Bonn, Germany - Home PC hard drives tend to be huge. That does not help much when you need spontaneous access to documents or photos while out and about. One option is an external hard drive or memory stick, but that means more devices to be carried along.

The alternative, these days, is web hard drives - personal storage space on the internet that can be accessed from almost any computer. The services are easy to use, although the uploading of data often requires a heft chunk of time. Security should be taken into consideration as well.

Web-based storage space is provided as an extra through a variety of fee-based services, including webmail services like Gmx ProMail. Gmx also offers some space as part of its no-cost version. New DSL contracts also frequently provide online storage space, says Holger Bleich from the Hanover-based c't magazine.

Furthermore, there is also a range of providers specialising in web-storage services, such as Wuala, Dropbox, Humyo, Box.Internet, DropBoks, MyDrive, and Xdrive, owned by AOL.

"More and more providers are choosing a model that provides a certain amount of capacity at no cost - and then demanding a fee for anything more," says Peter Knaak, a computer expert at the German consumer testing organisation Stiftung Warentest.

Xdrive, for example, offers 5 Gigabytes (GB) for free; that number can be bumped up to 50 GB for a charge of 9.95 dollars a month. Humyo offers 10 GB for free, while its 100 GB option costs 12.99 dollars after the second month.

It also offers a 250 GB option for around 26 dollars. A few services, such as Microsoft's Skydrive, are only available in a free version (with 5 GB).

The exception is Wuala. A test in the 11/2008 edition of PC Praxis magazine revealed that service offers only 1 GB for free, with everything above that fee-based. Users can gain extra free space by allowing their service to run via the peer-to-peer principle instead of a central server. That requires freeing up a portion of their hard drive for Internetwork use.

One thing seems clear for all the offers: online storage space is hardly cheap, particularly when compared with the purchasing price of external hard drives. Holger Bleich does not expect prices to fall much, but he does think that users will get more space for the same money - the same pattern observed in the external hard drive market.

You can register for most of the services simply by using your web browser, Holger Bleich explains. In a few cases, you have to install special software, known as a client, onto the computer.

Data being stored to a network drive is technically speaking an upload, akin to placing a video on YouTube. By the same logic, accessing the data is a download.

Downloads are uncomplicated: Good broadband connections using DSL technology or the like brings speeds of up to 16 Megabits per second (Mbit/s). It's the upload process that shows some of the flaws in the online hard drive model: Speeds in that direction tend to max out at 1 Mbit/s, and even those figures are for ideal cases, Bleich explains.

"You'll need 13.2 minutes for a 100 MB album of MP3s. A 4.8 GB DVD requires a hefty 10.6 hours," or even longer.

Data security is also a reasonable concern with these services. "After all, online storage is very different from external hard drives, where someone has to break down your apartment door to get to the data," says Peter Knaak. You should therefore give some thought in advance whether any sensitive data should be stored in that way.

In theory data is vulnerable to interception when it's uploaded or downloaded. "The minimum bar for security for data headed to the server and back should therefore be SSL or TLS encryption," says Martin Bierwirth from the Federal Agency for Security in Information Technology (BSI). If a service provider doesn't offer either technology, then you are advised to look elsewhere.

At the very least, sensitive data like address books should be stored in encrypted form, Martin Bierwirth says.

"The simplest way for Windows users to do this is to create a Zip archive with the 'encrypt data' option activated," he says. Or you can use a specialised encryption program like TrueCrypt or PGP (Pretty Good Privacy), both available for free.

(Internet: http://www.wua.la; http://www.getdropbox.com; http://www.humyo.de; http://www.box.Internet; http://www.dropboks.com; http://www.mydrive.ch; http://www.xdrive.com; http://skydrive.live.com.)