Memory Chips

A memory chip is a chip that holds programs and data either temporarily or permanently. The major categories of memory chips are RAMs and ROMs.

RAM Chips

RAM stands for random-access memory. Random- access memory holds the data or instructions that the CPU is presently processing. The type of primary storage is RAM. That is, a collection of RAM chips builds primary storage.
Whenever a CPU writes data or instructions to RAM, it wipes out the previous contents of RAM, and when a CPU read data or instructions from RAM, it keeps their contents.

ROM Chips

ROM stands for read-only memory. A ROM chip is a memory chip that stores instructions and data permanently. Its contents are placed into the ROM chip at the time of manufacture and cannot be modified by the user. A CPU can read and retrieve the instructions and data from the ROM chip, but it cannot change the contents in ROM.
ROM chips usually contain special instructions for computer operations such as ROM BIOS. The variations on the ROM chip are the following:

• PROM (Programmable Read-Only Memory): A permanent storage device that becomes a read-only memory after it is written once by the customer rather than by the chip manufacturer. For example, a software producer can write instructions onto the PROM using special equipment.

• EPROM (Erasable Programmable Read-Only Memory): EPROM is a reusable PROM-chip that can be erased by a special ultraviolet light. EPROM holds its content until erased and new instructions can be written on it.

• EEPROM (Electrically Erasable Programmable Read-Only Memory): EEPROM-chip can be erased, either within a computer or externally, by electric power. The process usually requires more voltage than the common +5 volts used in logic circuits.

Primary Storage (Memory)

Primary storage (internal storage, main memory or memory) is the computer's working storage space that holds data, instructions for processing, and processed data (information) waiting to be sent to secondary storage. Physically, primary storage is a collection of RAM chips.
The contents are held in primary storage only temporarily. Capacity varies with different computers. Data or instructions are stored in primary storage locations called addresses.