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.

ROM BIOS(Read Only Memory Basic Input Output System): A set of routines stored in a ROM chip in a PC. The BIOS contains the drivers, or access methods, which activate the peripheral devices directly.

Memory Does Not Remember?: Primary storage holds its contents only temporarily - only as long as a microcomputer is turned on. When the machine is turned off, all the stored contents immediately vanish. It is therefore a good practice repeatedly to save your work in progress to a secondary storage device.

Capacity: RAM storage is usually represented in megabytes. For example, the IBM or IBM compatible PC that has 16 Megabyte of memory can hold 16 million characters. If a user uses a computer with small primary storage, he or she cannot run programs that require large memory such as later versions of WordPerfect for Windows, Photoshop or graphics software. Thus, the user had better check the amount of RAM when he or she buy a computer. A user also need to check the required RAM before he or she buys a software package.

Addresses: To locate the characters of data or instructions in memory, the computer stores them at locations known as addresses. Each address has a unique number. Addresses may be compared to post office mailboxes. Their numbers stay the same, but the contents continually change.

SIMM: Single In-line Memory Module (SIMM) is a narrow printed circuit board that holds many (8, 9, 12, etc.) memory chips. The card has either 30 pins or 72 pins.