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System 360

From Computers to Computer Systems

IBM ® System/360 changed the IT industry forever, and it transformed how much of the world’s work gets done even today.

The most significant contribution of the IBM System/360 to the world of computing was its commitment to compatibility. It was the first product family that allowed business data-processing operations to grow from the smallest machine to the largest without the enormous expense of rewriting vital programs.

The vision was both sweeping and precise. Code written for the smallest member of the family had to be upwardly compatible with each of the family’s larger processors. Peripherals such as printers, communications devices, storage and input-output devices had to be compatible across the family.

The machine’s standardized input and output interfaces made it possible for customers to tailor systems to their specific needs. Introduction of the 8-bit byte, over the prevalent 6-bit standard, made it easier to handle both business information processing and scientific data processing. The era of separate machines for business and science was over. System/360 could handle logic instructions as well as three types of arithmetic instructions: fixed-point binary, fixed-point decimal and floating-point hexadecimal.

The six models announced in April of 1964 had a performance range of roughly 25-to-1, with the largest model being about 25 times more powerful than the smallest. The smallest model could perform 33,000 additions per second; the largest more than 750,000 additions per second. Six years later, after the introduction of additional models, the range jumped to 200-to-1.

No one at the time, including IBM, had ever written operating software for a compatible family of processors. IBM relied heavily upon its core logic modules, the breakthrough Solid Logic Technology (SLT). Utilizing a process called micro miniaturization, SLT was ten times as dense as the prevailing technology and 100 times as reliable.

If the basic measuring stick for software size is the number of lines of code produced, then System/360 was light years ahead of its time. The IBM 650 Magnetic Drum Calculator came with 10,000 lines of code, while the popular IBM 1401 came with 100,000 lines of code. In contrast, the System/360 had 1,000,000 lines of code initially, and eventually grew to 10,000,000 lines of code.

Despite the staggering evolutionary leaps computers have made in the last quarter-century, fundamental technical concepts introduced with the System/360 are still part of the backbone of the general-purpose computer industry. IBM’s release of the System/360 truly marked the beginning of the modern age of computing.