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Announced Aug 2, 1972 and
withdrawn Sep 15, 1980The IBM System/370 Model 158 was a medium-size, high performance data processing system that incorporated integrated monolithic main storage, virtual storage capability, integrated storage controls, and a display console. These functional capabilities made possible expanded applications for large-scale users.

The basic components of the System/370 Model 158 were the IBM 3158 Processing Unit, the display console, and an optional console printer. A large number and variety of storage and communication devices could be attached.

General upward compatibility with most System/360 architecture and programming was maintained through implementation of the basic control (BC) mode of system operation. An extended control (EC) mode of operation was also supported. When the Model 158 operated in EC mode, the program status word (PSW) format and the layout of permanently assigned lower processor storage were altered to support additional system control and functions, such as dynamic address translation.

• Dynamic address translation (DAT) hardware was standard. Operating only in EC mode, it provided translation of virtual storage addresses into real storage addresses during program execution.

• The virtual storage concept could be extended to direct access devices and volumes by using the optional 3850 Mass Storage System.

• Channel indirect data addressing was a standard feature that was used when operating in EC mode. Because an I/O buffer could be assigned to noncontiguous real storage areas, channel indirect data addressing was required to access a list of the real storage areas (page frames) assigned.

• Monolithic processor (main) storage of up to four megabytes was available in a single Model 158.

• Standard high-speed buffer storage was 8K on Model 1, and 16K on Model 3.

• Instructions were provided on the MP models to support a Model 158 tightly coupled multiprocessing system.

• The display console provided a communication link between the operator and the entire system. The console used a CRT display, a keyboard, and a light pen. A console printer (up to 85 characters per second) to provide hard copy was optional when the console was in display mode, and required when it was in printer-keyboard mode. Most switch, pushbutton, and indicator functions were replaced by CRT displays.

• The optional Power Warning feature provided a machine check interrupt when a power line disturbance beyond certain limits was signaled to the CPU by a customer-provided Uninterruptible Power Supply (UPS) and sensor supporting the system.

• Integrated emulators supported the concurrent execution of System/370 programs with 7070/7074, 1401/1440/1460, and 1410/7010 programs in a multiprogramming environment.

• An OS/DOS Compatibility feature was optional, at no charge, and an OS/DOS emulator program was available. The emulator feature and companion program provided for the execution of a DOS supervisor and DOS programs under OS control.

• An interval timer of 3.33 ms was provided for job accounting.

• A Clock Comparator and a CPU Timer were standard. The CPU Timer provided an interval timing capability equivalent to that of the interval timer but with a resolution equal to that of the time-of-day clock. The Clock Comparator could be used to cause an interrupt when the time-of-day clock reached a specified value. The CPU Timer and the Clock Comparator provided higher-resolution, timing than the standard interval timer. Additional instructions controlled the system timing facilities.

• A time-of-day clock that was updated every usec was included to provide time-of-day values in conjunction with available programming support.

• A monitor function was standard and could be used to trace user-defined program events for debugging or gathering statistics.

• Extended precision floating point was available to provide precision of up to 28 hexadecimal digits, equal to up to 34 decimal digits.

• Byte (as opposed to word or doubleword) boundary alignment was permitted for the operands of nonprivileged instructions to reduce the need for padding bytes in records for the purpose of aligning fixed or floating point data.

• An optional channel-to-channel adapter could be used to interconnect two channels, either System/360 or System/370. This adapter was used to link the processing units in a loosely coupled multiprocessing system.