IBM System/370 Model 155

IBM System/370 Model 155

IBM System/370 Model 155
Announced Jun 30, 1970 and
withdrawn Dec 23, 1977
The IBM System/370 Model 155 was a high-performance data processing system that provided the reliability, availability, and convenience demanded by business and scientific users, as well as by users with applications in communications or control.

The Model 155 included the advantages, characteristics, and functions pioneered by the IBM System/360. The high performance of the Model 155 can be attributed to:

Programming support for the System/370 Model 155 was provided by System/360 Operating System (OS), MFT and MVT, as well as System/360 Disk Operating System (DOS). The Model 155 took advantage of the gains possible because of this support.

The Model 155 had a major machine cycle time of 115 nanoseconds. Main-storage data flow was 16 bytes (one quadword). Main-storage cycle time was 2.07 microseconds. However, the high-speed buffer storage operated to make the effective system storage cycle time one-third to one-quarter of the actual main-storage cycle time.

Seven capacities of main storage were available, with error checking and correction (ECC) implemented in the processor storage units.

For input/output operations, the system could have one byte multiplexer channel and as many as five block multiplexer channels, or two byte multiplexer channels and as many as four block multiplexer channels.

System components

The major components in a System/370 Model 155 were the IBM 3155 Processing Unit, which contained arithmetic and logical circuits, read-only storage, local storage, and at least three input/output channels; and the IBM 3360 Processor Storage. Input/output devices were attached to the channels by control units.

Standard features

The standard features for any IBM 3155 Processing Unit included:

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