11. ROM, Read-only Memory

• ROM characterestics are:

  • Cannot be written into this type of memory.

  • Non-volatile memory

  • Most are factory programmed (i.e., written.)

• Programmable ROMs (PROMs)

  • Can be written once by user

  • A fuse is associated with each bit cell

  • Special equipment is needed to write (to blow the fuse)

• PROMS are useful:

  • During prototype development.

  • If the required quantity is small.