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Banks |
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A unit of computer memory of a size
determined by the system CPU. A bank
may consist of one or more memory modules.
Processors with 64-bit bus widths will
require 64-bits of data to be sent
on the system bus. |
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Bank
Schema |
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A way to diagram memory using rows
and columns that represent memory sockets
on a computer board. Rows indicate
independent sockets and columns represent
banks. |
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Bits |
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The smallest unit of information
processed by a computer. In binary
sequences, a bit of information is
stored as a “1” or a “0.” |
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Bytes |
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In most computer systems, a byte
is a unit of data that is eight binary
digits long. A byte is the unit most
computers use to represent a character
such as a letter, number, or typographic
symbol (for example, "g", "5",
or "?"). A byte can also
hold a string of bits that need to
be used in some larger unit for application
purposes. For example, the stream of
bits, which constitute a visual image
for a program, that displays images
or the string of bits that constitutes
the machine code of a computer program).
In some computer systems, four bytes constitute a word, a unit that a computer
processor can be designed to handle efficiently as it reads and processes
each instruction. Some computer processors can handle two-byte or single-byte
instructions.
A byte is abbreviated with a "B". (A bit is abbreviated with
a small "b".) Computer storage is usually measured in byte multiples.
For example, a 256MB hard drive holds a nominal 256 million bytes - or
megabytes - of data. Byte multiples are based on powers of 2 and commonly
expressed as a "rounded off" decimal number. For example, one
megabyte ("one million bytes") is actually 1,048,576 (decimal)
bytes. (Confusingly, however, some memory manufacturers and dictionary
sources state that bytes for computer storage should be calculated as powers
of 10 so that a megabyte really would be one million decimal bytes.) |
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CAS |
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Column Address Strobe: In computer
memory technology, CAS (column address
strobe) is a signal sent to a dynamic
random access memory (DRAM) that tells
it that an associated address is a
column address. A data bit in DRAM
is stored in a cell located by the
intersection of a column address and
a row address. A RAS (row address strobe)
signal is used to validate the row
address. |
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CAS
Latency |
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In a computer system, latency is
often used to mean any delay or waiting
that increases real or perceived response
time beyond the response time desired.
Specific contributors to computer latency
include mismatches in data speed between
the microprocessor and input/output
devices and inadequate data buffers.
Within a computer, CAS latency refers
to the delay for CAS to occur. |
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DDR |
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Double Data-Rate (DDR)
memory is widely deployed and prevalent
in the computer industry. DDR memory
is an advancement of SDRAM. Whereas
SDRAM moves information in/out on the
rising edge of the clock signal, DDR
memory reads/writes data on both the
rising and falling edge of the clock
cycle, effectively doubling memory
data rates. In example, if SDRAM has
a data rate of 133MHz, corresponding
DDR memory transfers data at 266MHz. |
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Double
Data Rate 2 (DDR2) memory |
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Unigen offers the UGExD6646JL/R Family
of Micro DIMM DDR memory modules for
the space requirements of smaller form-factor,
high-speed CPU devices. These 172 pin
gold contact modules offer 64MB or
128MB of un-buffered storage for PC1600
through PC3200 applications for use
in 100MHz to 200Mhz enabled busses
and CAS latencies of 2.0, 2.5, and
3.0.
The double-sided modules support automatic and self-refresh modes, serial
detection with an EEPROM, and 4K refresh rates. The JL packages are 1.180” in
height and JR packages are 0.980” tall. |
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DIMM |
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Dual In-line Memory Modules (DIMM)
are the next evolution in embedded
memory modules. DIMMs appear similar
in size and shape to SIMMs however
the primary difference is the metal
leads on either side of a DIMM are
not tied together electrically, they
are electrically independent.
DIMMs are populated with memory that is synchronized with the CPU clock
cycles. This memory may be SRAM, SDRAM, or Nand Flash RAM. Synchronization
of memory and CPU speeds saves time in accessing memory and increases efficiency
for command execution and data transmission increasing overall system performance.
The DIMM offers two main advantages: ease of installation and due to vertical
mounting capabilities, minimal consumption of board surface. A DIMM may
have as few as 100 or as many as 232 pins. The contacts on either side
of the PCB allow for twice the amount of electrical connections over that
of a SIMM. |
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µDIMM |
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Micro Dual In-Line Memory Modules
(?DIMM) are used for the space requirements
of smaller form-factor, high-speed
CPU devices. They are similar to DIMMs
however are both shorter in height
and narrower in width than SODIMM and
DIMM modules.
?DIMMs are populated with memory that is synchronized with the CPU clock
cycles. This memory may be SRAM, SDRAM, or Nand Flash RAM. Synchronization
of memory and CPU speeds saves time in accessing memory and increases efficiency
for command execution and data transmission increasing overall system performance. |
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DRAM |
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Dynamic Random Access Memory: Dynamic
random access memory (DRAM) is the
most common kind of random access memory
(RAM) for personal computers and workstations.
Memory is the network of electrically
charged points in which a computer
stores quickly accessible data in the
form of 0s and 1s. Random access means
that the PC processor can access any
part of the memory or data storage
space directly rather than having to
proceed sequentially from some starting
place. DRAM is dynamic in that, unlike
static RAM (SRAM), it needs to have
its storage cells refreshed or given
a new electronic charge every few milliseconds.
Static RAM does not need refreshing
because it operates on the principle
of moving current that is switched
in one of two directions rather than
a storage cell that holds a charge
in place. Static RAM is generally used
for cache memory, which can be accessed
more quickly than DRAM.
DRAM stores each bit in a storage cell consisting of a capacitor and a
transistor. Capacitors tend to lose their charge rather quickly; thus,
the need for recharging. A variety of other RAM interfaces to the computer
exist (EDO/FPM and SDRAM). |
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ECC |
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Error Checking and Correction: ECC
(either "error correction [or
correcting] code" or "error
checking and correcting") allows
data that is being read or transmitted
to be checked for errors and, when
necessary, corrected on the fly. It
differs from parity checking in that
errors are not only detected but also
corrected. ECC is increasingly being
designed into data storage and transmission
hardware as data rates (and therefore
error rates) increase. |
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EDO |
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Extended Data Output: EDO (extended
data output) RAM is a type of random
access memory (RAM) chip that improves
the time to read from memory on faster
microprocessors such as the Intel Pentium.
EDO shortens the Read cycle between
the Memory and the Central Processing
Unit, dramatically increasing throughput.
EDO chips allow the Central Processing
Unit to access Memory 10 to 20 percent
faster. EDO DRAMs hold the data valid
even after the signal that "strobes" the
column address goes inactive. The EDO
scheme allows for faster Central Processing
Unit's to manage time more efficiently. |
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EEPROM |
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Electronic Erasable Programmable
Read Only Memory: user-modifiable read-
only memory (ROM) that can be erased
and reprogrammed (written to) repeatedly
through the application of higher than
normal electrical voltage. Unlike EPROM
chips, EEPROMs do not need to be removed
from the computer to be modified. However,
an EEPROM chip has to be erased and
reprogrammed in its entirety, not selectively.
It also has a limited life - that is,
the number of times it can be reprogrammed
is limited to tens or hundreds of thousands
of times. In an EEPROM that is frequently
reprogrammed while the computer is
in use, the life of the EEPROM can
be an important design consideration. |
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EPROM |
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Electronic Programmable Read Only
Memory: EPROM (erasable programmable
read-only memory) is programmable read-only
memory (programmable ROM) that can
be erased and re-used. Erasure is caused,
by shining intense ultraviolet light
through a window that is designed into
the memory chip. |
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SIMM |
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Single In-line Memory Modules (SIMM)
are the standard in embedded memory
modules. They are comprised of a printed
circuit board with affixed memory devices
(DRAM) and gold or tin/lead contacts
or connection pads. A SIMM plugs into
a computer memory expansion socket(s).
SIMMs are populated with memory that is synchronized with the CPU clock
cycles. This memory may be SRAM, SDRAM, or Nand Flash RAM. Synchronization
of memory and CPU speeds saves time in accessing memory and increases efficiency
for command execution and data transmission increasing overall system performance.
The SIMM offers two main advantages: ease of installation and due to vertical
mounting capabilities, minimal consumption of board surface. A SIMM may
have as few as 30 or as many as 200 pins. On a SIMM, the contacts on either
side of the board are electrically conjoined. |
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SODIMM |
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Small Outline Dual In-Line Memory
Modules (SODIMM) are smaller size versions
of a standard DIMM. They are similar
in all other aspects to the DIMM. Overall,
the length of a SODIMM is roughly ½ that
of the DIMM.
SODIMMs are typically offered with 72, 144, or 200-pin count connections.
SODIMMs are populated with memory that is synchronized with the CPU clock
cycles. This memory may be SRAM, SDRAM, or Nand Flash RAM. Synchronization
of memory and CPU speeds saves time in accessing memory and increases efficiency
for command execution and data transmission increasing overall system performance. |
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