UNIX for Dummies Questions & Answers

One of the unique things about Unix as an operating system is that regards everything as a file. Files can be divided into three categories; ordinary or plain files, directories, and special or device files.

Directories in Unix are properly known as directory files. They are a special type of file that holds a list of the other files they contain.

Ordinary or plain files in Unix are not all text files. They may also contain ASCII text, binary data, and program input or output. Executable binaries (programs) are also files, as are commands. When a user enters a command, the associated file is retrieved and executed. This is an important feature and contributes to the flexibility of Unix.

Special files are also known as device files. In Unix all physical devices are accessed via device files; they are what programs use to communicate with hardware. Files hold information on location, type, and access mode for a specific device. There are two types of device files; character and block, as well as two modes of access.

Block device files are used to access block device I/O. Block devices do buffered I/O, meaning that the the data is collected in a buffer until a full block can be transfered.

Character device files are associated with character or raw device access. They are used for unbuffered data transfers to and from a device. Rather than transferring data in blocks the data is transfered character by character. One transfer can consist of multiple characters.