Installation guide
named pipe, or a UNIX domain socket). The driver handles all read and
write operations and follows the required protocols for the device.
_______________________ Note _______________________
Support for rz SCSI device names will be retired in a future
release. Any code that derives knowledge about a device from
the ASCII name or minor number may be impacted. All code
that uses the current device names will be compatible when the
change occurs because a mechanism that ensures binary
compatability will be provided. Existing interfaces such as
names and minor numbers will be fully supported.
There are three types of device files:
• Block device files
Block device files are used for devices whose driver handles I/O in large
blocks and where the kernel handles I/O buffering. Physical devices
such as disks are defined as block device files. An example of the block
device files in the /dev directory follows:
brw------- 1 root system 8, 1 Jan 19 11:20 /dev/rz0a
brw------- 1 root system 8, 1 Jan 19 10:09 /dev/rz0b
• Character device files
Character device files are used for devices whose drivers handle their
own I/O buffering. Disk, terminal, pseudoterminal, and tape drivers are
typically defined as character device files. An example of the character
device files in the /dev directory follows:
crw-rw-rw- 1 root system 7, 0 Jan 31 16:02 /dev/ptyp0
crw-rw-rw- 1 root system 7, 1 Jan 31 16:00 /dev/ptyp1
crw-rw-rw- 1 root system 9, 1026 Jan 11 14:20 /dev/rmt1h
• Socket device files
The printer daemon (lpd) and error logging daemon (syslogd) use the
socket device files. An example of the socket device files in the /dev
directory follows:
srw-rw-rw- 1 root system 0 Jan 22 03:40 log
srwxrwxrwx 1 root system 0 Jan 22 03:41 printer
Because disk and tape drivers often handle more than one device, each
device file has a major and a minor number. The major number specifies (to
the kernel) the driver that handles the device. The minor number is passed
to the appropriate driver and tells it the device on which to perform the
operation.
Administering the UNIX File System 7–13