Perhaps the most important invention in human history is about to take its greatest leap forward since Gutenberg's printing press in the 15th century - pen and paper are going digital.Despite predictions that we would all be reading books and consuming news and other media through computer screens and hand held electronic devices by now, our addiction to paper based technology has proven difficult to shake. This is no surprise given that paper has worked well for more than two millennia, with improvements to the printing and manufacturing processes making it an even more versatile and accessible medium for mass communication in the 21st century. It's not just cost and availability that sustains the printed page, there's a certain appeal to the tactile, hands-on nature of a book or even single sheet of paper that we are more comfortable with - for proof, take a look at the printed documents that could have been read on-screen but are instead piled next to your office photocopier. After all, curling up on the couch with a glass of red and a PDA doesn't quite have the same appeal.A true merger of on-screen and paper based technologies that will combine the best of digital and physical interfaces is on its way - flexible displays that look and act like paper without the limitations of content that can never be changed. Potentially this means you will be able to access any novel, magazine, newspaper and eventually even video, through one actual "book", then delete it when you're finished and download another through a wireless network. Several projects around the world are working towards this goal. Aviation electronics and communications company Rockwell Collins is involved in developing flexible display media and the US Defense Advanced Research Projects Agency (DARPA) is investigating possible military applications for lightweight, durable and power efficient digital paper.One of the leaders in private sector development of the concept is Gyricon Media, a spin-off of the Xerox Palo Alto Research Center (PARC) and the Massachusetts Institute of Technology Media Laboratory. Known as Smart Paper, the product was conceived by Gyricon's current research director Nicholas Sheridon in the early 70's. The technology is based on tiny "bichromal" plastic beads embedded in flexible transparent film that can be switched between contrasting colours such as black and white. Text or images are created by the application of electric current that rotates one hemisphere of each bead towards the viewer. This electronic text will remain visible until a different voltage pattern is introduced. The process of deleting and "re-printing" the contents of digital paper will require an input device to apply the required voltage pattern. Initially this device is likely to look like standard printer, but eventually the task will be performed by highly portable scanning "wands" that can re-configure a digital page simply by being passed over its surface. The Gyricon system, Greek for "rotating image", was field-tested during 2001 at the Macy's department store in the US where 15 signs were used in a retail setting. The "paper" is not yet flexible, but re-useable, full-colour e-magazine's may be only a few years away. Competitor E-Ink was developed independently in 1995 uses similar principles, transforming the appearance of high-tech "paper" using small amounts of electric current. In one possible manifestation of E-Ink, tiny polymer microcapsules about the diameter of a human hair containing many charged white and black particles (as opposed to the bichromal beads used by Gyricon) are suspended in a clear fluid with one of the colours being visible to the viewer depending on whether the charge applied is positive or negative. The liquid medium that carries the microcapsules will be printable using existing screen-printing techniques onto glass, fabric, paper and a range of other surfaces. E-Ink's development was boosted by corporate backing and an R&D grant from DARPA. The technology has also been tested in US department stores and is being further researched by Philips - which is investigating the use of E Ink technology in PDA displays - and others like Japan's Toppan Printing Company which has produced a prototype colour electronic-ink display. These technologies are expected to be widely available for commercial uses like retail signage by 2005. The major hurdle is the high cost involved in producing electronic devices on such a small scale. Just as a silicon chip that cost $100 to produce in the late 80's now costs a few cents, a solution that will drive the technology forward is inevitable. Fujitsu Laboratories, among others, has made progress in the efficient production of thin-film displays, but one of the most interesting breakthroughs is based on the same process that transformed publishing in 1863 - Roll-to-roll manufacturing. Rolltronics have pioneered the application of this process to micro-electronics and are working in conjunction with Gyricon and E-ink to drastically reduce costs of producing digital paper.Rolltronics sees benefits way beyond the electronic book in replacing silicon wafers with flexible plastic that can be produced in continuous sheets one meter wide and 10 kilometres long. Wallpaper could change colour or provide mood lighting via millions of microscopic lights, milk cartons could tell you when they are out of date, glass would become obsolete in the manufacture of computers and clothing could be integrated with powerful electronics. The storage capabilities of this new material would mean that 5TB (trillion bytes) of data could be stored in the same space as a standard 3.5 inch hard disk.The compelling reasons to encourage and look forward to this technology jus keep piling up. Its hard to see traditional paper ever disappearing altogether, but more trees will be left standing when we can all download the morning paper, and spin-off technologies will provide huge benefits in unexpected areas such as the cheap and efficient plastic solar cells.Ed Note: The Digital Paper concept discussed here is no the same as the Anoto system, which utilises standard paper as a computing interface via a near invisible printed grid that can be "seen" by a special digital pen.Read more at Gizmo on the Anoto Concept at Gizmo.com.au story 1286, or see article 1553 for details on Logitech's recently released digital pen.