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A mainframe computer, informally called a mainframe or big iron, [1] 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.
IBM mainframes are large computer systems produced by IBM since 1952. During the 1960s and 1970s, IBM dominated the computer market with the 7000 series and the later System/360, followed by the System/370. Current mainframe computers in IBM's line of business computers are developments of the basic design of the System/360.
It is a complete protocol stack for interconnecting computers and their resources. SNA describes formats and protocols but, in itself, is not a piece of software. The implementation of SNA takes the form of various communications packages, most notably Virtual Telecommunications Access Method (VTAM), the mainframe software package for SNA ...
Similarly to the mainframe version of VM/CMS, the VM/PC also created the illusion of virtual disks, but on the PC version these were maintained as PC DOS files, either on floppy or hard disk. For example, the CMS virtual disk belonging to user FRED at device address 101 was stored as the DOS file FRED.101.
The first use of channel I/O was with the IBM 709 [2] vacuum tube mainframe in 1957, whose Model 766 Data Synchronizer was the first channel controller. The 709's transistorized successor, the IBM 7090, [3] had two to eight 6-bit channels (the 7607) and a channel multiplexor (the 7606) which could control up to eight channels.
IBM System z9 is a line of IBM mainframe computers. The first models were available on September 16, 2005. The System z9 also marks the end of the previously used eServer zSeries naming convention. It was also the last mainframe computer that NASA ever used. [1]
These were identified as BG (background), F1 (foreground 1) and F2 (foreground 2). Multiprogramming was an optional feature of DOS/360, selectable at system generation. [23]: p.34 A later SYSGEN option allowed batch operation run in either FG partition. Otherwise foreground programs had to be manually started by the computer operator.
The main machine in the line was the GE-225 (1961). [5] [3] It used a 20-bit word, of which 13 bits could be used for an address.Along with the basic central processing unit (CPU) the system could also have had a floating-point unit (the "Auxiliary Arithmetic Unit"), or a fixed-point decimal option with three six-bit decimal digits per word.