For those who simply want to send and receive e-mail, there is a simpler, single-purpose device called MailStation.

They are differentiated from single-purpose devices like e-readers by "multiple connectivity technologies and a broad range of applications," though devices like the Nook Color have begun to blur that line somewhat.

Some of them will have full desktop computer functions while others will be single-purposes appliances like calendars, date books, note takers and other single-purpose devices.

A range of devices exist from mobile phones to single-purpose devices such as E-book readers.

For those who subscribe to St. Paul's dictum-"the good which I want to do, I fail to do"-single-purpose devices may have much to offer.

The robot is no more than a single-purpose device with a strictly limited capacity for decision-making.

Sony's product does have a distinct advantage over the single-purpose devices on the market.

From the doctor's office to wilderness hikes, flashlights have evolved from bulky, single-purpose devices into multi-purpose wonders.

And "appliance" certainly seems to be what Microsoft is aiming for with these rules: robust, essentially single-purpose devices that just work with no fuss or unnecessary complexity.

Do you want a rack of single-purpose devices costing from $100 to $250 each or do you want one $400 to $500 device, the PC?