An IBM 704 mainframe (1964)
Description
Most modern mainframe design is not so much defined by single task computational speed, typically defined as MIPS rate or FLOPS in the case of floating point calculations, as much as by their redundant internal engineering and resulting high reliability and security, extensive input-output facilities, strict backward compatibility with older software, and high hardware and computational utilization rates to support massive throughput. These machines often run for long periods of time without interruption, given their inherent high stability and reliability.
Software upgrades usually require resetting 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(RAS) 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 National Institute of Standards and Technology 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, Linux and Unix.
In the 1960s, most mainframes had no explicitly interactive interface. They accepted sets of punched cards, paper tape, and/or magnetic tape and operated solely in batch mode to support back office functions, such as customer billing. Teletype devices were also common, for system operators, in implementing programming techniques. 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 terminal access for end-users in favour of Web user interfaces.
Historically, mainframes acquired their name in part because of their substantial size, and because of requirements for specialized heating, ventilation, and air conditioning (HVAC), and electrical power, essentially posing a "main framework" of dedicated infrastructure. The requirements of high-infrastructure design were drastically reduced during the mid-1990s with CMOS mainframe designs replacing the olderbipolar technology. IBM claimed that its newer mainframes can reduce data center energy costs for power and cooling, and that they could reduce physical space requirements compared to server farms.
Characteristics
Nearly all mainframes have the ability to run (or host) multiple operating systems, and thereby operate as a host of a collective of virtual machines. 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 are designed to handle very high volume input and output (I/O) and emphasize throughput computing. Since the mid-1960s, mainframe designs have included several subsidiary computers (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 much faster. Other server families also offload I/O processing and emphasize throughput computing.
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 (high-performance computing) which are data crunching and number crunching, while mainframes are used for transaction processing. The differences are as follows:
- Mainframes are measured in millions of instructions per second (MIPS) while assuming typical instructions are integer operations, but supercomputers are measured in floating point operations per second (FLOPS) and more recently by traversed edge 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 (goods), airline reservations (services), or banking (money). 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 does not 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.
- The advantages boil down to redundancy and capacity.
Disadvantages
1.Cost of hardware
2.Special operating systems/software (more cost there, too).
You typically won't see a mainframe used unless some organization with really deep pockets has a mission-critical function that requires massive amounts of information to be processed, in a very reliable manner.Mainframes are computers that are the most bulky types and with the advancement of technology, they have almost become extinct.
Used for the purpose of research, engineering works, meteorological calculations, graphics and the likes, mainframes today constitutes Unix, Linux, and IBM's z/OS, OS/390, MVS, VM, and VSE. Mainframe systems were manufactured extensively throughout the 1950s and were marketed by IBM, Control Data, General Electric, NCR, UNIVAC, Honeywell, RC, and Burroughs.
The three important Features of mainframe Computers:
- Mainframes provide for maximum I/O connectivity as they accommodate huge disc farms.
- Mainframes excel in providing maximum I/O band width. Interestingly in spite of all the connected drives connected to the mainframe system, no data blocking ever happens to mar its efficiency.
- Mainframe systems also provide for very good single thread operations.
