Electronic paper comes in many sizes, but the one most manufacturers are hoping will break the mainstream is the A4 equivalent they expect to replace everything from newspapers to laptops.
The latest such prototype we've seen comes from KDDI R&D Laboratories in Japan and is the first designed to securely complement a mobile phone.
The pre-production 'Portable Viewer' is a 13.1-inch 4,096-colour e-paper display made by Bridgestone that connects to a phone by infrared to display exactly what's on the screen of the smaller device.
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KDDI says it's ideal for travelling salesmen who currently rely on bulky laptops for making presentations. The Portable Viewer could do the same job by downloading data through the phone from a corporate website.
As you may have guessed, that also hints at another potential selling point – data security.
Instead of keeping sensitive information in easily lost laptops, companies could store it all in the 'cloud' for access by phone only when needed. The display has no controls, leaving everything in the hands of the phone user.
The fact that data in the e-paper unit disappears from it when the screen is wiped is clearly likely to be a strong attraction to careless government agencies in the UK ... er, we mean worldwide.