IBM System/370 Model 165

IBM System/370 Model 165

IBM System/370 Model 165
Announced Jun 30, 1970 and
withdrawn Dec 23, 1977
The following are excerpts from an IBM Data Processing Division press technical fact sheet distributed on June 30, 1970.

IBM System/370 Models 155 and 165, announced today, are designed for the emerging data processing needs of the Seventies - - large data bases, remote computing and high-throughput multiprogramming.

In designing System/370, IBM engineers used many advanced concepts found previously only in the company's most powerful computers. They make it possible for medium- and large-scale computer users to achieve vastly higher performance and storage capacity per data processing dollar.

System/370 users - - both business and scientific - - will be able to run their System/360 applications on the new system with little or no program modification. The majority of current IBM input and output devices can operate with System/370. Both models run under proven OS programming support. In addition, Model 155 will run under DOS support. The basic architecture of System/360, introduced in 1964, has been extended, but not redesigned, for System/370.

Both models of the system - - which are compatible with each other - - stress balanced performance, combining high internal operating speed with an advanced memory hierarchy, expanded data channels, new high-capacity disk storage and printing at 2,000 lines a minute.

The Model 155 offers medium-scale users vastly higher data processing power at prices until now associated with machines having far less capability. System/360 Model 40 and 50 users will find the System/370 Model 155 particularly attractive as a growth computer. The more powerful Model 165 offers significantly expanded facilities to Model 65 and 75 users without parallel cost increases.

Circuit technology

System/370 uses highly reliable monolithic integrated circuits for arithmetic and logic functions. Monolithics also are used as storage devices in the high-speed buffer memory. Central processing units of both the Models 155 and 165 use the IBM Monolithic Systems Technology (MST). The monolithic chips used in the Model 155, for example, are 80 mils (thousandths of an inch) square, operate at speeds ranging from 6 to 8 nanoseconds (billionths of a second) and contain from two to eight complete circuits.

The high-performance buffer memory uses chips 112 mils square, each containing 64 microscopic memory circuits that operate in 80 nanoseconds in the Model 165 and 115 nanoseconds in the Model 155. The chip also contains eight driver circuits. A single chip can integrate the equivalent of 664 transistors, diodes and other circuit components.

The packaging techniques for both MST and buffer memory circuits in System/370 are evolutionary extensions of IBM Solid Logic Technology (SLT) used in most models of System/360. Many chip fabricating techniques are similar, including silicon crystal growth, diffusion processes and photochemical etching. The chips are placed on a ceramic substrate and encapsulated in half-inch-square modules.

Memory hierarchy

Both Models 155 and 165 have two-level memory systems - - a very high-performance buffer storage backed by a large main core storage. This hierarchy, in which the CPU gets data directly from the faster buffer most of the time, significantly reduces the effective main storage cycle and closely matches the memory cycle to CPU cycle. (Model 165 main storage has a 2-microsecond cycle and its buffer storage has an 80-nanosecond cycle. The Model 155 main storage has a 2.1-microsecond cycle while its buffer has a 115-nanosecond cycle. In operation, the 155 accesses four bytes in two cycles -- 230 nanoseconds. A byte is a unit of storage equivalent to a character or two decimal digits.)

The buffer memory holds large blocks of data and instructions ready for use by the CPU. It operates automatically, requires no special programming and is "transparent" to the user. The user perceives only that the computer performs as if the large capacity main storage is much faster than its rated cycle speed.

Users of the Model 165 will have a choice of five main core storage sizes, ranging from 512,000 to over 3-million bytes. Seven main memory sizes are available for the Model 155, ranging from 256,000 to over 2-million bytes.

Two buffer memory sizes - - 8,000 and 16,000 bytes - - are available with the Model 165, while an 8,000-byte buffer is standard with Model 155.


Channels - - the data paths that link memory and all system devices to the CPU -- have been greatly expanded in System/370, both in number and data rate. The maximum of 12 channels available for the Model 165 can provide a total data rate of more than 8-million bytes a second - - twice the rate of System/360 Model 65.

The increased data rates and number of channels available for System/370 will permit users to further expand their multiprogramming operations, and take advantage of new, higher speed disk storage for data base applications.

Both Models 155 and 165 can use block multiplexing channels, previously available only with System/360 Models 85 and 195 - - IBM's most powerful computers. Block multiplexing is a technique that allows simultaneous execution of multiple high-speed channel programs, thereby increasing system throughput. For example, multiple high-speed input and output devices, such as the IBM 3330 and 2305 disk storage devices, can operate concurrently, sharing a block multiplexer channel.

Operator console highlights

The consoles for System/370 are designed to increase operator efficiency. Model 155 offers a choice between a newly designed 15- or 85-character-per-second printer/keyboard console. An additional 15-cps printer/keyboard console can be installed, allowing the user to establish a separate console in an area of the installation other than adjacent to the CPU, such as the forms and scheduling area or the tape library. Each console would receive only those messages pertinent to its location.