BACK at the dawn of the personal-computer era, in the late 1970s, millions of future programmers around the world got their first taste of writing software by using an ingenious little computer that cost less than $100 (about $240 in today's money).

For the vast majority of individuals who could not afford the $2,500 (more than $6,000 today) that IBM and others were about to start charging for their revolutionary PCs, the diminutive Sinclair ZX80 and its ZX81 successor were inspirations. If you didn't mind soldering the motherboard together yourself, the laptop-sized computer could be had in kit form for around $70. Your correspondent built two, one of each model. For a while Clive Sinclair, the innovative genius behind the ZX80/81 and much else, was the patron saint of schoolboys of all ages everywhere.

Sir Clive's current equivalent is Nicholas Negroponte, co-founder of the Media Laboratory at the Massachusetts Institute of Technology and the father of one of the worthiest causes in contemporary computing. In the sweep of its ambition, Mr Negroponte's pet project, One Laptop Per Child (OLPC), is remarkably similar to the thinking behind the original ZX80—giving inquisitive but economically deprived children the chance to feel the exhilaration of computer-based learning.

This week sees the realisation of Mr Negroponte's five-year dream. After field testing in Nigeria and Brazil, the OLPC project's first model, a rugged little green laptop called the XO that can run on batteries, solar power, a miniature windmill or hand- or foot-crank, goes into mass production. Schoolchildren in developing countries will start receiving the remarkable computer from October onwards.

The first batch is being supplied to some 30 of the world's poorest countries for $176 apiece. As production builds up at Quanta, the huge Taiwanese laptop-maker that is producing the machine for OLPC, Mr Negroponte hopes to drive the unit cost down to $100.

After more than a quarter century of progress, Moore's Law (chipmakers double the power of their semiconductors every 18 months or so) would suggest that the modern equivalent of the Sinclair machine should be about 20 times smarter. In reality, the XO is more like 1,000 times better. That's because innovations in information technology are not just cumulative; in closely coupled fields, they can have powerful multiplier effects. Also, some very smart people have refused to accept the conventional wisdom about how personal computers should be designed.

Overall, the XO tips the scale at around half the weight of a comparable laptop, gets over twice the usual running time when operating on battery power and costs less than half the normal price of an entry-level computer. One of the tricks has been to make many of the XO's components serve at least two purposes.

EPA

Wonder toy

To save power, for instance, the XO's liquid-crystal display (the biggest consumer of juice in a laptop) can be flipped from backlit colour to self-reflecting monochrome. That not only saves electricity, but helps the screen to be seen better in bright sunlight, where many XOs are likely to be used.

The number crunching is done by an AMD Geode processor running at a modest 433 megahertz, compared with the 2-3 gigahertz of conventional laptops. This processor allows the XO to use less energy and therefore generate much less heat. Result: no power-consuming cooling fan.

Indeed, all rotating parts have been dispensed with—to make the XO rugged enough for the wild. Instead of a hard drive, for instance, the XO uses a one-gigabyte “flash” chip to store data even when the power is off. The keyboard has a waterproof rubber coating and the case is sealed to prevent dust from encroaching. A pair of wireless antennas swivel up from the screen's sides like rabbit ears, endowing the laptop with two to three times the normal Wi-Fi range. When folded down, the antennas not only lock the case and but also seal off its various ports.

Better still, the Wi-Fi circuitry makes every laptop not just a communications device, but also a router. In other words, each laptop is part of a wireless mesh that relays the broadband signal from laptop to laptop—so those out of direct range can still get a connection to the internet.

If the ingenuity of the XO's hardware is impressive, the machine's software is truly ground-breaking. Red Hat, the world's largest Linux distributor, has provided an extremely compact version of its Fedora operating system, called Sugar, that uses a mere 130 megabytes of the XO's flash memory. By comparison, Windows XP requires 1.65 gigabytes.

The XO comes with a word processor, PDF viewer, Firefox web browser, media player, drawing tools plus the usual set of utilities. But it is the way the Sugar operating system lets the user work that's so clever. Instead of the usual hierarchical view of a computer's applications and data, Sugar organises everything around what has been used recently. Alternatively, it can group applications and files in terms of who is connected on the wireless mesh. As such, the mesh approach gives XO an array of collaborative tools that puts expensive business laptops to shame.

Clearly, trying to produce such an extraordinary product as a laptop that is kid-proof and capable of working in jungles, deserts or the bush, miles from the nearest grid connection, and all for the cheapest possible price, has concentrated minds remarkably. The XO offers a lesson for laptop-makers everywhere. In fact, quite a few have gone from ridiculing the OLPC project to trying to emulate or join it.

Most notable has been Intel. After first dismissing Mr Negroponte's laptop as a toy, the chipmaking giant suddenly rushed out a spoiler design of its own for developing countries, fearing it was about to be left out of an emerging market. Called Classmate, Intel's $225 laptop has failed to impress. Last week Intel admitted defeat tacitly by asking to join the OLPC association.

The question now is when can the rest of us get laptops as cheap and clever as the OLPC's radical design? Judging from the stir the XO has created, the answer is more likely to be months rather than years.