Hardware suppliers have been given the green light to ramp-up production of all of the components needed to build millions of the low-cost machines.
Previously, the organisation behind the scheme said that it required orders for 3m laptops to make production viable.The first machines should be ready to put into the hands of children in developing countries in October 2007.
"There's still some software to write, but this is a big step for us," Walter Bender, head of software development at One Laptop per Child (OLPC), told the BBC News website.
The organisation has not said which countries have bought the first machines.$100 Laptop's chief software engineer Chris Blizzard on how the innovative memory and screen save energy.
Getting the $100 laptop to this stage has been a turbulent journey for the organisation and its founder Nicholas Negroponte.
Since the idea was first put forward in 2002, the low-cost laptop has been both lauded and ridiculed.
Intel chairman Craig Barret famously described it as a "$100 gadget" whilst Microsoft founder Bill Gates questioned its design, particularly the lack of hard drive and its "tiny screen".
Other critics asked whether there was a need for a laptop in countries which, they said, had more pressing needs such as sanitation, water and health care.
Professor Negroponte's response has always been the same: "It's an education project, not a laptop project."Clickable guide: XO laptop
The view was shared by Kofi Annan, ex-secretary General of the UN. In 2005, he described the laptop as an "expression of global solidarity" that would "open up new fronts" for children's education.
And as time passed, even some of the critics have changed their stance. Earlier this month, Intel, which manufactures what was considered a rival machine, the Classmate PC, joined forces with OLPC.
The innovative design of the XO machine has also drawn praise from the technical community.
Using open source software, OLPC have developed a stripped-down operating system which fits comfortably on the machine's 1GB of memory.
"We made a set of trade-offs which may not be an office worker's needs but are more than adequate for what kids need for learning, exploring and having fun," said Professor Bender.
The XO is built to cope with the harsh and remote conditions found in areas where it may be used, such as the deserts of Libya or the mountains of Peru.
For example, it has a rugged, waterproof case and is as energy efficient as possible.
"The laptop needs an order of magnitude less power than a typical laptop," said Professor Bender. "That means you can power it by solar or human power."
Governments that sign up for the scheme can purchase solar, foot-pump or pull-string powered chargers for the laptop.
And because it may be used in villages without access to a classroom, it has also been designed to work outside. In particular, the green and white machines feature a sunlight-readable display.
"For a lot of these children it's their only book and we want them to have a first class reading experience," said Professor Bender.
The XO will be produced in Taiwan by Quanta, the world's largest laptop manufacturer.
The final design will bring together more than 800 parts from multiple suppliers such as chip-maker AMD, which supplies the low-power processor at the heart of the machine.
"This is the moment we have all been waiting for," Gustavo Arenas of AMD told the BBC News website.
"We certainly believe very strongly in the mission and vision of OLPC so finally starting to see it come to fruition is not only gratifying, it is also rewarding."
Test machines, on which the final design is based, are currently being put through their paces by OLPC.
"We keep laptops in the oven at 50 degrees and they keep on running," said Professor Bender.
Field testing is also being done in countries such as Nigeria and Brazil.
However, the names of the governments that have purchased the first lots of machines have not been released.The XO currently costs $176 (£90) although the eventual aim is to sell the machines to governments for $100 (£50).
Also see: Intel and $100 laptop join forces
One Laptop Per Child OLPC
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