IBM System/370 Model 138

IBM System/370 Model 138

IBM System/370 Model 138
Announced Jun 30, 1976 and
withdrawn Nov 1, 1983
The following are edited excerpts from an IBM Data Processing Division technical press release distributed on June 30, 1976.

The new IBM System/370 Model 138 combines a faster internal speed with a variety of features that can help the medium-scale user expand computer applications more easily and economically.

The processor offers large main and reloadable control storage, performance increases under IBM virtual storage programming, and a number of standard features -- all at improved price/performance compared to the current System/370 Models 135 and 145.


The new model also offers increased system throughput -- the amount of time it takes to perform a given amount of work -- compared to the Models 135 and 145.

For example, the batch processing throughput of a Model 138 running a representative set of selected DOS/VS jobs was measured at 1.18 to 1.38 times faster than a similarly configured Model 135.

Additionally, the Model 138's internal speeds, or instruction execution rates, measured 29 to 36 percent faster than a Model 135.

Because of differences in configurations and applications at customer sites, individual users may realize different performance results.


The new machine uses the same high-density monolithic Metal Oxide Semiconductor Field-Effect Transistor (MOSFET) technology for main memory as other virtual storage System/370s. Each memory chip holds 2,048 bits of data. The Models 135 uses bipolar technology.

The Model 138 is available with 524,288 or 1,048,576 characters of memory, double the maximum capacity of the Model 135.

The large memory capacity and improved performance of the new processor can ease application development for users wishing to expand their communications interactive and data base operations.

The machine incorporates a reloadable control storage of 131,072 characters, five times the standard capacity of the Model 135 and four times the standard capacity of the Model 145. This portion of the processor stores programs that control the sequence of operations, as well as emulation and diagnostic routines.

The large control storage also accommodates standard and optional features available with the Models 138 and 148, allowing users to expand easily their system configurations.

Programming support

Extended control program support, implemented in the control storage, is a standard feature.

This extended support reduces the processor time needed to execute certain frequently-used supervisor functions in two IBM system control programs -- Operating System/Virtual Storage 1 (OS/VS 1) and Virtual Machine Facility/370 (VM/370).

Users of VM/370 on the Model 138 can realize a reduction of up to 55 percent in the processor cycles required in supervisor operations. This can expand a user's ability to move into the productive environment of interactive computing, such as the development of new application programs with a terminal online to the central computer.

For OS/VS 1 users, the savings in supervisor cycles in the Model 138 measured from 13 to 18 percent.

The Model 138 is supported by OS/VS1, VM/370 and Disk Operating System/Virtual Storage (DOS/VS).

Console, printers

The new system includes a display console of 1,920 characters, providing a fast and efficient means of communicating information on the status of the system to the operator. The new machine also provide an adapter for attachment of an optional IBM 3286 Model 2 printer for hard copy output of the display information.

IBM also announced a new model of its 3203 system printer, a compact unit with a rated speed of 1,200 lines per minute, for use with the new computer. One or two 3203 Model 4s can be attached to the new processor via an integrated printer adapter. In addition, a user may attach the larger IBM 1403 printer via an integrated printer adapter on the Model 138.


The Model 138 includes as standard a number of features that are options on the Models 135 and 145.

These include: APL assist, clock comparator and CPU timer, floating point, extended precision floating point, conditional swapping, and two block multiplexer channels.

Machine upgrades

Most installed Models 135 and 145 can be upgraded to the new computer's internal performance levels at customer locations. The upgrades include extended control program support for OS/VS1 and VM/370.

Machines that can be upgraded are Model 135s ranging from 262,144 to 524,288 characters of main memory, and Model 145-2s ranging from 262,144 to 2,097,152 characters of main memory.

Field upgrades to the improved version, designated the Models 135-3 and 145-3, will be scheduled to begin in the first and second quarters of 1977, respectively.

Prices, delivery

The IBM System/370 Model 138 is available under a new Agreement for Lease or Rental of IBM Machines, which provides for either a 48-month contract period or a standard monthly rental. Monthly rentals will be approximately ten percent higher than monthly charges under the long-term lease.

Under a 48-month contract, the Model 138 can be leased for $8,730 a month with one-half million characters of main memory, and for $11,415 a month with one million characters. Monthly rental prices are $9,600 and $12,550. Purchase prices are $350,000 and $435,000.

First customer shipments of the Model 138 will be scheduled to begin as follows: Model 138 with one million characters of main memory, fourth quarter of 1976; and Model 138 with one-half million characters of memory, first quarter of 1977.

The Model 138 will be manufactured at IBM's System Products Division facility in Endicott, New York, where it was developed.