18 milestones of mobile computing

The success of portable computing this decade is due at least partly to the pioneering work of many companies in decades past.

The iPad 2 to tremendous fanfare

Apple recently launched the iPad 2 to tremendous fanfare, and the device is being hailed as the latest and greatest portable computing device. Although more powerful convertible tablet PCs were available years ago, the iPad has flourished thanks to its intuitive touch-based interface and a wealth of easy-to-install third-party applications. Apple sold around 15 million iPads in 2010, and the company looks poised to have a big year with the iPad 2.

Important milestones in portable computing include devices just as single-chip calculators, 'laptops' that weighed more than 10kg, digital organisers and even a few older Apple inventions. Here's a look at 18 of the most notable mobile computers.

Legacy: It might seem strange to kick off a list of portable computing milestones with a calculator, nevertheless this little machine from Busicom was one of the first handheld devices that could carry out a computing function. So-called handheld calculators existed earlier this product, yet the Handy-LE was in fact the first calculator you could easily hold in your hand or fit in your pocket. The Handy-LE's small size was due to the single-chip calculator circuit - the Mostek MK610 - that carried out the device's computing functions.