Glossary of memory terms

Bit
Abbreviation for binary digit, i.e. binary value. A variable that can only have one of two values, usually 0 and 1. This makes it the smallest unit of data. Is abbreviated with a lower case b. Mb are thus megabit.

bps
Abbreviation for bits per second.

Bitline
The array of columns in a memory cell field of RAM or ROM to which the stored value of a selected memory cell is transferred. The bitline is usually connected to the source of the selection transistor.

Burst mode
Also called bundle mode, a rapid data transfer technique that sends larger chunks of data. The overall data block is broken down into a continuous stream of smaller blocks. The amount of data transferred is reduced and loss cycles are minimized because the address and control information only has to be sent once at the beginning.

Bus
Several wires, usually parallel, that share a common address.

Byte
A group of 8 bits. Is abbreviated with a capital B. MB are thus megabytes.


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C

Cache
Intermediate storage for data that is necessary or could be necessary. A cache is much faster than mechanical storage media or even memory. If the cache sits between the CPU and the RAM, it is referred to as Level1 to Level3 cache (L1, L2, L3). As the number of the cache increases, it becomes larger but also slower. Data is also cached in other places like on hard drives or optical burner drives.

CAS
Abbreviation for Column Address Strobe. It is one of the control signals for a DRAM memory chip that tells the chip to accept the given address and interpret it accordingly.

CAS-Latency
The delay in clock cycles that occurs when addressing columns in DRAM.

CBR
Abbreviation for Constant Bit Rate.

Chip
A chip is a die made of doped semi-conducting material in a plastic casing. This casing protects the sensitive die from external influences and static. Contact leads go through the plastic casing from the die to the outside. Integrated circuits (ICs) are attached to the die. The size of the chip is primarily dependent on the number of transistors integrated on the die.

Column Address Strobe
Column Address Strobe is abbreviated as CAS. It is one of the control signals for a DRAM memory chip that tells the chip to accept the given address and interpret it accordingly.


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D

Data bus
Several wires, usually parallel, that share a common address.

DDR
Abk. für Double Data Rate, doppelte Datenrate.

DDR2
Refers to the second generation of DDR-SDRAMs on the market in 2004.

DDR-SDRAM
Double Data Rate - SDRAM. The first SDRAMs (PC66, PC100, PC133) only transmitted data on a single edge of the signals. Double data rate modules use both edges (rising and falling) which makes them theoretically able to transmit with twice the data speed at the same frequency. However, the amount of administrative work required causes losses.

Die
Ein Die (gesprochen Die) ist ein Plättchen aus dotiertem Halbleitermaterial, in der Regel eine Form des Siliziums. Es wird von einem Kunststoffmantel vor äußeren einflüssen geschützt. Kontakte führen vom Die durch die Hülle nach Außen. Auf dem Die sind integrierte Schaltkreise (ICs) aufgebracht. Die Größe eines Chips (Die + Kunststoffmantel + Leitungen) ist im wesentlichen abhängig von der Anzahl der auf dem Die realisierten Transistoren.

Digital
A die is a small wafer made of doped semi-conducting material, usually a type of silicon. It is protected from external influences by a plastic casing. Contact leads go through the plastic casing from the die to the outside. Integrated circuits (ICs) are attached to the die. The size of a chip (die + plastic casing + wires) is primarily dependent on the number of transistors integrated on the die.

Digital
With intermediate gradations, discontinuous, broken down into discrete phases. A digital signal, unlike an analog one, can only have specific values on a scale, usually only 0 or 1.

DIMM
Abbreviation for Dual In-Line Memory Module. Unlike SIMMs, the DIMM contact leads are not continuous. The contact leads on both sides are electrically independent, making twice the number of contacts available.

DIN
Abbreviation for both the German Institute for Standardization (Deutsches Institut für Normung) and the German Industrial Standard (Deutsche Industrienorm).

DIP
Abbreviation for Dual Inline Package. A casing for integrated circuits that has contact leads on opposite sides just like the familiar pins from old memory chips.

DMA
Abbreviation for Direct Memory Access. In addition to the CPU, DMA forms a second data channel between peripherals and the main memory that allows a peripheral device to read or write data directly without affecting the CPU.

Doping
Targeted storage of foreign atoms in semi-conducting substrates to achieve or improve specific electrical properties.

Double Word
A piece of information or command that is four bytes long (32 bits).

DRAM
Abbreviation for Dynamic Random Access Memory. DRAM is direct access memory where information is usually stored randomly as charges in a capacitor. Since all capacitors lose their charge over time, the information must be periodically (dynamically) refreshed even if nothing has changed.

Dual-Port RAM
A RAM enhancement that provides two different access channels to the storage cells of the module. This allows two units to access the information in RAM at the same time without inhibiting one another. Dual-port memory is primarily used for the video RAM of graphic adapters where the CPU and adapter logic compete for access to screen memory.

Dynamic Random Access Memory
Abbreviated with DRAM. DRAM is direct access memory where information is usually stored randomly as charges in a capacitor. Since all capacitors lose their charge over time, the information must be periodically (dynamically) refreshed even if nothing has changed.


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E

ECC
Abbreviation for Error Correction Code. A type of cyclical redundancy code where the redundancy is so high that errors are not only detected but can also be corrected. With respect to memory, this is limited to detection and automatic correction of double bit errors.

EEPROM
Abbreviation for Electrically Erasable PROM. This is an electrical read-only memory that can be erased by exposing it to a strong electrical charge

EPROM
Abbreviation for Erasable PROM. A read-only memory that can be erased by exposing it to ultraviolet light. To do this, it must be removed.


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G

Gate
The control terminal of a field effect transistor. The conductivity of the transistor can be changed by changing the voltage on the gate.

GByte - GigaByte
2 to the 30th power bytes = 1 073 741 800 bytes, not what the prefix giga usually stands for, i.e. a billion = 10 to the 9th power (1 000 000 000) bytes.


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H

Hertz
Abbreviated with Hz, unit of frequency. Measured in cycles per second. 1 Hz = 1/second.


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I

IC - Integrated Circuit
Integrated circuits are electronic semi-conducting components. They are made up of various components used to produce transistors, resistance or capacitors.

IEEE
Abbreviation for the Institute of Electrical and Electronic Engineers.

Inches
1" inch = 2.54 cm
12" (inches) = 1 (foot)
3' (feet) = 1 yard (~ 91.44 cm)


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K

K - Kilo
Represents one thousand 1kHz = 1000 Hz

Kb - Kilobit
2 to the 10th power bits = 1024 bits. Because a binary system is used in connection with memory capacities, kilo = 1000 may only be used as an approximate value with the standard decimal system.

KB - KiloByte
2 to the 10th power bytes = 1024 bytes. Because a binary system is used in connection with memory capacities, kilo = 1000 may only be used as an approximate value with the standard decimal system.


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L

L1 /2/3 - Level
Name of the fastest cache integrated directly into a CPU. Generally supported by a larger but slower L2 cache. There is often an L3 cache preceding the RAM in server and workstation CPUs.

Latency
Delays to cleanly separate consecutive commands for the system. Latencies for memory are specified in clock cycles.


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M

Main memory
The memory of a computer that stores the program and the data required to run the program or the data processed by the program. The main memory is usually DRAM, today called DDR-SDRAM.

Mb - Mbit
2 to the 20th power bit = 1 048 576 bit. Because a binary system is used in connection with memory capacities, mega = 1 000 000 may only be used as an approximate value with the standard decimal system.

MB - MByte
2 to the 20th power bytes = 1 048 576 bytes. Because a binary system is used in connection with memory capacities, mega = 1 000 000 may only be used as an approximate value with the standard decimal system.

Mb/s
Transmission rate in megabits per second.

Mikro - µ
Micro is one millionth of a specific unit
1 µm = 0.000 001 m

Memory bank
A group of memory chips that are accessed together.

Memory Mapped I/O
For Memory Mapped I/O, the registries of peripherals are found in the normal memory address space and are therefore accessed via the normal memory commands.

MMU
Abbreviation for Memory Management Unit. The MMU is either part of a processor or integrated on a separate chip. It carries out the address transformation for segmentation and paging.


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N

n - Nano
One billionth of a unit 1 nm = 0.000 000 001 m. 000 001 m.

Nibble
A group of four bits, a half byte.

NVR
Abbreviation for Non-Volatile RAM. Memory that retains its contents even after the power supply has been switched off.


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P

Page
Part of an address space that is treated as a whole.

Page Mode
An operating mode of DRAM modules that provides very fast access to the memory cells and hence, the data of a page. In Page mode, the DRAM only has to be given the column address to address data within a page; this saves time because it is not necessary to load the RAS. If the required data lies outside of the page, it is necessary to switch pages, a process that is quite time-consuming.

Paging
In general, paging refers to breaking down an address space into smaller units which are called pages.

Parity
A simple way to detect errors when recording or transmitting data. Parity works by adding a parity bit whose value is calculated from the data bits to a quantity of data. When parity is even, the total number of ones made up of data and parity bits is even, the module 2 sum of all bits equals 1. This means those that only an uneven number of errors can be detected, usually one. The parity would be identical to the original value for double bit errors.

PROM
Abbreviation for Programmable Read Only Memory. A read-only memory whose memory data is programmed in the last production step or by the user on-site but cannot be changed during operation.


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R

RAM
Abbreviation for Random Access Memory, memory with random or direct access. Data can be directly or randomly (i.e. with free selection of the data address) entered or read for RAM.

RAS - Row Access Strobe
Abbreviation for Row Access Strobe. It is one of the control signals for a DRAM memory chip that tells the chip to accept the given address as a row access address and interpret it accordingly.

RAS-Latency
The delay in clock cycles that occurs when addressing rows in DRAM.

ROM
Abbreviation for Read Only Memory. ROM refers to a memory module that can only be read from and not written to. The stored data is written once and can then no longer be changed or changed only with special devices. Data stored in ROM is retained even after the power supply is switched off.


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S

Stacked
Generally refers to a modular design where two chips are placed above one another on both sides. This makes it possible to build "larger", i.e. high-capacity modules with more affordable, lower capacity chips. One of the disadvantages, other than the width of the modules which can cause space problems as well as problems with heat, is a loss in performance as the speed adjusts to the extremely long conductors of the upper chips.

Stacked Chips
Two physically independent memory chips that are attached to another in such a way that they function as a single unit. The only take up as much room as a single chip on the board of a memory module. It must be kept in mind that this makes the model almost twice as a wide and the distance between two modules is considerably decreased. The reduced cooling can cause problems with heat.

Stacked ICs (Integrated Circuit)
This term is not actually 100 percent accurate. It is commonly used for stacked chips although a chip is already made up of a large number of ICs and they are not "stacked".

SIMM
Abbreviation for Single In-Line Memory Module. A type of memory modules with a contact terminal which plugs into a socket, similar to adapter cards.

SRAM
Abbreviation for Static RAM. SRAM is direct access memory (RAM) that usually holds each bit of memory through the state of a flip-flop. Because the activation state of the flip-flop does not change without a write signal, SRAM does not have to be refreshed like DRAM which is why it is referred to as "static". However, the large number of transistors required makes it too expensive for general use as memory.

Substrate
The support material for the microchip circuitry. The transistors and the circuit wires are generally formed on the substrate. The most common substrate material is silicon which is doped to adjust the electrical properties as needed.

Synchronous
Synchronized in phase or clock interval or using a clock signal.


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T

TB - Tbyte
A terrabyte = 2 to the 40th power, not 1 trillion bytes.

TSOP
Abbreviation for Thin Small Outline Package. A very flat casing with contact leads on both sides. TSOP cases are primarily used for Flash memory.


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U

USB
Abbreviation for Universal Serial Bus.


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V

VRAM
Abbreviation for Video RAM. More specifically, dual-port RAM modules are meant that are used for the video RAM of graphic adapters.


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W

Word
Two bytes, i.e. 16 bits.


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