Spooling

• Used for sharing of non-sharable devices !!
• Blocking user when opening a file to an allocated non-sharable device causes delays and bottlenecks
• Use a spool to the an intermediate medium - such as a disk file
• Example includes a printer (lpr) spooler
• Only the printer can open certain files on the system, such as /dev/lpr
• Privledged access to files (associated with particular devices)

Here's a series of events that occur when a user (scm6mrw) tries to print a file :

1. The user (scm6mrw) opens /dev/lpr
2. Fileman opens /tmp/scm6mrw
3. scm6mrw writes to lpr file, Fileman diverts output to disc file
4. scm6mrw closes dev/lpr
5. Fileman closes /tmp/scm6mrw
6. Fileman sends filename "scm6mrw" to spooler
7. Spooler eventually opens /tmp/scm6mrw for reading
8. Spooler copies file to lpr
9. Spooler closes and deletes /tmp/scm6mrw