Types Of Memory and its description

RAM
Random Access Memory (RAM) is memory where data can be
directly accessed at any address. Data can be written to and
read from RAM. RAM is used as a temporary storage area.
RAM is volatile, meaning that the data stored in RAM will be
lost if power is lost. A battery backup is required to avoid losing
data in the event of a power loss.

ROM
Read Only Memory (ROM) is a type of memory that data can
be read from but not written to. This type of memory is used
to protect data or programs from accidental erasure. ROM
memory is nonvolatile. This means a user program will not lose
data during a loss of electrical power. ROM is normally used to
store the programs that define the capabilities of the PLC.

EPROM
Erasable Programmable Read Only Memory (EPROM) provides
some level of security against unauthorized or unwanted
changes in a program. EPROMs are designed so that data
stored in them can be read, but not easily altered. Changing
EPROM data requires a special effort. UVEPROMs (ultraviolet
erasable programmable read only memory) can only be erased
with an ultraviolet light. EEPROM (electronically erasable
programmable read only memory), can only be erased
electronically.