Iconic consoles of the IBM System/360 mainframes

The IBM System/360 was a groundbreaking family of mainframe computers announced on April 7, 1964. Designing the System/360 was an extremely risky “bet-the-company” project for IBM, costing over $5 billion. Although the project ran into severe problems, especially with the software, it was a huge success, one of the top three business accomplishments of all time. System/360 set the direction of the computer industry for decades and popularized features such as the byte, 32-bit words, microcode, and standardized interfaces. The S/360 architecture was so successful that it is still supported by IBM’s latest z/Architecture mainframes, 55 years later.

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Although the S/360 models shared a common architecture, internally they were completely different to support the wide range of cost and performance levels. Low-end models used simple hardware and an 8-bit datapath while advanced models used features such as wide datapaths, fast semiconductor registers, out-of-order instruction execution, and caches. These differences were reflected in the distinctive front panels of these computers, covered with lights and switches.

This article describes the various S/360 models and how to identify them from the front panels. I’ll start with the Model 30, a popular low-end system, and then go through the remaining models in order. Conveniently IBM assigned model numbers rationally, with the size and performance increasing with the model number, from the stripped-down but popular Model 20 to the high-performance Model 195.

This is an incredibly detailed article on this – relatively speaking – arcane topic, filled with beautiful photography. A delight to read.