welcome to 236601 - coding and algorithms to memories 1

Welcome to 236601 - Coding and Algorithms to Memories 1

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

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 2012 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

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 One Song 28% of One Song 140 Songs 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 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 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 Beethovens 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

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

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 Disk Arm Read-Write Head Actuator Spindle motor 30

But What is This? A 1975 HDD Factory Floor 31

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

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

IBM 3380 34

1980s: IBM 3380 Drive One Disk From Drive 35

Q: Whats Inside an Old 4GB Nano? A 4 GB 1 Microdrive 36

Disk Drive Basics 1 0 37

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 38

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

Magnetic Write Process disk 100 nm Gap is 100 nm but bits are 25 nm. How can this be?? 100 nm 40

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

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

Longitudinal vs. Perpendicular Longitudinal recording: horizontal orientation Perpendicular recording: vertical orientation (introduced commercially in 2005) 43

Areal Density Increase of Hard Disk Drives * * CAGR = Cumulative Annual Growth Rate 44

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 45

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

Future Technology? HAMR-Heat Assisted Magnetic Recording Patterned Media 47

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

Flash Memories 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. 51

Flash Memory Cell 1 0 3 2 52

Cell programming 0101 53

Block erasure 1010 54

Gartner & Phison 55

Fast Low Power Reliable ~10 5 P/E Cylces 56

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

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

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

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

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

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

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

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

Raw BER Results 65

66 BER per page for MLC block 10 5 10 -3 Pages, colored the same, behave similarly 01 10 00 11 MSB/LSB

Raw BER Results 011 010 000 001 101 100 110 111 High Voltage Low Voltage 67

welcome to 236601 - coding and algorithms to memories 1

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