A mainframe computer, informally called a mainframe, maxicomputer, 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 is large but not as large as a supercomputer and has more processing power than some other classes of computers, such as minicomputers, 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 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.
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 with older software High hardware and computational utilization rates through virtualization to support massive throughput Hot swapping of hardware, such as processors and memory
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 the primary reasons for their longevity, since they are typically used in applications where downtime would be costly or catastrophic. High levels of reliability, availability and serviceability (RAS) is a defining characteristic of mainframe computers. 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 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 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 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 terminalsSome had been introduced in the 1960s, but their deployment became more common in the 1970s operating as timesharing computers, supporting hundreds of users simultaneously along with batch processing. Users gained access through keyboard/typewriter terminals and later character-mode textGraphics terminals were available but tended to be restricted to niche applications. terminal cathode-ray tube displays with integral keyboards, or finally from personal computers equipped with terminal emulation software. By 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 graphical user interfaces. 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 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.
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 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 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 the late 1950s,E.g., the IBM 709 had channels in 1958. mainframe designs have included subsidiary hardwareSometimes computers, sometimes more limited. (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, 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, 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.
Mainframe audit A mainframe audit is a comprehensive inspection of computer processes, security, and procedures, with recommendations for improvement.
Organizations in different industries have different auditing and security requirements. Some factors affecting the organizations' requirements are: regulatory requirements and other external factors; management, objectives, and business practices; and the organizations' performance compared to the industry. This information can be obtained by conducting outside research, interviewing employees, touring the data center and observing activities, consultations with technical experts, and looking at company manuals and business plans. Another consideration is the level of mainframe access employees have and if password policies are in place and followed. Evidence of implementation can be obtained by requesting employee manuals, evaluating the software and user histories, and by physical observation of the environment.Gallegos, F., Senft, S., Manson, D., Gonzales, C. (2004). Information Technology Control and Audit. (2nd ed.) Boca Raton, Florida: Auerbach Publications. Physical access is also an area of interest. Are cables adequately protected from damage and sniffing between the Network and the Data Center? This can be achieved by proper routing of the cables, encryption, and a good network topology. Physical observation of where the cables are routed and confirmation of the security procedures should be obtained. Tests of controls should be conducted to determine any additional weaknesses. Does the mainframe have access to an adequate uninterruptible power supply? Are physical controls such as power badges for access, fire suppression devices, and locks in place to protect the data center (and the mainframe inside) from theft, manipulation or damage? Physical observation is necessary to ensure these requirements.
An operating system is usually designed with the following considerations:
There must be controls in place to ensure the software is continually updated. Is the software configured to do updates, or is it done by the system technicians? Controls should be in place to deter unauthorized manipulation or theft of data. Proper separation of duties also needs to be verified. The company’s internal controls need to be tested to determine if they are effective. Samples of entries into the system should be examined to verify that the controls are effective, while unauthorized and suspicious voided transactions need to be investigated. There must not be any processes on the system that could needlessly compromise other components. Procedures and measures need to be in place to minimize the risk of unauthorized access through Backdoors in the system, such as the Program Properties Table (PPT). There should be an accurate audit trail that can be followed.The Henderson Group (October, 2001) Mainframe Audit News: Issue no.1. Also issues 2, 3 and 4 from the same source. Retrieved January 27, 2006.
Security audits usually have the following considerations:
Are proper separation of duties implemented and enforced, and are technology and procedures in place to make sure there is a continuous and accurate audit trail? Controls need to be put in place to minimize the risk of unnecessary and unauthorized entry into the system, and the protection of passwords. Computer-assisted audit techniques should be used to scan the system (continuous monitoring is ideal), with human observations conducted to verify procedures, such as to verify that protocols like separation of duties are being followed.