MEMORY TYPES AND SIZES Types Random Access Memory (RAM) is memory that allows data to written to and read from any addres...
MEMORY TYPES AND SIZES Types
Random Access Memory (RAM)
is memory that allows data to written to and read from any address (location). 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.
Read Only Memory (ROM)
is a type of memory used were it is necessary to protect data or programs from accidental erasure. The original data stored in ROM can be read, but not changed. In addition, ROM memory is non volatile. This means that information will not be lost as the result of a loss of electrical power. ROM is normally used to store the programs that define the capabilities of the PLC.
Erasable Programmable Read Only Memory (EPROM)
provides a 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.
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