"ENDLESS LOVE" by Diana Ross and Lionel Richie was at the top of the charts. Ronald Reagan was staring down the Soviet Union. And Princess Diana, aged 20, was on her honeymoon with Prince Charles. It was August 12th, 1981 -- and International Business Machines of Armonk, New York, unveiled the IBM 5150, its new entry in the nascent market for "personal computers".

This beige box, with a starting price of $1,565, had a mere 16 kilobytes of memory and used audio cassettes to load and save data. (A floppy-disk drive was optional.) IBM's press release trumpeted the screen's "green phosphor characters for reading comfort" and "easily-understood operation manuals" that made it "possible to begin using the computer within hours."

IBM's previous attempts to launch a PC had failed. But today, 25 years on, the IBM 5150 is recognised as the ancestor of the modern PC, a crucial step in computers' evolution from geek playthings to indispensable tools of modern business and, for many people, private life. Roughly one billion PCs are now in use across the world; many office workers spend more time with their PCs than they do asleep or with their families. But the PC's spread has been uneven: in America there are 70 PCs for every 100 people, compared with 35 in France, 7 in Brazil, and 3 in China.

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