Transcript 236601 - Coding and Algorithms to Memories

Welcome to
236601 - Coding and
Algorithms to Memories
1
Overview
• Lecturer: Eitan Yaakobi
[email protected], Taub 638
• Lectures hours: Thur 12:30-14:30 @ Taub 8
• Course website:
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%)
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What is this class about?
•
•
•
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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
You do not really understand something unless
you can explain it to your grandmother
4
One of the focuses during this class:
How to ask the right questions, both as
a theorist and as a practical engineer
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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…
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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
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The Evolution of Memories
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The Evolution of Memories
One Song
14% of
28% of
140 Songs
One Song One Song
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
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History
• 1961,1969 - David Paul Gregg from Gauss
Electrophysics has patented an analog optical disc
for recording video
• MCA acquires Gregg’s 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
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Optical Disc
Information is stored as pits and lands (corres. to –1,+1)
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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
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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
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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 Beethoven’s ninth symphony
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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
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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
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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
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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%
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3 Generations of Optical Recording
Blu-Ray Disc
CD
DVD
0.65 GByte
1.2 mm substrate
l = 650 nm
NA = 0.6
4.7 GBytes
4.7 GByte
0.6 mm substrate
BD
l = 405 nm
NA = 0.85
22.5 GBytes
25 GByte
0.1 mm substrate
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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
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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
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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
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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
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The Magnetic Hard Disk Drive
Spindle
motor
Arm
Disk
Read-Write
Head
Actuator
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But What is This?
A 1975 HDD Factory Floor
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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 GB’s!
• The total selling price of all of the drives shown on
this floor was about $4,000,000!
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1980’s: 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 1980’s, IBM sold billions of dollars of
these drives each year.
• It is the 2nd most profitable product ever
manufactured by man.
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IBM 3380
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1980’s: IBM 3380 Drive
One Disk
From Drive
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Q: What’s Inside an Old 4GB Nano?
A 4 GB 1”
“Microdrive”
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Disk Drive Basics
Disk Drive
Rotating Thin Film Disk
Suspended
MR Head
Track width
A Recording Track
“1”
“0”
Slider/ MR Head
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Disk Drive Basics - Writing
Head on slider
Track
Suspension
MR Read Sensor
Write Head
Shield
Recording Media
Magnetic flux leaking
from the write-head
gap records bits in the
magnetic medium
B
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Disk Drive Basics - Reading
Head on slider
Track
Suspension
MR Read Sensor
Write Head
Shield
Recording Media
Resistance of MR
read sensor changes
in response to fields
produced by the
recorded bits
B
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Magnetic Write Process
Gap is 100 nm but bits are 25 nm.
How can this be??
100 nm
100 nm
disk
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Scaling
L
L/s
 Shrink everything by factor s (including currents and microstructure).
 Areal density of data increases by the factor s2.
Shrink
Whateverything
is needed? (including microstructure)
 Requires
vastly improved
and disk
materials.
Requires
vastly head
improved
processes
 Requires improved mechanical tolerances.
Signal to noise drops
Scaling the flying height is a real challenge.
 Requires improved signal processing schemes because the
SNR drops by a factor of s.
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Fundamental Innovations
MR/GMR sensors
(1991/1997)
AFC media
(2001)
Mrteff = Mrt(1) – Mrt(2)
to 100 Gb/in2
GMR read
sensor
Perpendicular recording
(2006)
to 500+ Gb/in2
Perpendicular
media
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Longitudinal vs. Perpendicular
Longitudinal recording:
horizontal orientation
Perpendicular recording:
vertical orientation
(introduced commercially in 2005)
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Areal Density Increase of
Hard Disk Drives
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density [Mbits/in2]
Areal
Areal density, Mbits/in2
10
8
Perpendicular
recording
6
~ slow down
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1st
4
GMR head
~ 100 % CAGR
1st MR head
10
2
1st Thin film head
~ 60 % CAGR
*
10
0
250 million
fold increase !!
~ 36 % CAGR
10
-2
1st RAMAC
-4
10
1950
1960
* CAGR = Cumulative Annual Growth Rate
1970
1980
Product Year
1990
2000
2010
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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 it’s 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
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Future Technology?
GMR
laser
write coils
HAMR-Heat Assisted
Magnetic Recording
heat spot
Patterned Media
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Patterned Media
Ordinary Media
grains/bit
Patterned Media Many
One grain/bit
In patterned media, the pattern of islands is defined by lithography.
An areal density of 1 Tb/in2 requires 25-nm bit cells. Presently, this is very
difficult to achieve.
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Flash Memories
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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
3
2
1
0
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Cell programming
01
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Block erasure
10
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Gartner & Phison
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Fast
Low Power
~105 P/E Cylces
Reliable
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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
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Multi-Level Flash Memory Model
• Array of cells, made of floating gate
transistors
– Each cell can store q different values.
– Today, q typically ranges between 2 and 16.
q-1.
.
.
3210-
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Multi-Level Flash Memory Model
• Array of cells, made of floating gate
transistors
─
─
─
─
Each cell can store q different values.
Today, q typically ranges between 2 and 16.
The cell’s 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
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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 ~104-105 erasures
before it becomes unreliable
• The Goal: Representing the data efficiently
such that block erasures are postponed as
much as possible
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SLC, MLC and TLC Flash
High Voltage
High Voltage
High Voltage
011
01
SLC
Flash
0
1 Bit Per Cell
2 States
MLC
Flash
2 Bits Per
Cell
4 States
00
10
1
11
Low Voltage
Low Voltage
TLC
Flash
3 Bits Per
Cell
8 States
010
000
001
101
100
110
111
Low Voltage
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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 0
page 1
page 2
page 3
page 4
page 5
.
.
.
.
.
.
page 62
page 63
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Flash Memory Structure
• 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 MSB’s constitute one
page and all the LSB’s constitute another page
Row
index
LSB of
first 214
cells
page 4
page 8
page 12
page 16
MSB of
last 214
cells
page 1
page 3
page 7
page 11
LSB of last
214 cells
0
1
2
3
MSB of
first 214
cells
page 0
page 2
page 6
page 10
⋮
⋮
⋮
⋮
⋮
30
31
page 118
page 122
page 124
page 126
page 119
page 123
page 125
page 127
MSB/LSB
01
00
10
11
page 5
page 9
page 13
page 17
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Flash Memory Structure
Row
index
MSB Page CSB Page LSB Page
0
1
2
3
4
MSB of
first 216
cells
page 0
page 2
page 4
page 8
page 14
⋮
⋮
62
63
64
65
page
page
page
page
MSB Page CSB Page LSB Page
CSB of
first 216
cells
LSB of
first 216
cells
page 6
page 10
page 16
page 22
page 12
page 18
page 24
page 30
MSB of
last 216
cells
page 1
page 3
page 5
page 9
page 15
⋮
⋮
CSB of
last 216
cells
LSB of
last 216
cells
page 7
page 11
page 17
page 23
page 13
page 19
page 25
page 31
⋮
362 page 370 page 378 page 363 page 371 page 379
368 page 376
page 369 page 377
374 page 382
page 375 page 383
380
page 381
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Raw BER Results
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BER per page for MLC block
MSB/LSB
×10-3
Pages, colored the same,
behave similarly
01
00
10
11
×105
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Raw BER Results
High Voltage
011
010
000
001
101
100
110
111
Low Voltage
67
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