Welcome to 236601 - Coding and Algorithms to Memories 1
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Overview Lecturer: Eitan Yaakobi [email protected],
Taub 638 [email protected] Lectures hours: Thur 12:30-14:30
@ Taub 8 Course website:
http://webcourse.cs.technion.ac.il/236601/Spring2014/
http://webcourse.cs.technion.ac.il/236601/Spring2014/ Office hours:
Thur 14:30-15:30 and/or other times (please contact by email
before) Final grade: Class participation (10%) Homeworks (50%) Take
home exam/final Homework + project (40%) 2
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What is this class about? Coding and Algorithms to Memories
Memories HDDs, flash memories, and other non-volatile memories
Coding and algorithms how to manage the memory and handle the
interface between the physical level and the operating system Both
from the theoretical and practical points of view Q: What is the
difference between theory and practice? 3
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You do not really understand something unless you can explain
it to your grandmother 4
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One of the focuses during this class: How to ask the right
questions, both as a theorist and as a practical engineer 5
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Memory Storage Computer data storage (from Wikipedia): Computer
components, devices, and recording media that retain digital data
used for computing for some interval of time. What kind of data?
Pictures, word files, movies, other computer files etc. What kind
of memories? Many kinds 6
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1956: IBM RAMAC 5 Megabyte Hard Drive A 2012 Terabyte Drive
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Memories Volatile Memories need power to maintain the
information Ex: RAM memories, DRAM, SRAM Non-Volatile Memories do
NOT need power to maintain the information Ex: HDD, optical disc
(CD, DVD), flash memories Q: Examples of old non-volatile memories?
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Some of the main goals in designing a computer storage: Price
Capacity (size) Endurance Speed Power Consumption 10
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The Evolution of Memories 11
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The Evolution of Memories One Song 14% of One Song 28% of One
Song 140 Songs 960 Songs 5120 Songs 6553 Songs 209,715 Songs
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Optical Storage Storage systems that use light for recording
and retrieval of information Types of optical storage CD DVD
Blu-Ray disc Holographic storage 13
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History 1961,1969 - David Paul Gregg from Gauss Electrophysics
has patented an analog optical disc for recording video MCA
acquires Greggs company and his patents 1969 - a group of
researchers at Philips Research in Eindhoven, The Netherlands, had
optical videodisc experiments 1975 Philips and MCA joined forces in
creating the laserdisc 1978 the laserdisc was first introduced but
was a complete failure and this cooperation came to its end 1983
the successful Compact Disc was introduced by Philips and Sony
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History First generation CD (Compact Disc), 700MB Second
generation DVD (Digital Versatile Disc), 4.7GB, 1995 Third
generation BD (Blu-Ray Disc) Blue ray laser (shorter wavelength) A
single layer can store 25GB, dual layer 50GB Supported by Sony,
Apple, Dell, Panasonic, LG, Pioneer 15
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Optical Disc Information is stored as pits and lands (corres.
to 1,+1) 16
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Optical Storage How does it work? A light, emitted by a laser
spot, is reflected from the disc The light is transformed to a
voltage signal and then to bits 17
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The Material of the CD Most of the CD consists of an
injection-molded piece of clear polycarbonate plastic, 1.2 mm thick
The plastic is impressed with microscopic pits arranged as a
single, continuous, extremely long spiral track of data A thin,
reflective aluminum layer is sputtered onto the disc, covering the
pits A thin acrylic layer is sprayed over the aluminum to protect
it The label is then printed onto the acrylic 18
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The Laser The laser spot, emitted by the laser diode is
reflected from the disc to the photodiode by the partially silvered
mirror When the spot is over the land: The light is reflected and
the received optical signal is high When the spot is over a pit:
The light is reflected from both the bottom of the pit and the land
The reflected lights interfere destructively and the signal is low
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The Disc A CD has a single spiral track of data, circling from
the inside of the disc to the outside The track is approximately
0.5 microns width, with 1.6 microns separating one track from the
next The pits size is at least 0.83 microns and 125 nanometers high
The length of the track after stretching it is 3.5 miles! Holds 74
minutes and 33 seconds of sound, enough for a complete mono
recording of Beethovens ninth symphony 20
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CD Player Components A drive motor - spins the disc and rotates
it between 200 and 500 rpm depending on which track is being read A
laser and a lens system for focusing read the pits A tracking
mechanism moves the laser assembly so that the laser's beam can
follow the spiral track 21
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DVD Similar to CD but has more capacity (4.7G Vs. 0.7G) DVDs
have the same diameter and thickness as CDs They are made of the
same materials and manufacturing methods The data on a DVD is
encoded in the form of small pits and lands Similar to CD, a DVD is
composed of several layers of plastic, totaling about 1.2
millimeters thick A semi-reflective gold layer is used for the
outer layers, allowing the laser to focus through the outer and
onto the inner layers 22
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The material of DVD Comparing to CD, the pits width is 320
nanometer, and at least 400 nanometer length Only 740 nanometers
separate between adjacent tracks Therefore, the DVD supplies a
higher density data storage 23
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Blu-Ray Disc The wavelength of a blue-violet laser (405nm) is
shorter than the one of a red laser (650nm) It possible to focus
the laser spot with greater precision Data can be packed more
tightly and stored in less space Blu-ray Discs holds 25 GB (one
layer) 56% 50 GB (dual layer) 44% 24
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l = 650 nm NA = 0.6 4.7 GBytes l = 405 nm NA = 0.85 22.5 GBytes
1.2 mm substrate0.6 mm substrate0.1 mm substrate CDDVDBD 0.65
GByte4.7 GByte25 GByte 3 Generations of Optical Recording Blu-Ray
Disc 25
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Holographic Storage An optical technology that allows 1 million
bits of data to be written and read out in single flashes of light
A stack of holograms can be stored in the same location An entire
page of information is stored at once as an optical interference
pattern within a thick, photosensitive optical material 26
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Holographic Storage Light from a coherent laser source is split
into two beams: signal (data-carrying) and reference beams The
Digital data is encoded onto the signal beam via a spatial light
modulator (SLM) By changing the reference beam angle, wavelength,
or media position many different holograms are recorded 27
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Data Encoding The data is arranged into large arrays The 0's
and 1's are translated into pixels of the spatial light modulator
that either block or transmit light The light of the signal beam
traverses through the modulator and is therefore encoded with the
pattern of the data page This encoded beam interferes with the
reference beam through the volume of a photosensitive recording
medium The light pattern of the image is recorded as a hologram on
the photopolymer disc using a chemical reaction 28
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Reading Data The reference beam is shined directly onto the
hologram When it reflects off the hologram, it holds the light
pattern of the image stored there The reconstruction beam is sent
to a CMOS sensor to recreate the original image 29
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The Magnetic Hard Disk Drive Disk Arm Read-Write Head Actuator
Spindle motor 30
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But What is This? A 1975 HDD Factory Floor 31
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Facts About This Factory Floor The total capacity of all of the
drives shown on this factory floor was less than 20 GBs! The total
selling price of all of the drives shown on this floor was about
$4,000,000! 32
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1980s: IBM 3380 Drive The IBM 3380 was the first gigabyte
drive. The manufacturing cost was about $5000. The selling price
was in the range $80,000- $150,000! During the 1980s, IBM sold
billions of dollars of these drives each year. It is the 2 nd most
profitable product ever manufactured by man. 33
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IBM 3380 34
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1980s: IBM 3380 Drive One Disk From Drive 35
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Q: Whats Inside an Old 4GB Nano? A 4 GB 1 Microdrive 36
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Disk Drive Basics 1 0 37
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Disk Drive Basics - Writing Track Recording Media Write Head MR
Read Sensor Shield B Head on slider Suspension Magnetic flux
leaking from the write-head gap records bits in the magnetic medium
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Disk Drive Basics - Reading Track Recording Media Write Head MR
Read Sensor Shield B Head on slider Suspension Resistance of MR
read sensor changes in response to fields produced by the recorded
bits 39
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Magnetic Write Process disk 100 nm Gap is 100 nm but bits are
25 nm. How can this be?? 100 nm 40
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Scaling Shrink everything by factor s (including currents and
microstructure). Areal density of data increases by the factor s 2.
Requires vastly improved head and disk materials. Requires improved
mechanical tolerances. Scaling the flying height is a real
challenge. Requires improved signal processing schemes because the
SNR drops by a factor of s. What is needed? 41
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Fundamental Innovations GMR read sensor Perpendicular media AFC
media (2001) MR/GMR sensors (1991/1997) to 100 Gb/in 2 to 500 +
Gb/in 2 Perpendicular recording (2006) 42
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Longitudinal vs. Perpendicular Longitudinal recording:
horizontal orientation Perpendicular recording: vertical
orientation (introduced commercially in 2005) 43
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Areal Density Increase of Hard Disk Drives * * CAGR =
Cumulative Annual Growth Rate 44
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Predicting the Future of Disk Drives It looks like the present
technology will max out in a few years As the size of the stored
bit shrinks, the present magnetic material will not hold its
magnetization at room temperature. This is called the
superparamagnetic effect A radically new system may be required
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The Future of Disk Drives Two solutions are being pursued to
overcome the superparamagnetic effect One solution is to use a
magnetic material with a much higher coercivity. The problem with
this solution is that you cannot write on the material at room
temperature so you need to heat the media to write The second
approach is called patterned media where bits are stored on
physically separated magnetic elements 46
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Future Technology? HAMR-Heat Assisted Magnetic Recording
Patterned Media 47
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Patterned Media Ordinary Media Patterned Media Many grains/bit
One grain/bit In patterned media, the pattern of islands is defined
by lithography. An areal density of 1 Tb/in 2 requires 25-nm bit
cells. Presently, this is very difficult to achieve. 48
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Flash Memories 49
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The History of Flash Memories Flash memory was introduced in
1984 by Dr. Fujio Masouka of Toshiba. Why the name flash? Because
the erase operation is similar to the flash of the camera There are
two types: NOR and NAND flash. NAND flash is used in most products
because of its cost advantage. Recently multi-level (MLC) NAND
flash has been introduced because it can store more information.
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Flash Memory Cell 1 0 3 2 52
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Cell programming 0101 53
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Block erasure 1010 54
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Gartner & Phison 55
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Fast Low Power Reliable ~10 5 P/E Cylces 56
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Solid State Drives What is a Solid State Drive (SSD)? It is an
Hard Disk with flash instead of a disk Why to use a Solid State
Drive? Lower power consumption Durability Faster random access
Flash drives have not replaced HDDs in most large storage
applications because: They wear out They are more temperature
sensitive Erasing is more difficult They are more expensive 57
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Array of cells, made of floating gate transistors Each cell can
store q different values. Today, q typically ranges between 2 and
16. 0- 1- 2- 3-.... q-1-. Multi-Level Flash Memory Model 58
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Array of cells, made of floating gate transistors Each cell can
store q different values. Today, q typically ranges between 2 and
16. The cells level is increased by pulsing electrons. Reducing a
cell level requires resetting all the cells in its containing block
to level 0 A VERY EXPENSIVE OPERATION Multi-Level Flash Memory
Model 59
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Flash Memory Constraints The lifetime/endurance of flash
memories corresponds to the number of times the blocks can be
erased and still store reliable information Usually a block can
tolerate ~10 4 -10 5 erasures before it becomes unreliable The
Goal: Representing the data efficiently such that block erasures
are postponed as much as possible 60
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SLC, MLC and TLC Flash High Voltage Low Voltage 1 Bit Per Cell
2 States SLC Flash 011 010 000 001 101 100 110 111 01 00 10 11 0 1
High Voltage Low Voltage 2 Bits Per Cell 4 States MLC Flash High
Voltage Low Voltage 3 Bits Per Cell 8 States TLC Flash 61
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Flash Memory Structure A group of cells constitute a page A
group of pages constitute a block In SLC flash, a typical block
layout is as follows page 0page 1 page 2page 3 page 4page
5............ page 62page 63 62
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In MLC flash the two bits within a cell DO NOT belong to the
same page MSB page and LSB page Given a group of cells, all the
MSBs constitute one page and all the LSBs constitute another page
Row index MSB of first 2 14 cells LSB of first 2 14 cells MSB of
last 2 14 cells LSB of last 2 14 cells 0page 0page 4page 1page 5
1page 2page 8page 3page 9 2 page 6page 12page 7page 13 3 page
10page 16page 11page 17 30page 118page 124page 119page 125 31page
122page 126page 123page 127 01 10 00 11 MSB/LSB Flash Memory
Structure 63
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Row index MSB of first 2 16 cells CSB of first 2 16 cells LSB
of first 2 16 cells MSB of last 2 16 cells CSB of last 2 16 cells
LSB of last 2 16 cells 0page 0page 1 1page 2page 6page 12page 3page
7page 13 2 page 4page 10page 18page 5page 11page 19 3 page 8page
16page 24page 9page 17page 25 4page 14page 22page 30page 15page
23page 31 62page 362page 370page 378page 363page 371page 379 63page
368page 376page 369page 377 64page 374page 382page 375page 383
65page 380page 381 MSB Page CSB Page LSB Page Flash Memory
Structure 64
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Raw BER Results 65
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66 BER per page for MLC block 10 5 10 -3 Pages, colored the
same, behave similarly 01 10 00 11 MSB/LSB
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Raw BER Results 011 010 000 001 101 100 110 111 High Voltage
Low Voltage 67