Raw device

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.

An ISO 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.