These approaches can combine a smaller SSD that stores the operating system and applications and a larger HDD that is used for user data, or a hybrid HDD that has flash memory inside a HDD that is used to store frequently accessed data on the flash with less used data kept available on the HDD.

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Write caching would store data to be written on the HDD in flash memory initially until enough data was in the flash cache to do an efficient write to the HDD disks.

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And instead of a hard drive, it's designed to store data on flash cards.

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