1. Welcome to 236601 - Coding and Algorithms for Memories

2. Overview Lecturer: Eitan Yaakobi yaakobi@cs.technion.ac.il, Taub 638
Lectures hours: Weds Taub 8
Course website:
Office hours: Weds 17:30-18:30 and/or other times (please contact by before)
Final grade:
Class participation (10%)
Homeworks (50%)
Take home exam/final Homework + project (40%)

3. 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?

4. You do not really understand something unless you can explain it to your grandmother

5. One of the focuses during this class: How to ask the right questions, both as a theorist and as a practical engineer

6. 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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7. A Terabyte Drive
1956: IBM RAMAC
5 Megabyte Hard Drive

8. 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?

9. Flash Memory Summit
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10. Some of the main goals in designing a computer storage:
Price
Capacity (size)
Endurance
Speed
Power Consumption
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11. The Evolution of Memories

12. 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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13. Optical Storage
Storage systems that use light for recording and retrieval of information
Types of optical storage CD
DVD
Blu-Ray disc
Holographic storage

14. History
1961, David Paul Gregg from Gauss Electrophysics has patented an analog optical disc for recording video
MCA acquires Gregg’s company and his patents
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

15. 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

16. Optical Disc
Information is stored as pits and lands (corres. to –1,+1)

17. 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

18. 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

19. 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

20. 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

21. 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

22. 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

23. 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

24. 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%

25. Blu-Ray Disc 3 Generations of Optical Recording CD DVD BD 0.65 GByte
l = 650 nm
NA = 0.6
4.7 GBytes
l = 405 nm
NA = 0.85
22.5 GBytes
0.65 GByte
4.7 GByte
25 GByte
1.2 mm substrate
0.6 mm substrate
0.1 mm substrate

26. 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

27. 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

28. 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

29. 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

30. The Magnetic Hard Disk Drive
Spindle motor
Read-Write Head
Arm
Actuator

31. 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!

32. 1980’s: IBM 3380 Drive The IBM 3380 was the first gigabyte drive
The manufacturing cost was about $ 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

33. 1980’s: IBM 3380 Drive
One Disk
From Drive

34. Q: What’s Inside an Old 4GB Nano?
A 4 GB 1”
“Microdrive”

35. Disk Drive Basics
“1”
“0”

36. Disk Drive Basics - Writing
Track
Head on slider
Suspension
MR Read Sensor
Magnetic flux leaking from the write-head gap records bits in the magnetic medium
Write Head
Shield
Recording Media B

37. Disk Drive Basics - Reading
Track
Head on slider
Suspension
Resistance of MR read sensor changes in response to fields produced by the recorded bits
MR Read Sensor
Write Head
Shield
Recording Media B

38. Magnetic Write Process
Gap is 100 nm but bits are 25 nm.
How can this be??
100 nm
disk
100 nm

39. Scaling
Shrink everything by factor s (including currents and microstructure)
Areal density of data increases by the factor s2
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?

40. Fundamental Innovations
MR/GMR sensors (1991/1997)
AFC media (2001)
to 100 Gb/in2
GMR read
sensor
Perpendicular recording
(2006)
to 500+ Gb/in2
Perpendicular media

41. Longitudinal vs. Perpendicular
Longitudinal recording: horizontal orientation
Perpendicular recording: vertical orientation
(introduced commercially in 2005)

42. Areal Density Increase of Hard Disk Drives*
* CAGR = Cumulative Annual Growth Rate

43. 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

44. 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

45. Future Technology? HAMR-Heat Assisted Magnetic Recording
Patterned Media

46. 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

47. Flash Memories

48. Flash Memory Summit
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49. 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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50. Flash Memory Cell 1 3 2
Introduce errors

51. Cell programming
How we discharge
01

52. Block erasure
Is it a problem?
10

53. Gartner & Phison
What are the coding problems

54. Fast
Low Power
Reliable
Reuse with coding
~104 P/E Cylces

55. 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

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.
q-1- . . 3- 2- 1- 0-
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57. 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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58. 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 ~ 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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59. SLC, MLC and TLC Flash SLC Flash MLC Flash TLC Flash 1 01 00 10 11 011
High Voltage
High Voltage
High Voltage 1 01 00 10 11
011
010
000
001
101
100
110
111
SLC Flash
MLC Flash
TLC Flash
1 Bit Per Cell
2 States
2 Bits Per Cell
4 States
3 Bits Per Cell
8 States
Low Voltage
Low Voltage
Low Voltage
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60. 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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61. Flash Memory Structure
MSB/LSB
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 01 10 00 11
Row index
MSB of first 214 cells
LSB of first 214 cells
MSB of last 214 cells
LSB of last 214 cells
page 0
page 4
page 1
page 5 1
page 2
page 8
page 3
page 9 2
page 6
page 12
page 7
page 13 3
page 10
page 16
page 11
page 17 ⋮ 30
page 118
page 124
page 119
page 125 31
page 122
page 126
page 123
page 127
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62. Flash Memory Structure
MSB Page CSB Page LSB Page MSB Page CSB Page LSB Page
Row index
MSB of first 216 cells
CSB of first 216 cells
LSB of first 216 cells
MSB of last 216 cells
CSB of last 216 cells
LSB of last 216 cells
page 0
page 1 1
page 2
page 6
page 12
page 3
page 7
page 13 2
page 4
page 10
page 18
page 5
page 11
page 19 3
page 8
page 16
page 24
page 9
page 17
page 25 4
page 14
page 22
page 30
page 15
page 23
page 31 ⋮ 62
page 362
page 370
page 378
page 363
page 371
page 379 63
page 368
page 376
page 369
page 377 64
page 374
page 382
page 375
page 383 65
page 380
page 381
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63. Raw BER Results
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64. BER per page for MLC block
MSB/LSB
×10-3 01 10 00 11
Pages, colored the same, behave similarly
×105
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65. Raw BER Results 011 010 000 001 101 100 110 111 High Voltage
Low Voltage
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66. Flash Memory Summit
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