udev is the device manager for the Linux 2.6 kernel series. Its primary function is managing device nodes in /dev. It is the successor of devfs and hotplug, which means that it handles the /dev directory and all user space actions when adding/removing devices, including firmware load.
Carla Schroder shows us how to manage Linux Hardware with udev. From the article:
In the olden days Linux administrators had a static /dev directory. It was inflexible and obese, containing 99% irrelevant entries, and we liked it that way. We didn’t mind hassling with makedev and struggling with major and minor numbers to enter the devices we actually wanted, or manually deleting the 1,000 useless /dev entries, because Real System Administrators love doing things the hard way. It makes us feel close to our hardware. The best part of the job is spending years acquiring and hoarding arcane bits of knowledge, which are then passed on to eager, fresh-faced noobs with the magical incantation, “RTFM, luser.”