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Notes on IBM 360

IBM 360 model 30Introduced in 1964

A computer for all: Contrasting with at-the-time normal industry practice, IBM created an entire new series of computers, from small to large, low to high performance, all using the same instruction set (with two exceptions for specific markets). This feat allowed customers to use a cheaper model and then upgrade to larger systems as their needs increased without the time and expense of rewriting software. Before the introduction of System/360, business and scientific applications used different computers with different instruction sets and operating systems. Different-sized computers also had their own instruction sets. IBM was the first manufacturer to exploit microcode technology to implement a compatible range of computers of widely differing performance, although the largest, fastest, models had hard-wired logic instead.

This flexibility greatly lowered barriers to entry. With other vendors, customers had to choose between machines they could outgrow and machines that were potentially overpowered (and thus too expensive). This meant that many companies simply did not buy computers.