MemoRy ChiPS

• RAM Chip
(Random Access Memory) A type of memory that provides direct access to any byte on the chip. This “byte addressing” means that the contents of any byte can be read or written without regard to the bytes before or after it. In addition, read and write speeds are symmetrical. It takes no longer to write a byte than it does to read one. In contrast, writing to non-RAM memories such as flash takes considerably longer than reading (see flash memory).The most common RAM chip is the dynamic RAM (DRAM) used as a computer’s main memory. Any chip that has RAM in its name implies byte addressing and symmetric read and write speeds.



• ROM Chip
(Read Only Memory) A memory chip that permanently stores instructions and data. Also known as “mask ROM,” its content is created in the last masking stage of the chip manufacturing process, and it cannot be changed. Stand-alone ROM chips and ROM banks in microcontroller chips are used to hold control routines for a myriad of applications. ROMs were also widely used to hold the BIOS in early PCs as well as plug-in cartridges for video games.

Although EPROMs, EEPROMs, and particularly flash memory, are the kinds of non-volatile storage one hears about more often, ROM technology is mature, inexpensive and easy to integrate into any CMOS chip. The variations on the ROM chip are the following:

PROM (Programmable Read-Only Memory): A permanent memory chip in which the content is created (programmed) by the customer rather than by the chip manufacturer. It differs from a ROM chip, which is created at the time of manufacture. PROMs are used for storage when their content is not expected to change, but in many applications, they have given way to EPROMs and EEPROMs, which can be reprogrammed.


EPROM (Erasable Programmable Read-Only Memory): A rewritable memory chip that holds its content without power. EPROM chips are written on an external programming device before being placed on the circuit board. The chip requires an expensive ceramic chip package with a small quartz window that is covered with opaque, sticky tape. For reprogramming, the chip is extracted from the circuit board, the tape is removed, and it is placed under an intense ultraviolet (UV) light for approximately 20 minutes.

Although still used, EPROMS evolved into EEPROMs and flash memory, both of which can be erased in place on the circuit board.

EEPROM (Electrically Erasable Programmable Read-Only Memory): A rewritable memory chip that holds its content without power. EEPROMs are bit or byte addressable at the write level, which means either the bit or byte must be erased before it can be re-written. In flash memory, which evolved from EEPROMs and is almost identical in architecture, an entire block of bytes must be erased before writing. In addition, EEPROMs are typically used on circuit boards to store small amounts of instructions and data, whereas flash memory modules hold gigabytes of data for digital camera storage and hard disk replacements.

• Primary Storage

The computer’s internal memory, which is typically made up of dynamic RAM chips. Until non-volatile RAM, such as magnetic RAM (MRAM), becomes commonplace, the computer’s primary storage is temporary. When the power is turned off, the data in primary storage are lost. Data or instructions are stored in primary storage locations called addresses


The computer’s internal memory, which is typically made up of dynamic RAM chips. Until non-volatile RAM, such as magnetic RAM (MRAM), becomes commonplace, the computer’s primary storage is temporary. When the power is turned off, the data in primary storage are lost. Data or instructions are stored in primary storage locations called addresses