- Mainframes (often colloquially referred to as "big iron" are powerful computers used mainly by large organizations for critical applications, typically bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.
- The term originally referred to the large cabinets 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 firmly established in the 1960s and most large computers were based on architecture established during that era up until the advent of Web servers in the 1990s.
- (The first Web server running anywhere outside Switzerland ran on an IBM mainframe at Stanford University as early as 1991. See History of the World Wide Web for details.)
- There were several minicomputer operating systems and architectures that arose in the 1970s and 1980s, but minicomputers are generally not considered mainframes.
- (UNIX arose as a minicomputer operating system; Unix has scaled up over the years to acquire some mainframe characteristics.)
- Many defining characteristics of "mainframe" were established in the 1960s, but those characteristics continue to expand and evolve to the present day.
and some minicomputers,
- A minicomputer (colloquially, mini) is a class of multi-user computers that lies in the middle range of the computing spectrum, in between the largest multi-user systems (mainframe computers) and the smallest single-user systems (microcomputers or personal computers).
- The class at one time formed a distinct group with its own hardware and operating systems, but the contemporary term for this class of system is midrange computer, such as the higher-end SPARC, POWER and Itanium -based systems from Sun Microsystems, IBM and Hewlett-Packard.
- International Phonetic Alphabet (IPA) using the following transcription, which is not specific to any one dialect.
- To compare these symbols with non-IPA American dictionary conventions you may be more familiar with, see pronunciation respelling for English, which lists the pronunciation guides of fourteen English dictionaries published in the United States.
- If you feel it is necessary to add a pronunciation respelling.
- Computer data storage, often called storage or memory, refers to computer components and recording media that retain digital data used for computing for some interval of time.
- Computer data storage provides one of the core functions of the modern computer, that of information retention.
- It is one of the fundamental components of all modern computers, and coupled with a central processing unit (CPU, a processor), implements the basic computer model used since the 1940s.
- In contemporary usage, memory usually refers to a form of semiconductor storage known as random-access memory, typically DRAM (Dynamic-RAM) but memory can refer to other forms of fast but temporary storage. Similarly, storage today more commonly refers to storage devices and their media not directly accessible by the CPU (secondary or tertiary storage) — typically hard disk drives, optical disc drives, and other devices slower than RAM but more permanent.
- Historically, memory has been called main memory, real storage or internal memory while storage devices have been referred to as secondary storage, external memory or auxiliary/peripheral storage.
Historically, IBM
- International Business Machines (IBM) (NYSE: IBM) is an American multinational technology and consulting firm headquartered in Armonk, New York.
- IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas ranging from mainframe computers to nanotechnology.
- The company was founded in 1911 as the Computing Tabulating Recording Corporation through a merger of four companies: the Tabulating Machine Company, the International Time Recording Company, the Computing Scale Corporation, and the Bundy Manufacturing Company.
- CTR adopted the name International Business Machines in 1924, using a name previously designated to CTR's subsidiary in Canada and later South America.
- Its distinctive culture and product branding has given it the nickname Big Blue.
- disk drives
- magnetic drums
- data cells
IBM mainframes access I/O devices through 'channels', a type of subordinate mini-processor. Channel programs write to, read from, and control the given device.
CTR (CHR)
Channel programs address data through a scheme called module-bin-cyl-trk-rec or MBBCCHHRR, an eight byte address divided into 16 bit-components representing the module and bin (for data cells), cylinder (for discs), head (or track), and the record number. Once the data cell was discontinued[when?], the addressing scheme and the device itself was referred to as CHR or CTR for cylinder-track-record, as the bin number was always 0.
IBM referred to the data records programmers worked with as logical records, and how they were stored on disc as blocks or physical records. One block could contain several logical (or user) records or, in some schemes, partial logical records.
Physical records could have any size up to the limit of a cylinder, although in usual practice, blocks or physical records did not exceed the capacity of a single track.
CKD
CHR/CTR acronyms should not be confused with CKD, which refers to Count Key Data, the layout of an addressable data record on a CTR disc.
FBA
In the 1970s, IBM introduced fixed block architecture, or FBA. At the programming level, these devices did not use the traditional CHR addressing, but referenced fixed-length blocks by number, much like sectors in mini-computers. More correctly, the application programmer remained unaware of the underlying storage arrangement, which stored the data in fixed physical block lengths of 512, 1024, 2048, or 4096.
For many applications, FBA not only offered simplicity, but an increase in throughput. GOAL Systems of Columbus, Ohio, discovered that an FBA emulator written for VM by Bill Jurist delivered an unexpected boost of speed.
Access
The programming interface macros and routines were collectively called[by whom?] DAM: direct access methods.
DOS/VSE
- DAmod/DTFDA – direct access
- SDmod/DTFSD – sequential disc
- ISmod/DTFIS - indexed sequential
- VSAM – virtual sequential access method
VSAM – virtual seqWQuential access method etc.
Present terminology
Both drums and data cells have disappeared as products, so DASD remains as a synonym of a disk device. Modern DASD used in mainframes only very rarely consist of single disk-drives: most commonly "DASD" means large disk arrays utilizing RAID schemes.
- Hard disk
- DFSMS - a standard software managing DASD usage
- ESCON - a protocol for mainframe peripheral communication, used by most DASD devices
- FICON - new protocol to replace ESCON
- IBM Enterprise Storage Server - an example of large DASD
- Global Mirror - DASD remote synchronization product
- Metro Mirror - DASD remote synchronization product
