Photos: Looking back to the birth of the IBM mainframe

The first mainframe computers filled rooms, requiring operators to walk around to inspect all the various components, as can be seen in this shot of the S/360 model 85.

With the System/360 range, IBM set out to provide a mainframe for every need - from low-end machines to a model twice as powerful as IBM's meatiest computer at the time.

IBM invested some $5bn in developing the System/360, almost double its then annual revenue. However, the gamble paid off: the System/360 was a huge success for IBM and the architectural influence of the system can be seen in most mainframes today.

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Mainframes made possible the large-scale computer systems that are now commonplace.

The world's first automated passenger reservation system, Sabre, provided the basis for the modern web-based travel industry. Launched on two IBM 7090 mainframes, the system, whose first code was written in the 1960s, is today able to process billions of transactions a week.

The UK Met Office has also been using mainframes for 40 years, and still employs them to help produce four million forecasts each day.

Here you can see work taking place on an S/360 model 50.

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The first IBM mainframes relied on processors with clock speeds as low as 1MHz, and with memories of between 8KB and 8MB. In comparison to these early machines, modern IBM zEnterprise System mainframes can carry out hundreds of thousands of times more instructions per second.

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Much of the S/360's design stemmed from a 1956 IBM project to deliver a computer 100 times faster than the status quo.

IBM built the computer, known as the 7030, for the Los Alamos National Laboratory using a brand-new invention, the transistor.

Even though it missed its performance goals, the machine was a proving ground for numerous architectural features that still lie at the core of processor design. It could fetch and decode multiple instructions simultaneously, predict the results of calculations, speculatively execute code depending on its best guess and look ahead to unexecuted instructions to make best use of its internal resources.

Here you can see someone at work on the S/360 model 40.

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The S/360 model 25.

Soon after the System/360's launch, it faced competition from mainframes made by ICL, starting with the 1900 series.

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The S/360 model 65.

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A shot of the S/360 model 75.

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A fisheye view of an S/360 mainframe.

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One of a later family of IBM mainframes, the S/390.

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The mainframe isn't a relic with its best days behind it. It's still a workhorse for modern business.

While x86 servers fill datacentres today, mainframes are still used for transactional and back-office tasks by governments and large corporations.

Mainframes can typically support tasks that are very I/O intensive, making them suited to processing thousands of transactions per second or supporting tens of thousands of users and applications concurrently.

IBM estimates there are 1.1 million mainframe transactions every second. The machines process the vast majority of credit card transactions - equivalent to $6 trillion annually or the GDP of Japan.

Organisations can also be loath to move mission-critical applications from mainframes, favouring the stability of running a system on the same platform for many years.

This machine is part of IBM's modern family of mainframes, the zEnterprise System.

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With a few restrictions, programs that ran on the earliest IBM System/360 mainframes still work on the latest IBM mainframes.

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A diagram of a chip used inside one of IBM's zEnterprise System mainframes.

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