IBM System/370

IBM System/370. It was a family of mainframe computers announced by International Business Machines as the successor to the highly successful IBM System/360. Introduced in 1970, the line maintained backward compatibility with its predecessor while introducing significant architectural enhancements, most notably the move to full virtual memory support. The System/370 series solidified IBM's dominance in the corporate data processing market throughout the 1970s and 1980s, serving as the backbone for major enterprises, governments, and academic institutions.

Overview

The announcement of the System/370 by International Business Machines marked a major evolution, not a revolution, in mainframe design. The primary goal was to protect the enormous investment customers had made in software and peripheral equipment for the IBM System/360. Key initial models included the IBM System/370 Model 155 and the IBM System/370 Model 165, which offered substantial performance improvements. This strategy ensured continuity for installations running critical applications for organizations like the Social Security Administration and major banks. The architecture's longevity was extended through subsequent generations of hardware, often referred to as IBM 3081 and IBM 3090 processors.

Architecture

The fundamental instruction set architecture of the System/370 was compatible with the IBM System/360, but it introduced several pivotal enhancements. The most critical was support for Dynamic Address Translation, which enabled full virtual memory via the Dataspace and later the Address Space concepts, managed by operating systems like MVS. Other major additions included new instructions for decimal arithmetic and enhanced channel capabilities for improved input/output performance. The architecture also saw the introduction of IBM System/370 Extended Architecture, which expanded addressing to 31 bits. These features were crucial for running complex transaction processing systems such as CICS and large-scale database management system software like IMS.

Models and evolution

The first models were built with traditional monolithic integrated circuit technology, but the line rapidly evolved. A landmark was the 1979 introduction of the IBM 4300 series, which used more advanced Very Large Scale Integration and offered a lower price point. High-end performance was pushed by subsequent processors including the IBM 3081, which utilized Thermal Conduction Module packaging, and the IBM 3090 with its vector processing facility. The final major iteration was the Enterprise Systems Architecture, which culminated in the IBM ES/9000 family. This evolution was driven by competition from other manufacturers like Amdahl Corporation and Hitachi, who produced plug-compatible mainframes.

Operating systems

A diverse ecosystem of operating systems was developed to exploit the hardware capabilities of the architecture. The primary systems for large-scale commercial use were OS/VS1, OS/VS2, and its successor MVS, developed by IBM's laboratories in Poughkeepsie, New York. For academic and interactive environments, VM/CMS provided a popular virtual machine environment. Mid-range systems often used DOS/VSE, while special-purpose systems included Transaction Processing Facility for the American Airlines SABRE system. The Unix operating system also became available on later models through projects like IBM AIX/370.

Impact and legacy

The System/370 family is considered one of the most successful and influential computer architectures in history. It established the mainframe as the indispensable platform for running the mission-critical applications of global Fortune 500 companies, financial institutions like Citibank, and government agencies including the United States Department of Defense. Its emphasis on backward compatibility set an industry standard, protecting software investments for decades. The architectural principles, particularly in reliability, availability and serviceability and virtualization, directly influenced later IBM systems like the IBM Z series and concepts now prevalent in cloud computing.

Category:IBM mainframe computers Category:1970 introductions Category:Computer-related introductions in 1970