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Access time:
Time interval characteristic of a storage device that measures how
long it takes to communicate to that device. For hard disk drives,
access time is determined by the sum of the spin-up time, seek
time, rotational delay and transfer time.
ABL (All Bit Line):
ABL (All Bit Line) memory was introduced by SanDisk at ISSCC 2008
as a significantly faster memory than "conventional" memory. While
conventional memory uses, for actual operations, every other cell
along a selected world line (WL), this design simultaneously
exercises them all. A performance improvement of at least 100% is
derived from this all bit line (ABL) architecture relative to
conventional chips. Additional techniques push performance to even
higher levels.
Angstrom (Å):
Unit of linear measure equal to one ten billionth of a meter. The
diameter of a human hair measures about 750,000 Å.
Array:
In lithography, repetitive patterns on a die, such as an array of
memory cells.
ATA 8 standard:
ATA-8 standard is designed to support the Data Set Management
command. This command is the key in enabler to the TRIM feature
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Bad block:
A block that was manufactured with defects or has become unusable
over time.
Bad block management:
A metholodogy that marks and isolates bad blocks so that they are
not used. Bad block management stores data intended for bad blocks
in spare blocks.
Bit:
A single basic unit of information.
Block:
A physical division of a message that is made up of a sequence of
bytes or bits having a nominal size (block length) for message
transfer purposes. Dividing/Addressing data in blocks is almost
universally employed when storing data to 9-track magnetic tape, to
rotating media such as floppy disks, hard disks, optical discs and
to NAND flash memory. In NAND flash, a block defines the smallest
erase unit. In a hard disk drive, a block is the intersection of a
track and a sector. Its address is specified by providing the
number of the cylinder, head and sector (CHS).
Boron:
A chemical element with atomic number 5 used for p-channel doping
of silicon.
Byte:
A unit of data composed of 8 bits.
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Channel:
A conduit for current flow in a MOSFET between the n-type or p-type
semiconductor material.
Charge trap memory transistor:
Stores charge (electrons) in a floating gate.
Circuit:
The combination of electrical elements & components to enable a
particular function.
Cleanroom:
A closed area used in manufacturing with a defined class that
limits contamination levels and controls humidity, temperature and
particles in the air.
CMOS (Complementary Metal Oxide
Semiconductor):
A fabrication process that incorporates p-channel and n-channel
MOS transistors within the same silicon substrate.
Crystal:
A homogenous solid formed by a repeating, three-dimensional pattern
of atoms, ions, or molecules and having fixed distances between
constituent parts, often characterized by external planar
faces.
Cylinder:
All tracks accessible on a hard disk drive without moving the
head.
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Data reliability
The ability of a system or component to perform required functions
under stated conditions for a specified period of time. Special
tests (qualification) are performed to predict performance over the
lifecycle of a product.
Data retention:
The maximum period of time that written data can reliably be
retrieved from the non-volatile memory.
Defect:
A chemical or structural irregularity in a crystal that degrades
the ideal crystal structure or the films built over the wafer.
Die:
A combination of integrated circuits with defined functionality,
hundreds of which are printed on a silicon wafer. A bare die is
unpackaged.
Dielectric:
An insulator used to describe nonmetals and their interaction with
electric, magnetic or electromagnetic fields, including the storage
of electric and magnetic energy and its dissipation. Many phenomena
in electronics, solid state and optical physics can be described
using the underlying assumptions of dielectrics.
Disturb error:
Reverses the value of a bit during a Read or Write operation.
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EEPROM (Electrically Erasable Programmable Read Only
Memory):
This is early version of non-volatile memory.
Encapsulation:
The process of packaging a die with circuitry for mechanical and
environmental protection.
Endurance:
The number of Write/Erase cycles that flash memory can perform
without jeopardizing data reliability.
EPROM (Erasable Programmable Read Only
Memory):
This is an early version of non-volatile memory.
Error Detection/Correction Code (EDC/ECC)
Detects errors and corrects them by reconstructing the original
data using extra bits, and increases data retention.
Etching:
A micro fabrication technique to chemically remove layers from the
surface of a wafer during manufacturing. Etching is a critically
important process that is performed repeatedly on a wafer in many
steps with the aim of achieving a minimal number of defects. Part
of the wafer is protected from the etchant by using a mask that
resists etching. In some cases, the mask is photo resist for use in
patterning by photolithography. In other cases, silicon nitride is
used, which is a more robust material
ExtremeFFS™*(Extreme Flash
File System)
ExtremeFFS™* technology has the potential to accelerate
random write performance thus extend the endurance of SanDisk G3
SSDs inside PCs that use operating systems such as Windows XP and
Windows 7 ExtremeFFS applies a novel approach to flash management
based on design elements such as:
- Page-based algorithm: ExtremeFFS uses a
page-based algorithm with no fixed coupling between physical and
logical location. This gives SanDisk® SSD the freedom to store a
sector of written data where it is most convenient and
efficient.
- Fully non-blocking architecture: NAND channels
operate independently as required by user activities, with some
reading while others are writing and garbage collecting.
*ExtremeFFS is a SanDisk page-based flash
management algorithm, optimized for popular operating systems, has
the potential to greatly increase SSD random write speeds and
efficiency thus accelerating the performance and extending the
endurance of SSDs inside PCs
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Fab (Fabrication plant):
Semiconductor wafer manufacturing facilities.
Flash Memory:
A non-volatile semiconductor memory consisting of 1-transistor
memory architecture cells. The memory mechanism consists of storing
charge in the gate dielectric. A second gate on the transistor
enables data storage and simultaneous erasure of defined blocks of
memory electronically.
Floating gate:
Stores an electrical charge for extended periods of time even
without connection to power supply. Electrons stored in the
floating gate are sensed by the threshold voltage.
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Gate:
An electrode that regulates the current flow in a metal oxide
semiconductor (MOS) transistor.
Gate oxide:
A thin layer of pure, defect-free, thermally grown oxide. It serves
as the dielectric layer in MOSFET between the drain and source.
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Head (also called Access arm):
Writes data to/reads from the platter surface of a hard disk drive.
Each head services one side of one platter.
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Ingot:
In the semiconductor industry, a material made of silicon that is
processed to achieve single crystal silicon. This is then cut and
polished to achieve wafers on which devices ranging from
microprocessors to memory devices can be fabricated.
Input/Output Per Second (IOPS):
A measurement of the number of operations (e.g., Read or Write)
performed per second. A solid state drive achieves higher IOPS when
accessing random files than a hard disk drive.
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JEDEC (Joint Electron Device Engineering
Council)
A leading developer of standards for the solid-state industry,
comprised of over 3000 participants appointed by some 295 companies
working in 50 JEDEC committees.
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Latency:
A delay before a given operation can be performed.
Level:
A logical method to define the analog value of a bit. 1 bit
requires 2 levels.
Lithography:
An abbreviation for photolithography, a micro fabrication technique
used to design the pattern for integrated circuits and
micro-electromechanical systems. This term was modified from the
print world, either text or artwork, where lithography refers to
the use of oil or fat and gum arabic to divide the smooth surface
into regions which accept the ink, and hydrophilic regions which
reject it and thus become the background.
Logical Block Address (LBA):
An addressing scheme that numbers block linearly rather than by
cylinder, head and sector numbers (CHS). LBA generally replaces the
legacy block addressing scheme, although both are supported on
current solid state drives and hard disk drives.
LDE (Long-term Data Endurance):
A simple metrics to determine solid state drive (SSD) endurance
based on typical end-user activity. LDE was proposed by SanDisk
(submitted to JEDEC in October 2008) to enable users to compare the
data endurance of various SSD offerings. LDE measures the total
number of data writes, expressed in Terabytes that can be performed
over the SSD lifespan. SanDisk offers a methodology that enables
accelerated testing.
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Mask:
A plate of glass or quartz that contains the photographic image of
wafer patterns to define a single process layer. The mask is
exposed onto a photosensitive layer, covers a wafer surface to
expose/hide selected areas to/from various fabrication
processes.
Mean time between failures (MTBF)
The average number of time until a failure is encountered.
Mean time to failure (MTTF)
The time until the first failure is encountered. Used in systems
where the first failure is usually fatal.
Memory cell:
Intersection of bit line and word line identifies location where
data is stored.
MOSFET (Metal Oxide Semiconductor Field Effect
Transistor):
A device used to amplify or switch electronic signals. It is by far
the most common field-effect transistor in both digital and analog
circuits. A MOSFET is composed of a channel of n-type or p-type
semiconductor material
Micrometer:
A metric unit of linear measure that equals one millionth of a
meter or 10,000 angstroms.
Moore's Law:
This law, based on a prediction made in 1965, states that the
density of transistors doubles every 1½ to 2 years. It enables the
miniaturization of integrated circuits.
Multi Level Cell (MLC):
More than one bit is stored in a single cell; e.g., D2, D3, x4.
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NAND flash:
Non-volatile memory that enables sequential access to memory cells,
uses silicon more efficiently than NOR flash resulting in lower
cost per gigabit, achieves faster write speed than NOR flash,
suitable for mass data storage.
Non-volatile Memory (NVM):
A type of memory that retains data even in the absence of
power.
NOR flash:
Non-volatile memory that enables direct access to each memory cell,
uses silicon less efficiently than NAND flash resulting in higher
cost per gigabit, achieves fast random access speed but slower
write speed than NAND flash, suitable for code storage.
N-type:
A semiconductor material that has negatively charged conductivity
with an excess of electrons.
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One Time Programmable (OTP)
Memory that can only be written to once and cannot be erased, with
no read limitations.
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Page:
The smallest write unit in NAND flash.
Platter:
The spinning disk used in a hard disk drive. Data is written by the
head to the top of bottom of the platter surface.
Printed Circuit Board (PCB)
A board comprised of some specific dielectric, low-cost insulator
material to mechanically support and electrically connect
electronic components. A PCB uses conductive pathways, or traces,
etched from copper sheets laminated onto a non-conductive
substrate.
P-type:
A semiconductor material that has positively charged conductivity
with a deficiency of electrons, usually achieved by Boron
doping.
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Random access:
The ability to access all elements in a sequence with no special
order in the same amount of time.
Random access memory (RAM)
Volatile memory that can be read/written to/from arbitrary
locations in arbitrary sequence.
Reliability:
The probability that a product will perform its intended functions
within defined conditions for a specified time.
Revolutions Per Minute (RPM):
Used to measure the speed of a hard disk drive based on the number
of revolutions per minute performed by the disk.
Rotational latency:
The delay in rotation for the hard disk drive to align the required
sector beneath the head (calculated as half of the duration to
rotate the plate a full cycle).
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Sector:
A pie-shaped slice on a hard disk drive platter that contains the
minimum addressable area to/from which data can be
written/read
Seek time:
The time for the head to reach the desired track on a hard disk
drive.
Semiconductor:
A solid material with electrical conductivity characteristics that
are between conductor and insulator.
Silicon:
An element in the periodic table used to manufacture
semiconductors.
Single Level Cell (SLC):
Single bit is stored in a single cell.
Singulation:
The process of cutting a wafer into individual dies
Spin-up time :
The time required to accelerate the hard disk drive to operating
speed.
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Threshold voltage:
Senses the electrons in the floating gate, and acts as the gate
voltage to enable current to flow.
Track:
Thin, concentric circles on the platter surface of a hard disk
drive that are used to help identify the location of data.
Transistor:
A semiconductor used as an amplifier or electrically controlled
switch, and the fundamental circuitry building block in computers,
cellphones and other modern electronic devices. A transistor is
made of a semiconductor material with at least three terminals for
connection to an external circuit. Voltage or current applied to
two of the terminals changes the current flowing through another
pair of terminals. Because the controlled power can be much larger
than the controlling power, the transistor provides amplification
of a signal.
Trapped charges:
Charges trapped in the gate oxide that constitute part of the
process that enables non-volatile memory.
TRIM:
TRIM contributes to a substantial gain in the product performance,
by informing the SSD of the unused media space and allowing it to
continuously manage its resources and retain optimized performance
throughout its lifespan.
Tunneling:
A physical phenomena where electrons move across an insulating
layer or a gap between two conductors. Tunneling is the basis for
NAND flash write and erase operations.
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Volatile memory:
A type of memory that loses data when power is off.
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Wafer:
A thin slice with parallel faces cut from a semiconductor crystal
such as silicon. A silicon wafer is prepared from silicon
ingots.
Wear leveling:
A technology that prevents wear-out of specific blocks to extend
the lifetime of flash memory by evenly distributing data from
repeated Write/Erase cycles over the entire flash media. Wear
leveling is particularly relevant for typical file systems (ex: DOS
FAT file system) and file management algorithms that repeatedly
write/erase the identical physical locations.
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Yield:
Percentage of good dies on a wafer vs. the total number of
dies.