IBM System/370 Model 125

IBM System/370 Model 125

IBM System/370 Model 125
Announced Oct 4, 1972 and
withdrawn Mar 9, 1981
The following is the text of an IBM Data Processing Division technical press release distributed on October 4, 1972.

The IBM System/370 Model 125, announced today, makes it easier and more economical than ever for many computer users to move into the key data processing applications of the Seventies.

Such advanced applications as on-line data entry and inquiry and remote computing can benefit from the Model 125's virtual storage, large-capacity direct-access storage, high processing speeds and data communication capabilities.

Up to 400 million bytes on-line

The IBM 3333 disk storage unit attaches directly to the Model 125 via an integrated disk attachment, eliminating the need for - - and cost of - - a separate data channel or control unit. A user can have either two, three or four disk drives, each with 100 million bytes of storage capacity.

Below is a comparison of the IBM 3330-series, 2311 and 2314-series disk devices:

IBM 3330-series IBM 2314-series IBM 2311 (Model 1)
Data capacity (bytes-per-disk-pack) 100 million 29.7 million 7.25 million
Average access time (milliseconds) 30 60 75
Maximum data rate (bytes-per-second) 806,000 312,000 156,000

An operator's console that incorporates a cathode ray tube can display data entered through the console keyboard, the contents of storage and internal registers, and information from the disk files. It can display up to 16 lines of data, with 56 characters per line. An optional stand-alone console printer can provide hard copy of the CRT displays, at the rate of 85 characters per second.

Advanced processor design

The Model 125's central processor consists of a main storage facility surrounded by independent "satellite" subprocessors, all contained within the computer mainframe. These distributed subprocessors, each having its own data storage and logic, provide for independent handling of program instructions input/output functions, and system diagnostics.

Because each of the subprocessors has its own data path to the system's main storage, interference and contention between the various processing elements for access to main storage are reduced. This helps improve overall system performance. The independent subprocessor design also incorporates the integrated features that allow a variety of peripheral devices to be attached directly to the Model 125.

Integrated I/O capabilities

An optional integrated magnetic tape adapter enables the Model 125 to operate with the IBM 3410/3411 magnetic tape subsystem. Up to six tape drives can be included in a subsystem, with data rates of 20,000 (four-drive maximum), 40,000 or 80,000 bytes-per-second available to meet specific user requirements.

Up to 22 data communications lines also can be optionally attached to the Model 125, via an integrated communications adapter. This feature supports up to 16 start/stop lines and up to six bi-synchronous lines to connect a wide range of IBM terminal devices to the central computer. With such a network, the Model 125's data base and processing capabilities become economically available to a user's remotely located facilities.

For data handling versatility, the Model 125 can read and punch both traditional 80-column cards or the newer 96-column cards used with the IBM System/3. For 80-column cards, the new IBM 3504 card reader attaches directly to the Model 125 to offer read speeds of either 800 or 1,200 cards-a-minute and an optional optical mark reading capability. The IBM 3525 card punch can be added to provide punching speeds of either 100, 200 or 300 cards per minute. Optional features provide multiple line printing.

The Model 125 also can use a variety of other IBM devices to process 80-column cards, including the 2560 multi-function card machine used with System /360 Model 20. A new 5425 multi-function card unit can be directly attached to process 96-column cards, permitting data to be exchanged with System /3.

An integrated printer attachment enables the Model 125 to use an IBM 1403 printer, with speeds of 600 to 1,100 lines-per-minute. In addition, the Model 125 users can select an optional byte multiplexer channel that permits use of a wide variety of other peripheral devices, including the IBM 3881 optical mark reader and IBM 3270 information display system.

Main storage technology

Main storage capacities of 98,304 and 131,072 bytes are available with the Model 125. High density monolithic MOSFET (metal oxide semiconductor field-effect transistor) technology is used for the Model 125's main and control storage circuits. Recently introduced with IBM's larger-scale System/370 Models 158 and 168, MOSFET main storage is much more compact and handles data faster than ferrite core storage used in many computers. The Model 125's main storage basic cycle time is 480 nanoseconds for two bytes of data, almost twice as fast as the core memory of the Model 25.

In addition to its main storage, the Model 125 also provides a standard 12,288 words (22-bit words) of reloadable control storage, expandable by increments of 4,096 to a maximum of 20,480 words. Reloadable control storage relieves main storage from many tasks by holding the microcode required to help run emulation programs, monitor system performance, and execute on-line diagnostics and other important system-related functions. It is loaded from a magnetic disk cartridge that makes it easier to add features to the system.

Prices & availability

Shipments of the IBM System/370 Model 125 will be scheduled to begin in April 1973. Typical monthly rental will range from $8,207 to $13,794 with purchase prices ranging from $377,815 to $602,620. The recently announced DOS/VS, fully supporting the Model 125's virtual storage capability, is scheduled to become available in June 1973. The Model 125 will be manufactured at IBM facilities in Poughkeepsie, New York; Vimercate, Italy and Yasu, Japan. Much of the development work was done at the IBM laboratories in Boeblingen, Germany.