Data: capture, storage, retrieval and recovery

To process data, we first capture it, then store it in a file or database, and later retrieve it.

• Data capturing: gathering data from different sources in digital form: keyboards, bar code readers at shops, remote sensors on satellites, and posts and comments on social media. Data from many different kinds of sources makes capturing complex.
• Data storage: keeping captured data for later processing. Data is produced very fast, so storage is a challenge, though cheaper storage devices help, and storage must be upgraded regularly. Large organisations use data servers: computers with large, fast storage. They are costly to set up and maintain, especially for small organisations and start-ups.
• Data retrieval: fetching stored data for processing. As databases grow, finding data quickly gets harder; keeping access time low is crucial.

Deletion and recovery. Data can be lost when devices crash, users delete by mistake, or hackers or malware delete it on purpose.

• Erasing data bit by bit takes a long time, so when data is 'deleted', the system usually only marks its space as free and shows it as empty; the bits stay.
• Data recovery is retrieving deleted, corrupted or lost data from secondary storage. It works only if the space has not yet been overwritten by other data.

Two security concerns:

• Unauthorised deletion: guard against it by limiting access, using passwords for accounts and files, and encrypting files against unwanted changes.
• Unwanted recovery: people throw away old or broken devices thinking deleted files are gone, but others can recover them, a threat to confidentiality. Use proper tools to delete or shred data before disposing of any old storage device.

Example (new): before giving an old laptop to a cousin, a student uses a secure-erase tool that overwrites the whole disk, instead of just emptying the recycle bin, so no one can recover her school files or saved passwords.