transactions . Each transaction must succeed or fail as a complete unit; it can never be only partially complete. For example, when you purchase

2394-558: The early 1990s, many supercomputers were based on a mainframe architecture with supercomputing extensions. An example of such a system is the HITAC S-3800 , which was instruction-set compatible with IBM System/370 mainframes, and could run the Hitachi VOS3 operating system (a fork of IBM MVS ). The S-3800 therefore can be seen as being both simultaneously a supercomputer and also an IBM-compatible mainframe. In 2007, an amalgamation of

2457-411: The example above has $ 150 in his savings account and attempts to transfer $ 100 to a different person while at the same time moving $ 100 to the checking account, only one of them can succeed. However, forcing transactions to be processed sequentially is inefficient. Therefore, concurrent implementations of transaction processing is programmed to guarantee that the end result reflects a conflict-free outcome,

2520-488: The exchange balanced and predictable is called transaction processing . Transactions ensure that data-oriented resources are not permanently updated unless all operations within the transactional unit complete successfully. By combining a set of related operations into a unit that either completely succeeds or completely fails, one can simplify error recovery and make one's application more reliable. Transaction processing systems consist of computer hardware and software hosting

2583-748: The first academic, general-purpose timesharing system that supported software development, CTSS , was released at MIT on an IBM 709 , later 7090 and 7094. Typewriter and Teletype devices were common control consoles for system operators through the early 1970s, although ultimately supplanted by keyboard / display devices. By the early 1970s, many mainframes acquired interactive user terminals operating as timesharing computers, supporting hundreds of users simultaneously along with batch processing. Users gained access through keyboard/typewriter terminals and later character-mode text terminal CRT displays with integral keyboards, or finally from personal computers equipped with terminal emulation software. By

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2646-559: The first time. IBM received the vast majority of mainframe revenue. 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 Digital Equipment Corporation VAX series. In 1991, AT&T Corporation briefly owned NCR. During the same period, companies found that servers based on microcomputer designs could be deployed at

2709-492: The job table but prevents them from receiving SIGHUP on shell termination. Different shells also have other methods of controlling and managing SIGHUP, such as the disown facility of ksh . Most modern Linux distributions documentation specify using kill -HUP <processID> to send the SIGHUP signal. Daemon programs sometimes use SIGHUP as a signal to restart themselves, the most common reason for this being to re-read

2772-752: The late 1950s, mainframe designs have included subsidiary hardware (called channels or peripheral processors ) 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 reasonably quickly. Other server families also offload I/O processing and emphasize throughput computing. Mainframe return on investment (ROI), like any other computing platform,

2835-726: The latest Hitachi AP10000 models are made by IBM. Unisys manufactures ClearPath Libra mainframes, based on earlier Burroughs MCP products and ClearPath Dorado mainframes based on Sperry Univac OS 1100 product lines. Hewlett Packard Enterprise sells its unique NonStop systems, which it acquired with Tandem Computers and which some analysts classify as mainframes. Groupe Bull 's GCOS , Stratus OpenVOS , Fujitsu (formerly Siemens) BS2000 , and Fujitsu- ICL VME mainframes are still available in Europe, and Fujitsu (formerly Amdahl) GS21 mainframes globally. NEC with ACOS and Hitachi with AP10000- VOS3 still maintain mainframe businesses in

2898-477: 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 (millions of instructions per second) shipments increased 4% per year over

2961-472: The mid-1990s, when CMOS mainframe designs replaced the older bipolar technology. IBM claimed that its newer mainframes reduced data center energy costs for power and cooling, and reduced physical space requirements compared to server farms . 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,

3024-456: The moment of failure. In some cases, two transactions may, in the course of their processing, attempt to access the same portion of a database at the same time, in a way that prevents them from proceeding. For example, transaction A may access portion X of the database, and transaction B may access portion Y of the database. If at that point, transaction A then tries to access portion Y of the database while transaction B tries to access portion X,

3087-433: The most secure, with vulnerabilities in the low single digits, as compared to thousands for Windows , UNIX , and Linux . Software upgrades usually require setting up the operating system or portions thereof, and are non disruptive only when using virtualizing facilities such as IBM z/OS and Parallel Sysplex , or Unisys XPCL, which support workload sharing so that one system can take over another's application while it

3150-431: The new Telum microprocessor . A supercomputer is a computer at the leading edge of data processing capability, with respect to calculation speed. Supercomputers are used for scientific and engineering problems ( high-performance computing ) which crunch numbers and data, while mainframes focus on transaction processing. The differences are: Mainframes and supercomputers cannot always be clearly distinguished; up until

3213-433: The past two years. Alsop had himself photographed in 2000, symbolically eating his own words ("death to the mainframe"). In 2012, NASA powered down its last mainframe, an IBM System z9. However, IBM's successor to the z9, the z10 , led a New York Times reporter to state four years earlier that "mainframe technology—hardware, software and services—remains a large and lucrative business for I.B.M., and mainframes are still

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3276-628: 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 serviceability (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 vulnerabilities database, US-CERT , rates traditional mainframes such as IBM Z (previously called z Systems, System z, and zSeries), Unisys Dorado, and Unisys Libra as among

3339-400: The same as could be reached if executing the transactions sequentially in any order (a property called serializability ). In our example, this means that no matter which transaction was issued first, either the transfer to a different person or the move to the checking account succeeds, while the other one fails. The basic principles of all transaction-processing systems are the same. However,

3402-416: The savings account by $ 700, and crediting the checking account by $ 700. If one operation succeeds but the other does not, the books of the bank will not balance at the end of the day. There must, therefore, be a way to ensure that either both operations succeed or both fail so that there is never any inconsistency in the bank's database as a whole. Transaction processing links multiple individual operations in

3465-547: The shell as a "job"), which by default terminates them. This can be circumvented in two ways. Firstly, the Single UNIX Specification describes a shell utility called nohup , which can be used as a wrapper to start a program and make it ignore SIGHUP by default. Secondly, child process groups can be "disowned" by invoking disown with the job id , which removes the process group from the shell's job table (so they will not be sent SIGHUP), or (optionally) keeps them in

3528-613: The size and throughput of databases. Batch processing, such as billing, became even more important (and larger) 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. 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 ,

3591-479: The state. The actions taken as a group do not violate any of the integrity constraints associated with the state. Even though transactions execute concurrently, it appears to each transaction T, that others executed either before T or after T, but not both. Once a transaction completes successfully (commits), its changes to the database survive failures and retain its changes. Standard transaction-processing software , such as IBM 's Information Management System ,

3654-416: The system to a previous state. Jim Gray defined properties of a reliable transaction system in the late 1970s under the acronym ACID —atomicity, consistency, isolation, and durability. A transaction's changes to the state are atomic: either all happen or none happen. These changes include database changes, messages, and actions on transducers. Consistency : A transaction is a correct transformation of

3717-405: The system to the consistent, known state that it was in before processing of the transaction began. If all operations of a transaction are completed successfully, the transaction is committed by the system, and all changes to the database are made permanent; the transaction cannot be rolled back once this is done. Transaction processing guards against hardware and software errors that might leave

3780-400: The terminology may vary from one transaction-processing system to another, and the terms used below are not necessarily universal. Transaction-processing systems ensure database integrity by recording intermediate states of the database as it is modified, then using these records to restore the database to a known state if a transaction cannot be committed. For example, copies of information on

3843-410: 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 infamously predicted that the last mainframe would be unplugged in 1996; in 1993, he cited Cheryl Currid, a computer industry analyst as saying that the last mainframe "will stop working on December 31, 1999",

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3906-569: Was another Eastern Bloc manufacturer, producing the ODRA , R-32 and R-34 mainframes. 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; between 1986 and 1990 Honeywell was bought out by Bull ; UNIVAC became a division of Sperry , which later merged with Burroughs to form Unisys Corporation in 1986. In 1984 estimated sales of desktop computers ($ 11.6 billion) exceeded mainframe computers ($ 11.4 billion) for

3969-404: Was first developed in the 1960s, and was often closely coupled to particular database management systems . Client–server computing implemented similar principles in the 1980s with mixed success. However, in more recent years, the distributed client–server model has become considerably more difficult to maintain. As the number of transactions grew in response to various online services (especially

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