Welcome to
236601 - Coding and
Algorithms for Memories
1
Overview
• Lecturer: Eitan Yaakobi
yaakobi@cs.technion.ac.il, Taub 638
• Lectures hours: Weds 10:30-12:30 @ Taub 8
• Course website:
http://webcourse.cs.technion.ac.il/232601/Winter2015/
• Office hours: Weds 17:30-18:30 and/or other times
(please contact by email before)
• Final grade:
– Class participation (10%)
– Homeworks (50%)
– Take home exam/final Homework + project (40%)
2
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
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
5
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
1956: IBM RAMAC
5 Megabyte Hard Drive
A 2015 3 Terabyte Drive
7
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?
8
9
Some of the main goals in designing a
computer storage:
Price
Capacity (size)
Endurance
Speed
Power Consumption
10
The Evolution of Memories
11
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
12
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
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
14
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
Optical Disc
Information is stored as pits and lands (corres. to –1,+1)
16
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
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
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
19
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
20
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
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
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
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
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
25
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
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
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
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
The Magnetic Hard Disk Drive
Spindle
motor
Arm
Disk
Read-Write
Head
Actuator
30
What is This?
A 1975 HDD 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!
31
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
of$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
32
1980’s: IBM 3380 Drive
One Disk
From Drive
33
Q: What’s Inside an Old 4GB Nano?
A 4 GB 1”
“Microdrive”
34
Disk Drive Basics
Disk Drive
Rotating Thin Film Disk
Suspended
MR Head
Track width
A Recording Track
“1”
“0”
Slider/ MR Head
35
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
36
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
37
Magnetic Write Process
Gap is 100 nm but bits are 25 nm.
How can this be??
100 nm
100 nm
disk
38
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
head andprocesses
disk materials
Requires
vastly improved
 Requires
improved
mechanical
Signal
to noise
drops tolerances
Scaling the flying height is a real challenge
 Requires improved signal processing schemes because the
SNR drops by a factor of s
39
Fundamental Innovations
MR/GMR sensors
(1991/1997)
AFC media
(2001)
Mrteff = Mrt(1) – Mrt(2)
GMR read
sensor
to 100 Gb/in2
Perpendicular recording
(2006)
to 500+ Gb/in2
Perpendicular
media
40
Longitudinal vs. Perpendicular
Longitudinal recording:
horizontal orientation
Perpendicular recording:
vertical orientation
(introduced commercially in 2005)
41
Areal Density Increase of
Hard Disk Drives
10
density [Mbits/in2]
Areal
Areal density, Mbits/in2
10
8
Perpendicular
recording
6
~ slow down
10
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
42
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
43
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
44
Future Technology?
GMR
laser
write coils
HAMR-Heat Assisted
Magnetic Recording
heat spot
Patterned Media
45
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/in2 requires 25-nm bit cells. Presently, this is
very difficult to achieve
46
Flash Memories
47
48
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
49
Flash Memory Cell
3
2
1
0
50
Cell programming
01
51
Block erasure
10
52
Gartner & Phison
53
Fast
Low Power
~104 P/E Cylces
Reliable
54
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
55
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-
56
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
57
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
58
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
59
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
60
•
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
61
Row
index
MSB 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
Flash Memory
Structure
CSB Page LSB Page MSB Page CSB 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
page 7
page 11
page 17
page 23
LSB Page
LSB of
last 216
cells
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
62
Raw BER Results
63
BER per page for MLC block
MSB/LSB
×10-3
Pages, colored the same,
behave similarly
01
00
10
11
×105
64
Raw BER Results
High Voltage
011
010
000
001
101
100
110
111
Low Voltage
65
66