From LQWiki

/dev is one of the root directories and represents the entry-point for all devices in the system.

Typically, every disk, terminal, usb-port etc. has an entry point in /dev.

• /dev/ram memory
• /dev/md# raid disks
• /dev/hda first IDE disk
• /dev/hda1 first partition on first IDE disk in older kernels
• /dev/hdb second IDE disk
• /dev/hdb1 first partition on second IDE disk
• /dev/sda first SCSI/SATA disk
• /dev/sda1 first partition on first scsi disk
• /dev/sdb second scsi disk
• /dev/sdb1 first partition on second scsi disk
• /dev/sdb1 first partition on second scsi disk
• /dev/mapper layout scheme for LVM partitions