In the case of conventional hard disks, which are still in widespread use today, all of the information on your computer is stored on a set of magnetised discs. Known as "platters", these discs are arranged on top of one another in a stack that rotates up to 15,000 times a minute. If these hard-working components suffer a disk crash or are damaged by some other hardware fault, then the information written to them can be lost forever. While disks are rarely affected by technical defects, they do occur - which makes them all the more serious.

Data is saved to and accessed from hard disks electromagnetically, with the help of read/write heads. To prevent these heads touching and scratching the platters as they rotate during disk operation, the heads are supported by a wafer-thin layer of air. If the hard disk is subjected to any shocks while it is operating, these read/write heads can touch the surface of the platters and cause (irreparable) damage. In technical terms, this is referred to as a "head crash".

Modern storage systems, known as solid-state drives (SSDs), are significantly smaller and also much faster than HDDs (hard disk drives). This is why these kinds of newer drives are used in smartphones and USB memory sticks. When it comes to SSD drives, there are two basic working principles. Flash-based SSDs use electrical charge to store data on transistors, which is a very energy-efficient technique.

Whatever kind of storage you use, the lifetime of your device will be the limiting factor. Electrical charge on transistors can be maintained for only a few months to a few years. And while magnetic polarisation is longer-lasting, it does not last for ever. While the device itself may continue to be in good working order, the data it stores may nonetheless be lost if it is unused or stored incorrectly.

Smartphones and tablets - a special case?

In the case of mobile devices like smartphones and tablets, the risk of a technical fault is typically much less likely than simply losing the device or having it stolen. Loss or theft is the classic worst-case scenario here, and you should assume that your data and files are gone forever. The only reliable safeguard in this case is to create backups that you can simply restore if your device goes missing. We've put together some tips for backing up your phone data, as well as some general information about device security.

Physical safeguards

• Avoid subjecting your computer to any shock or vibration while it is running.
• Keep storage media in a cool and dry place, and do not leave them exposed to direct sunlight.
• Keep several copies of your storage media in different places.
• Always ensure you label your storage media.

How to avoid deleting things by accident

• Don't set up the recycle bin in your operating system and other apps (e.g. mail program "Deleted" folder) to be emptied automatically: first check if any important files have ended up there by mistake.
• Take care when reusing existing text files as a template for new documents: always save the file first using a different name if you want to keep the older version of the file.
• Install a modern antivirus program, make sure your firewall is activated and never open emails from any suspicious sources. More information on this topic is provided in the "How to get protected" section and the Bürger-CERT newsletters.
• Store operating system or application files on one hard disk and save the files that you yourself create onto a different disk. This makes backing up the second disk much easier.
• From time to time, check whether the data that you have saved can still be accessed by the software you are now using: the rapid pace of technological change can create problems with file formats.

How to recover lost data

If data that you have deleted by accident or which has become "corrupted" cannot be restored by your backup software, then data recovery software can literally come to the rescue in this scenario. While there are a lot of programs available from many software developers, you should always get in touch with specialists - who typically run a dedicated data recovery lab - if you have no experience in using such tools. Otherwise, there's a risk that you will simply make a bad situation worse. Expert data recovery can be pretty expensive, however, so you do need to weigh up the costs against the benefits.