The IBM System/370

System/370 was designed to address the data processing needs that were becoming apparent in the 1970s, driven by large databases and the simultaneous operation of multiple programs. Banks, airlines and retailers all found the architecture especially useful for remote computing, in which management information networks in the field make use of a centralized computer. Along with being faster and more compact than other mainframes, System/370 was also easily expandable.

In developing System/370, IBM set out to meet three major objectives. The first was performance. It had to have faster processing, more storage capacity and greater flexibility than the popular System/360, which had debuted in 1964. It also had to be affordable for small and medium-size companies that wanted to purchase their first computer or expand their existing system. The third objective was perhaps the most important. IBM didn’t want System/360 customers to have to start over from scratch, so System/370 would have to be fully backward compatible.

IBM CEO Thomas J. Watson Jr. was adamant that System/370 not cause the type of disruption that resulted during the release of System/360, which replaced all existing IBM products. In a speech to IBM employees shortly before the debut of Models 155 and 165, Watson Jr. said, “Despite the unprecedented success of 360, we should not forget the tremendous problems we encountered in making such a sweeping change in our entire product line, and we should not forget the difficulties that we created for our customers. We don’t want to make the same mistakes twice.”

System/370 met all three objectives, enabling users to achieve much higher performance and storage capacity per data processing dollar, while protecting the investment that many customers had made in System/360. “With System/370, we have achieved greatly improved performance by putting much of the advanced technology of IBM's ultra-high-performance computers within the reach of medium- and large-scale computer users,” said Francis G. Rogers — better known as “Buck” Rogers — president of IBM’s Data Processing Division, upon the system’s release. “And System/360 users will be able to run most of their existing programs on the new system without change.”

When System/370 debuted, Watson Jr. predicted that the computer would “stand out as the landmark for the 1970s.” As it turned out, it was IBM’s leading mainframe through the ’80s.

Part of System/370’s success can be attributed to the fact that it was among the first computers to include full support for virtual memory, which was announced in August 1972. Virtual memory relieves real storage facilities of the burden of holding an entire application during use. Instead, real storage residence is governed by usage frequency. By fully utilizing virtual storage, System/370 enabled programmers to use more memory than might be physically available. And users gained significantly more flexibility in application design. They could write more comprehensive programs and simplify operational program maintenance. 

One of the first customers was the Boston-based State Street Bank and Trust Company, which ordered four models of the System/370 the day it was announced. The bank previously had nine computers running 2,000 different programs. By switching to System/370, it was able to run all its programs on a single mainframe. “The large data storage capacity of the new system is just what we need,” said Bradford S. Tripp, vice president of the bank’s computer services division.

Many manufacturers turned to System/370 to help manage large inventories. Willcox & Gibbs, a maker of industrial sewing equipment and parts, used the computer to produce a daily status report on more than 60,000 items in stock to keep inventories in close relationship with sales. System/370 “holds down inventories while our sales volume soars at a 30 to 40 percent rate annually,” said Jerome Gilbert, the company’s executive vice president.

Aeroquip Corporation, whose spacecraft fittings were a part of in-flight maneuvering rockets on the Gemini and Apollo missions, used System/370 to track orders for more than 71,000 parts daily and enable management to quickly obtain information about customer orders and production efficiency. “With System/370, we have actually reduced our hardware costs,” said Burleigh Cook, the company’s manager of data processing. System/370 was also used by NASA for structural analysis.

System/370 also helped transform central warehouse management. Once an inventory of product types and customer lists was entered into the system, the ongoing entry of production figures, deliveries and orders made it possible to maintain a continuous overview of inventories and delivery capability. Warehouse associates could read information on the mainframe’s screen or print it out, along with all stock requisitions, delivery notes and invoices.

But the real breakthrough with System/370 was silicon.

The silicon chips in System/370 marked a major departure from conventional computer design, both for IBM and the industry at large. It marked an inflection point in computer design, one that would outlive the system itself, which was finally replaced by IBM System/390 in 1990. Data would no longer be stored in magnetically charged iron ferrite cores. Silicon chips, with their very high circuit density, could store data more quickly and in about half the space required by iron ferrite cores. From this point forward, iron was out, silicon was in.