Memory Module & Read-Only Memory (ROM)

Memory Module

RAM is mounted on a small circuit board called memory module. The memory module is mounted on motherboard. Three types of memory modules are as follows:

SIMM – SIMM stands for single inline memory module. In this module, the pins on opposite sides of the circuit board connect together to form a single set of contacts.

DIMM – DIMM stands for double inline memory module. In this module, the pins on opposite sides of the circuit board do not connect and form two set of contacts.

RIMM – RIMM stands for Rambus inline memory module. It houses SDRAM chips.

Read-Only Memory (ROM)

ROM stands for read only memory. The instructions in ROM prepare the computer for use. These instructions can only be read but cannot be changed or deleted. It is not possible to write new information or instructions into the ROM.

ROM stores data and instructions permanently. When the power is switched off, the instructions stored in ROM are not lost. Therefore ROM is called non-volatile memory.

The information in ROM is stored by the manufacturer. When the computer is switched on, the instructions in the ROM are automatically loaded into the memory of the computer.

Different types of ROM are as follows:

1. PROM

PROM stands for Programmable Read Only Memory. This form of ROM is initially blank. The user or manufacturer can wrile data on it using special devices. The user can write data and instructions on it only once. If there is any error in writing the instructions, the error cannot be removed from PROM. The chip becomes unusable. It is used to store the programs or data developed by user.

2. EPROM

EPROM stands for Erasable Programmable Read Only Memory. User can erase instructions or data stored in EPROM chip by exposing the chip to ultraviolet light and write new program.

3. EEPROM

EEPROM stands for Electronically Erasable Programmable Read Only Memory. In this memory, user can erase and write instructions with the help of electrical pulses. If there is any error in writing the instructions, the user can erase the contents electrically.

Difference between RAM & ROM

The difference between RAM and ROM is as follows:

RAM	ROM
RAM is a temporary memory.	ROM is a permanent memory.
RAM enables data to be both read and written to memory and data can be changed or deleted.	The instructions written in ROM can only be read but cannot be changed or deleted.
Instructions in RAM are continuously changing as different programs are executed and new data are processed.	It is not possible to write new information or new instructions into the ROM, so ROM is a non-volatile memory.
When the power is turned off, all the programs and data are erased from RAM. So RAM is a volatile memory.	When the power is turned off, the. instructions stored in ROM are not lost, therefore ROM is non-volatile memory.
The instructions are written into the RAM at the time of execution.	The instructions are written into ROM at manufacturing time.

Difference between PROM and EPROM

The difference between PROM and EPROM is as follows:

PROM	EPROM
PROM is a programmable memory.	EPROM is electronically programmable memory.
The user can write instructions on PROM only once.	The user can write instructions on EPROM many times.
The instructions written by the user cannot be erased from PROM.	The instructions written by the user can be erased from EPROM.
If there is an error while writing on PROM, it becomes unusable.	If there is an error while writing on EPROM, it can still be used again.
It provides less usability as instructions are written only once.	It provides more usability as instructions are written many times.