Information Technology Reference
In-Depth Information
Memory
Type
Abbreviation
Name
Description
Volatile
RAM
Random access
memory
Volatile storage devices that lose their contents if the current is
turned off or disrupted.
SRAM
Static Random
Access Memory
Byte-addressable storage used for high-speed registers and caches.
DRAM
Dynamic Random
Access Memory
Byte-addressable storage used for the main memory in a computer.
DDR SDRAM
Double Data Rate
Synchronous Dynamic
Random Access Memory
An improved form of DRAM.
Nonvolatile
ROM
Read-only memory
Nonvolatile storage devices that do not lose their contents if the
current is turned off or disrupted.
PROM
Programmable
read-only memory
Memory used to hold data and instructions that can never be changed.
PROMs are programmed in an external device like EPROMs.
EPROM
Erasable
programmable
read-only memory
Programmable ROM that can be erased and reused. Erasure is
caused by shining an intense ultraviolet light through a window that
is designed into the memory chip. EPROM chips are initially written
in an external programmer device and must be removed from the
circuit board and placed back in the device for reprogramming.
EEPROM
Electrically erasable
programmable
read-only memory
User-modifiable read-only memory that can be erased and
reprogrammed repeatedly through the application of higher than
normal electrical voltage.
Flash
Used for storage modules for USB drives and digital camera memory
cards. Able to erase a block of data in a flash.
NOR Flash
Flash memory that supports 1-byte random access so that
machine instructions can be fetched and executed directly from the
flash chip just like computers fetch instructions from main memory.
NAND Flash
Flash Translation Layer software enables NAND flash memory cards
and USB drives to look like a regular disk drive to the operating system.
FeRAM
Can hold data in memory even when the power is disconnected and
offers the higher speed of SDRAM.
PCM
Phase Change
Memory
One of a number of new memory technologies that may eventually
replace flash memory.
MRAM
Magnetoresistive random
access memory
A nonvolatile random access memory chip based on magnetic
polarization that reads and writes data faster than flash memory.
Table 3.2
RAM comes in many varieties. Static Random Access Memory (SRAM) is byte-
addressable storage used for high-speed registers and caches. Dynamic Random Access
Memory (DRAM) is byte-addressable storage used for the main memory in a computer.
Double Data Rate Synchronous Dynamic Random Access Memory (DDR SDRAM) is an
improved form of DRAM that effectively doubles the rate at which data can be moved in
and out of main memory. Other forms of memory include DDR2 SDRAM and DDR3
SDRAM.
Read-only memory (ROM) , another type of memory, is nonvolatile, meaning that its
contents are not lost if the power is turned off or interrupted. ROM provides permanent
storage for data and instructions that do not change, such as programs and data from the
computer manufacturer, including the instructions that tell the computer how to start up
when power is turned on.
Types of Memory Chips
read-only memory (ROM)
A nonvolatile form of memory.
 
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