major, minor numbers
major = driver (used by kernel when opening device to dispatch to correct driver)
minor = used by driver to differentiate device(s)

after disk the major, minor numbers are shown:
```
[jasras@n04.compute.vps2-lej1 ~]$ ls -l /dev/dm-*
brw-rw---- 1 root disk 253,  0 Oct 25 10:10 /dev/dm-0
brw-rw---- 1 root disk 253,  1 Oct 25 10:11 /dev/dm-1
brw-rw---- 1 root root 253, 11 Oct 28 19:58 /dev/dm-11
brw-rw---- 1 root root 253, 12 Oct 28 19:58 /dev/dm-12
```

available devices: `cat /proc/devices`

character devices vs block devices; what is the difference?

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[oreilly-device-drivers](https://www.oreilly.com/library/view/linux-device-drivers/0596000081/ch03s02.html)