$ 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