By Chris Long BBC ClickOnline producer

The personal computer has come of age. This week the PC celebrated its 21st birthday and by this we mean the IBM PC.

There are people who argue over which computer can rightly be called the first PC.

Some would say it was the Simon computer back in 1950.

Others will tell you it was the build-it-yourself Altair introduced in January 1975. Some insist it was Commodore Pet in 1976, one of the first desktop computers with a built-in screen.

And it goes without saying that the vociferous Apple crowd will swear blind that the two Steves, Jobs and Wozniak, built the first truly successful PC, the Apple II, in 1977.

Foundations laid

But they are all wrong. The first PC was the IBM PC, launched on 12 August 1981.

IBM's 5150 took the market by storm

Until then we had micros, minis, home computers, personal minicomputers and many more names for the same box. But it was the IBM that locked the initials PC in stone.

With a modest 4.7Mhz 8088 Intel processor and 16 kilobytes of memory, the IBM PC took the market by storm.

It ran PC DOS 1.0 which IBM had licensed from a young man based in Seattle called Bill Gates.

The world of the late 70s and early 80s was a strange place. In 99% of companies the typewriter was used to produce letters and the rest of us used pen and paper.

IBM thought they would sell about 40,000 PCs in the first year. They got it wrong. They sold that number in the first couple of months.

Toying with Dos

By the mid-1980s IBM were losing market share to the other manufacturers who joined the PC party.

The Apple II: The first truly successful PC?

As a result it targeted the operating system as in need of an upgrade and, with its then best friend Microsoft, started work on OS/2, a new operating system.

It launched OS/2 with a matching PC called the PS/2. Dos is dead, said IBM and Microsoft alike, long live OS/2.

IBM promptly waited 18 months to deliver the full version of the software which quickly turned out to be a disastrous move.

Reports of Dos's demise were somewhat exaggerated. The PS/2 PC was not faring well and it was quietly dropped.

IBM continues to build PCs to this day, though the branding and the company that launched the original has changed almost beyond recognition.

With more than 600 million PCs in use, it is fair to say that this machine's older, slower sibling launched 21 years ago was one of the most important products of the 20th Century.

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