Toshiba has unveiled a prototype hard-disk drive that's smaller than any currently on the market. It could appear in devices such as mobile phones and digital-music players before the end of the year.

The drive is the same length and width as an SD (Secure Digital) memory card and is 1 millimetre thicker. A prototype on display at the Consumer Electronics Show (CES) has a data storage capacity of 2GB. Toshiba plans to produce a sample drive with 4GB capacity around the middle of 2004.

The device is a miniaturized version of the kind of drive found inside a personal computer and features a recording platter, the media part of the hard-disk drive on which data is stored, that measures 0.85 inches in diameter.

It has a total weight of less than 10 grams and external dimensions of 3.3?x?24?x?32 millimetres.

Most current desktop computers use drives with a 3.5-inch diameter platter while notebook computers usually use 2.5-inch drives. Even smaller drives are used in digital music players ? Apple's iPod and iPod mini use 1.8-inch and 1.0-inch drives respectively, but until now no company has unveiled a smaller device.

Getting 2GB of data onto a recording platter this small did not require any special data storage technology. The disk media has a recording density of the drive is 80G bits per square inch which is the same as that used in Toshiba's 40GB 2.5-inch hard-disk drives aimed at notebook computer use.

The company anticipates a 10GB version of the 0.85-inch drive by the end of 2005.