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(June 2010)| |Computer memory types| |Early stage NVRAM| Read-
only memory (ROM) is a class of storage medium used in computers
and other electronic devices. Data stored in ROM cannot be
modified, or can be modified only slowly or with difficulty, so
it is mainly used to distribute firmware (software that is very
closely tied to specific hardware, and unlikely to need frequent
updates). In its strictest sense, ROM refers only to mask ROM
(the oldest type of solid state ROM), which is fabricated with
the desired data permanently stored in it, and thus can never be
modified. Despite the simplicity, speed and economies of scale
of mask ROM, field-programmability often make reprogrammable
memories more flexible and inexpensive. As of 2007[update],
actual ROM circuitry is therefore mainly used for applications
such as microcode, and similar structures, on various kinds of
processors. Other types of non-volatile memory such as erasable
programmable read onl