Character special files or character devices.
Character special files or character devices provide unbuffered, direct access to the hardware device. They do not necessarily allow programs to read or write single characters at a time; that is up to the device in question. The character device for a hard disk, for example, will normally require that all reads and writes be aligned to block boundaries and most certainly will not allow reading a single byte.
Character devices are sometimes known as raw devices to avoid the confusion surrounding the fact that a character device for a piece of block-based hardware will typically require programs to read and write aligned blocks.
