Linux General Interview Question:

What is block device and character device?

Submitted by: Administrator

$ ls -altr /dev/
brw-rw---- 1 root disk 8, 6 2010-07-26 14:20
sda6 --> block device
crw-rw---- 1 root root 10, 59 2010-07-26 14:21 device-
mapper --> character device
Answer :

Character devices deal with IO on a character by character
basis. The most obvious example is a keyboard, where every
key generates a character on the device. The mouse is
another. Every motion or button click sends a character to
the /dev/input/mouse0 device. To test it out do
$cat /dev/input/mouse0 , then move your mouse (see what
happens)

Block devices read data in larger chunks or blocks. Data
storage devices, such as IDE hard drives (/dev/hd), SCSI
hard drives (/dev/sd), and CD-ROMs (/dev/cdrom or /dev/sr0)
are block devices. IO interactions with block devices
transact with chunks of data (blocks), which allows large
quantities of data to be moved back and forth more
efficiently(unlike character device). eg: $df -h

Generically, block devices can be mounted and are cached,
and char devices are for communication devices, aren't
cached nor block aligned, and can't be mounted.

Specifically, /dev/scd* (block) are for cdroms, providing
the block access and commands for ejecting, closing,
playing, etc.

The corresponding character device for the cdrom is /dev/sg1
Submitted by: Administrator