There is speculation that an Apple iSlate tablet computer is to be launched in late January. I am less sceptical of this having spent some time seeing an Apple iPod Touch in use by a family. The smallest reasonable size for the iSlate would be a six inch screen, twice the size of the Touch and and iPhone. This is the same size as the screen on the Amazon Kindle. However, unlike the Kindle, the iSlate is likely to have no physical keyboard and therefore be small enough for a large pocket or handbag.
Visiting a networked family recently, I was struck by how useful their iPod Touch was. The family has a WiFi network, a desktop computer in the study and laptop which tends to sit on the coffee table, next to the controls for the Nintendo Wii. But the gadget that gets used most is an Apple iPod Touch, which tends to be on the kitchen bench or dining table.
The iPod is connected to the home wireless network. The iPod starts instantly, compared to about 20 seconds for the laptop. Also it is much more socially acceptable to use in a group of people, as it looks like a mobile phone. It takes only a few seconds to turn the iPod on, go to the web browser and look something up. The screen is large enough for looking at the bus timetable. This makes prospects for the rumoured Apple iSlate tablet computer very good.
Something like an iPod touch, but with a screen the size of a paperback book would seem to be a winner. Exactly how large a screen such a device should have is an interesting question. The iPod Touch (and iPhone) have a screen which is about size of a credit card, which is one of the standard sizes for international documents (ID-1 format: 85.60 × 53.98 mm).
The next standard size up would be that of a passport: 125 × 88 mm (ID-3 format or ISO B7). This would be about twice the size of the iPod Touch screen and the smallest reasonable size for the Apple iSlate. It would allow for a 6 inch screen, which is the size of the screen on the International Version of Amazon Kindle e-Book reader. A device this size would still fit in many larger pockets and in handbags. This is no coincidence, as passports are the size they are so that they will fit in a pocket or handbag, which is in turn sized to fit a human hand. Making the device this size would also allow it to be held comfortably in one hand. While modern electronics have allowed the size of many devices to shrink, these are still limited by natural units of measure, such as the size of a hand.
Such a small screen will not be suitable for everything. The iSlate will presumably have a USB interface. If plugged into a keyboard and mouse, the iSlate would be usable for entering more text. If interfaced to a large screen, such as a flat screen TV or LCD computer monitor and this would provide enough computing power for a web terminal. Apple may be reluctant to support this as it would undercut sales of their laptop and desktop computers. The iPhone and iPod Touch have a USB interface, but a keyboard is not supported (they also have a low resolution video out).