Today$$s digital devices use a variety of storage technologies.

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storage technologies, such as hard disks, store data as particles oriented north or south. A hard disk drive provides multiple

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for data storage that are sealed inside the drive case to prevent airborne contaminants from interfering with the read$-$write heads. Hard disks are less durable than many other types of storage, so it is important to make a copy of the data they contain.

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storage technologies store data as a series of

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and lands on the surface of CDs and DVDs$.$ Storage technologies, such as CD$-$

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$,$ are used for distributing software and music, but you cannot alter the disc$$s contents.

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technology allows you to write data on a CD or DVD$,$ but you cannot delete or change that data. Rerecordable or

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technology allows you to write and erase data on a CD or DVD$.$

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state storage technologies, such as USB flash drives, store data by activating electrons in a microscopic grid of circuitry. A backup is a copy of one or more files that have been made in case the original files become damaged. A good backup plan allows you to restore a device$$s operating system, software, data files, settings, accounts, and profiles in case of a massive hardware failure or virus infection. Personal computer backups are typically recorded on

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hard drives, USB flash drives, network servers, and online storage services. An easy way to get a backup of important data files is to use the

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command to make duplicates and store them on a USB drive. Backup utilities such as File History and Time Machine use a technique called file

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to make sure that files on two devices are the same. A disk

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is a bit$-$for$-$bit copy of the data from all sectors of a hard disk.