|
bandwidth
The capacity to move data on an electronic line such as a bus or a channel.
In short, the amount of data moved relative to a specific time frame. It
is expressed in bits, bytes, or Hertz (cycles) per second.
bank schema
A method of diagramming memory configurations. The bank schema system
consists of rows and columns that represent memory sockets on a system:
rows indicate independent sockets and columns represent banks of sockets.
binary
A method of encoding numbers as a series of bits. The binary number system,
also referred to as base 2, uses combinations of only two digits - 1
and 0.
bit
The smallest unit of information a computer processes. A bit can have a
value of either 1 or 0.
bus
The central communication avenue in a PCs system board. It normally
consists of a set of parallel wires or signal traces that connect the
CPU, the memory, all input/output devices, and peripherals.
byte
A unit of information made up of 8 bits. The byte is the fundamental
unit of computer processing; almost all aspects of a computer's
performance and specifications are measured in bytes or multiples
thereof (such as kilobytes or megabytes).
cache memory
Also known as cache RAM; a small, high-speed memory device located between
the CPU and the system DRAM. Cache is designed to supply the processor with
the most frequently requested instructions and data. Cache memory can be
three to five times faster than system DRAM.
composite
A term created by
AppleŽ Computer, Inc. that describes a memory module that uses older 4-Mbit
technology. For a given capacity, a composite module will have more chips
than a noncomposite module.
CPU
(Central Processing Unit)--The chip in a computer that has primary
responsibility for interpreting commands and running programs. The
CPU is the most vital component of a computer system.
credit card memory
A type of memory typically used in laptop and notebook computers.
Credit card memory features a small for factor and is named for its
similarity to the size of credit card.
DDR
(Double Data Rate) or SDRAM II--The next generation of the current SDRAM.
DDR finds its foundations on the same design core of SDRAM, yet adds
advances to enhance its speed capabilities. As a result, DDR allows
data to be read on both the rising and the falling edge of the clock,
delivering twice the bandwidth of standard SDRAMS. DDR essentially
doubles the memory speed from SDRAMS without increasing the clock
frequency
DIMM
(Dual In-line Memory Module)--A printed circuit board with gold or
tin/lead contacts and memory devices. A DIMM is similar to a SIMM, but
with this primary difference: unlike the metal leads on either side of
a SIMM, which are "tied together" electrically, the leads on either side
of a DIMM are electrically independent.
DIP
(Dual In-line Package)--A form of DRAM component packaging. DIPs can be
installed either in sockets or permanently soldered into holes extending
into the surface of the printed circuit board. The DIP package was
extremely popular when it was common for memory to be installed directly on
a computer's motherboard.
DRAM
(Dynamic Random Access Memory)--The most common form of system memory
packaging. DRAM can hold a charge (that is, data) for only a short period
of time. Therefore, to retain the data, it must be refreshed periodically.
If the cell is not refreshed, the data is lost.
ECC
(Error Correction Code)--An electronic method of checking the integrity
of data stored in DRAM. ECC is a more elaborate error-detection method
than parity; it can detect multiple-bit errors and can locate and fix
single-bit errors. ECC usually uses three additional bits per byte of data
(compared to one additional bit for parity).
EDO
(Extended Data Out)--A form of DRAM technology that shortens the read cycle
between memory and CPU. On computer systems designed to support it, EDO
memory allows a CPU to access memory 10 to 20 percent faster than
comparable fast-page mode chips.
EOS
(ECC on SIMM)--A data-integrity checking technology designed by IBM that
features ECC data-integrity checking built onto a SIMM.
even parity
A type of data integrity checking where the parity bit checks for an even
number of I's.
fast-page mode
A common DRAM data-access scheme. Accessing DRAM is similar to finding
information in a book. First, you turn to a particular page, then you select
information from the page. Fast-page mode enables the CPU to access new data
in half the normal access time, as long as it is on the same page as the
previous request.
gigabyte
Approximately 1 billion bytes: 1 byte x 10243
(that is, 1,073,741,824 bytes).
IC
(Integrated Circuit)--An electronic circuit-consisting of components
and connectors-contained on a semiconductor chip. Usually packaged in
a plastic or ceramic case with external connector pins.
kilobit
Approximately one thousand bits: 1 bit x 210
(that is, 1,024 bits).
kilobyte
Approximately one thousand bytes: 1 byte x 210
(that is, 1,024 bits).
logic board
(see motherboard)
megabit
Approximately one million bits: 1 bit x 1,0242
(that is, 1,048,576 bits).
megabyte
Approximately one million bytes: 1 byte x 1,0242 (that is, 1,048,576 bytes).
memory
The term commonly used to refer to a computer system's random access
memory (see also RAM). The term memory has also been used to refer to
all types of electronic data storage (see storage). A computer system's
memory is crucial to its operation; without memory, a computer could not
read programs or retain data. Memory stores data electronically in memory
cells contained in chips. The two most common types of memory chips are
DRAM and SRAM.
memory bank
A logical unit of memory in a computer, the size of which is determined
by the computer's CPU. For example, a 32-bit CPU calls for memory banks
that provide 32 bits of information at a time.
memory controller
The interface between system memory and the central processing unit.
The memory controller consists of special circuitry--usually a
microprocessor--within a computer system that interprets requests from the
central processing unit in order to locate data locations, or addresses, in
memory.
motherboard
Also known as logic board, main board, or system board; your computer's
main electronics board, which in most cases either contains all CPU,
memory, and I/0 functions, or has expansion slots that support them.
nanosecond
(ns)--One billionth of a second. Memory data access times are measured in
nanoseconds. For example, memory access times for typical 30- and 72-pin
SIMM modules range from 60 to 100 nanoseconds.
noncomposite
A term created by Apple Computer, Inc. that describes a memory module
which uses 16-Mbit technology. For a given capacity, a noncomposite
module will have fewer chips than a composite module.
odd parity
A type of data integrity checking where the parity bit checks for an odd
number of 1's.
parity
A method of data integrity checking that adds a single bit to each byte
of data. The parity bit is responsible for checking for errors in the
other 8 bits.
PC 100
In roughly the middle of 1998, Intel will introduce the BX chip set to
their motherboard designs. One element in this new architecture will include
an increase in the PC main memory bus speed (Host bus) from 66 to 100 MHz,
called PC 100. To match the 100MHz bus speed, 100MHz SDRAM modules will be
the required memory technology for this new chip set.
PCB
(Printed Circuit Board)--A component made up of layers of copper and
fiberglass; the surface of a PCB features a pattern of copper lines, or
"traces," that provide electrical connections for chips and other components
that mount on the surface of the PCB. Examples: motherboard, SIMM, credit
card memory, and so on.
PC Card
(PCMCIA: Personal Computer Memory Card International Association)--A
standard that allows interchangeability of various computing components
on the same connector. The PCMCIA standard is designed to support input/output
devices, including memory, fax/modem, SCSI, and networking products.
proprietary memory
Memory that is custom-designed for a specific computer
RAM
(Random Access
Memory)--A configuration of memory cells that hold data for processing by a
computer's central processing unit, or CPU; (see also memory). The term
random derives from the fact that the CPU can retrieve data from any
individual location, or address, within RAM.
refresh
An electrical process used to maintain data stored in DRAM. The process
of refreshing electrical cells on a DRAM component is similar to that of
recharging batteries. Different DRAM components call for different
refresh methods.
refresh rate
A specification determined by the number of rows on a DRAM component
that must be refreshed. Two common refresh rates are 2K and 4K.
self refresh
A memory technology that enables DRAM to refresh on its own-independent
of the CPU or external refresh circuitry. This technology is built into
the DRAM chip itself and reduces power consumption dramatically. It is
commonly used in notebook and laptop computers.
SIMM
(Single In-line Memory Module)--A printed circuit board with gold or
tin/lead contacts and memory devices. A SIMM plugs into a computer's
memory expansion socket. SIMMS offer two main advantages: ease of
installation and minimal consumption of horizontal surface area. A
vertically mounted SIMM requires only a fraction of the space required
by horizontally mounted DRAM. A SIMM may have as few as 30 or as many as
200 pins. On a SIMM, the metal leads on either side of the board are
electrically "tied together."
SIMM socket
A component mounted on the system board, or motherboard, designed
to hold a single SIMM.
SO DIMM
(Small Outline Dual In-line
Memory Module)--An enhanced version of a standard DIMM. The small outline DIMM
is about half the length of a typical 72-pin SIMM.
SOJ
(Small Outline J-lead)--A common form of surface-mount DRAM packaging.
It is a rectangular package with J-shaped leads on the two long sides of
the device.
storage
A medium designed to hold data, such as a hard disk or CD-ROM.
SDRAM
(Synchronous DRAM)--A DRAM technology that uses a clock to synchronize
signal input and output on a memory chip. The clock is coordinated
with the CPU clock so the timing of the memory chips and the timing of
the CPU are "in synch." Synchronous DRAM saves time in executing commands
and transmitting data, thereby increasing the overall performance of the
computer. SDRAM allows the CPU to access memory approximately 25 percent
faster than EDO memory.
SLDRAM (Synclink)
SLDRAM is a "joint effort" DRAM that may be the closest speed competitor
with Rambus. Development is coordinated through a consortium of twelve
DRAM manufactures and system companies. SLDRAM is an enhanced and faster
line extension of SDRAM architecture that extends the current four-bank
design to 16 banks. SLDRAM is currently in the development stage and is
scheduled for production is 1999.
system board
(see motherboard)
TSOP
(Thin Small Outline Package)--A type of DRAM package that uses gullwing
shaped leads on both sides. TSOP DRAM mounts directly on the surface of
the printed circuit board. The advantage of the TSOP package is that it
is one-third the thickness of an SOJ package. TSOP components are
commonly used in small outline DIMM and credit card memory applications.
|
