Raw device
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In computing, specifically UNIX, a raw device is accessed via a device file. For example, in many systems accessing /dev/hda1 will allow you to read/write directly onto/from the primary master hard drive. This raw device is typically used for paging and dumping. Applications like a Database management system can use raw devices directly enabling them to manage how data is stored rather than deferring this task to a File system.
On HPUX/SUN the raw-disk is recognized with /dev/rdsk/, on Linux with /dev/raw/raw*.
An ISO image file is the exact contents of a raw CD drive. Thus, they can be read or written by simply copying byte-for-byte between the raw device and an external file.
With respect to file storage, raw devices (partitions) are disk partitions without a file system on them. They are managed from outside the operating system.