2.5. File I/O Model

One of the distinguishing features of the I/O model on UNIX systems is the concept of universality of I/O. This means that the same system calls (open(), read(), write(), close(), and so on) are used to perform I/O on all types of files, including devices. (The kernel translates the application’s I/O requests into appropriate file-system or device-driver operations that perform I/O on the target file or device.) Thus, a program employing these system calls will work on any type of file.

The kernel essentially provides one file type: a sequential stream of bytes, which, in the case of disk files, disks, and tape devices, can be randomly accessed using the lseek() system call.