Ratingen, Germany  - All-in-one PCs have actually been around for a long time. Office workers in the 1970s already had terminals on their desks containing all of the hardware within the monitor casing.

More recently Apple has led this sector based mainly on its iMac. Those distinctively flat computers are calling the tune for a variety of new all-in-one devices from the Windows world as well.

Apple offers the iMac with display sizes of 20 and 24 inches. The processors inside are modern dual-core chips from Intel - with 2.4 Gigahertz (GHz) of processing speed for the less expensive 999 dollar model and 3 GHz for the 1919 dollar top model. There are also differences between the two machines in the graphic chips, as well as the hard drive size and RAM - although the latter is easy to upgrade.

One way to save money is to buy memory and install it on your own.

That may well be the only internal component that can easily be upgraded on the all-in-one devices, though. The components are often so carefully tailored to fit together that replacing the individual parts is both difficult and expensive.

"Users who prefer to upgrade their machines on a regular basis shouldn't buy an all-in-one device," says Christof Windeck from Hanover-based c't magazine.

Sony's 999 dollar JS1 Is also designed as a compete solution. "To that extent it doesn't necessarily make sense to swap out individual components," the manufacturer reports. The hard drive is a standard SATA model, with 2 GB of RAM divided between two slots. Those can be easily replaced with two 2 GB cards: The board supports up to 4 GB in all.

The computers in HP's TouchSmart series represent that company's somewhat over-the-top pitch to "design-oriented customers" who "are interested in new interpretations of personal computing." The TouchSmart offers at least one ground-breaking element: an all-in- one PC with a touch screen interface.

The newest model in the series is the IQ800, with a screen diagonal of 25.5 inches. It features a Blu-ray drive, WLAN and a TV reception card. The machine is built around a Core 2 Duo processor supported by a GeForce-9600M-GS graphics card from Nvidia. The computer costs 1899 dollars.

Asus is also offering an all-in-one computer. The Eee Top takes a different approach then iMac, Touchsmart and Co.: The goal here is less to replace a classic PC with a nice-looking, space saving alternative than to provide a convenient computer for quick access to the internet as well as music and photos.

The device is initially being released in Germany and Austria in the ET1602 and ET1603 models with a touch-sensitive 15.6 inch screen. The computer, based on the technology behind Asus' Eee PC mini laptop, can be operated through its display using a stylus or the user's finger.

Windows XP Home is the standard operating system. Other features included USB ports, Gigabit LAN, WLAN, an integrated camera, a 160 Gigabyte (GB) hard drive, 1 GB of RAM and a card reader. The processor is only an Intel Atom chip, though. While energy saving, it provides less power than the double core processors used in the other machines.

The machine does have one interesting quirk - for some applications Windows does not need to be booted in order to use the computer. The user can launch the "Express Gate" function, powered by a small Linux system that provides online surfing capability as well as Instant Messaging and photo editing. The Eee Tops will be available for between 500 and 600 dollars.

The all-in-one computers are particularly popular in the education field. That applies especially to the iMac and its strong penetration of the US primary and higher educational markets. That can be attributed in no small part to the fact that the devices are space-saving. You can also position the keyboard and display independent of one another - something you can't do with a laptop.

An all-in-one computer is therefore a reasonable alternative to buying a laptop to replace a traditional desktop computer. If the device is intended for a child's room, Christof Windeck advises against wireless keyboard and mice: "They disappear in a hurry," Windeck says. (dpa)