M262 Putting Computers Systems to Work

T325: Technologies for digital media Second semester 2011/2012Tutorial 2 Information Storage1Arab Open University Spring 2012 11OutlineRotating mediaOptical mediaSolid-state memory

Arab Open University Spring 2012 2Rotating MediaArab Open University Spring 2012 3QuestionWhy are we still using CDs and DVDs despite the huge competition of semiconductor memories?Arab Open University Spring 2012 4Semi-conductor vs. Rotating mediaArab Open University Spring 2012 5Disc or Disk ?Both spellings are commonDisk for magnetic media (Hard Disk)Disc for optical media (Blue-ray disc) Arab Open University Spring 2012 6Magnetic disksMagnetic media have a ferromagnetic surface on which areas can be magnetised Some metals, such as iron and its alloys, may be magnetised (permanent magnetism)Information may be encoded as a pattern of magnetismThis pattern can subsequently be detected and the information retrievedNon-volatile medium Patterns persist until the material is demagnetised or re-magnetisedDoes not depend on a continual supply of powerArab Open University Spring 2012 7Magnetic disks

Arab Open University Spring 2012 8Magnetic disksHow read/write operations are performed in a magnetic disk drive?a write head converts electrical signals to magnetised areas on the disk surface, or changes an already magnetised area. a read head produces an electrical signal in response to a magnetic field. The two heads are constructed as a single assembly and mounted on an arm which can move radially across the spinning disk, so that any point on the recording surface may be reached.Data is recorded in concentric tracks, with each track being written or read with the heads at a certain nominal radius

Arab Open University Spring 2012 9Magnetic disksReading and writing operation in Magnetic disks rely on the relation between electricity and magnetism

What is this relation?Arab Open University Spring 2012 10Relationship between electricity and magnetismExperimentsAny electrical conductor carrying a current is associated with it a magnetic fieldA compass needle was deflected by a nearby wire carrying an electric current connection between magnetism and electricity (Hans Christian Oersted (1777-1851))Two current carrying wires attracted or repelled each other (depending on the direction of the currents) due to their magnetic fields (Andr-Marie Ampre (1775-1836))Electric currents could be produced by a magnetic field as long as the field was varying with time (Michael Faraday (1791-1867)) Arab Open University Spring 2012 11Rotating mediaHow can we apply these experiments results on the HDD R/W operations?A write head is an electromagnet constructed so as to concentrate the magnetic field over a very small area of the surface of the disk.If there is sufficient current through the write head, the magnetic field is intense enough to magnetise this area permanently (or until the next write).By varying the current as the disk rotates under the head, a pattern of magnetism is built up along the track, corresponding to a stream of bits.

Arab Open University Spring 2012 12QuestionDoes the converse of the operation work to read out the stored information? Faradays law

Arab Open University Spring 2012 13Rotating mediaAnswer: Yes, but there is a subtle and important difference!Faradays law of magnetic induction: Changing magnetic field DOES generate a current As the disk rotates under the head, the magnetic field it encounters does indeed change frequently, with consecutive areas being magnetised in either of two directions. A head of this type does produce a voltage signalThis signal represents the transitions between magnetic states rather than the states themselves.Arab Open University Spring 2012 14Limitation of the original R/W schemeThe presented R/W scheme is how almost all magnetic recording was done up until the 1990s BUT!Growth of demand for larger data storage capacitiesGreater areal densitySmaller diameter disks Magnetic bits become smaller (radially and along the track)This constitutes a limitation for the original R/W scheme Smaller magnetic bits means smaller voltage signal (difficult to be detected against the background noise)Solution Giant MagnetoResistanceArab Open University Spring 2012 15Magneto-resistanceThe effect of magneto-resistance is a change in the electrical resistance of a conductor when it is placed in a magnetic fieldRelates the voltage across a conductor to the current flowing through it in accordance with Ohms law: V = I x RR can be measured by applying a known voltage to the conductor and measuring the current through itArab Open University Spring 2012 16Magnetoresistance for a read head mechanismHow do you think magnetoresistance can be applied in the HDD read head?Changes in resistance are, in principle, rather easier to detect than the tiny amounts of energy that the magnetic bits of a high density disk can generate by induction. The power used for the measurement now comes from an external voltage/Current source.The voltage and current can be made as large as necessary for accurate resultsLimits: excessive I or V could overheat or damage the head Note: magnetoresistance is also known as Anisotropic Magneto-Resistance (AMR)

Arab Open University Spring 2012 17Giant MagnetoResistance (GMR)Although magnetoresistance was observed by William Thomson (Lord Kelvin) 150 years ago, the change in resistance of below 1% was too small to be practically useful.The real breakthrough came with the discovery of Giant magnetoresistance (GMR), when huge resistance changes (e.g. 50%) were reported.Discovered by Albert Fert in France and Peter Grnberg in Germany, working independently.They jointly received the Nobel Prize in Physics in October 2007 for their discovery.GMR read heads were one of the first products of nanotechnology!Arab Open University Spring 2012 18NanotechnologyWhat is nanotechnology?The term nanotechnology covers a wide variety of ideas and techniques, but its defining characteristic is that it deals with objects with dimensions in the order of a nanometer (10-9 m, or a millionth of a millimeter)Many of the techniques used in nanotechnology were developed for the production of microelectronicsThousands and millions of transistors are built on silicon chips

Arab Open University Spring 2012 19Perpendicular Magnetic Recording (PMR)Purpose: to increase areal densitiesIn conventional recording, or longitudinal magnetic recording, the magnetic bits may be thought of as tiny bar magnets which point along the track. In perpendicular recording, the bar magnets are aligned at right angles to the disk and point in and out of the disk surface.

Arab Open University Spring 2012 20Perpendicular Magnetic Recording (PMR)

Arab Open University Spring 2012 21Longitudinal recordingPerpendicular recordingCoercivityIn Perpendicular recording, much stronger magnetic field is required for writing than in case of longitudinal recordingMaterials used for the recording surface should have a much higher coercivityCoercivity is a measure of how difficult a material is to magnetize or demagnetizeHigh coercivity material difficult to magnetize but also difficult to demagnetizeArab Open University Spring 2012 22Optical MediaArab Open University Spring 2012 23Optical Media - IntroductionData is written on a spiral track as a series of pits of various lengthsTrack pitch: Distance between adjacent tracks

Pits and Lands Arab Open University Spring 2012 24

http://www.sonic.net/~ideas/graphics/mma_cd.gif

Optical Media - IntroductionFour layersA polycarbonate disc layer has the data encoded by using bumps.A shiny layer reflects the laser.A layer of lacquer protects the shiny layer.Artwork is screen printed on the top of the discA laser beam reads the CD and is reflected back to a sensor, which converts it into electronic data Arab Open University Spring 2012 25

EOptical Media Reading DataA laser beam is focused onto the track and reflected back The reflected beam is analyzed to detect the pits. Feedback mechanisms (servomechanisms, or servos for short) involving optics, mechanics and electronics ensure that the beam is kept focused on the track and does not drift away from the track. They compensate effectively for minor warping or eccentricity and for some vibration.The data surface is at the opposite side of a transparent polycarbonate substrate from the laser reader. The laser light penetrates the transparent surface before it reaches a point of focus, so it is spread over a relatively wide area and, therefore, is less affected by minor scratches and dust particles.Arab Open University Spring 2012 26Read Only vs. Rewritable CDsFor read-only CDs, the pits are actual indentations in the data surfaceFor rewritable media they are simply areas of different reflectivity from the land that surrounds them.These discs use a material that can exist in one of two physical states or phases: crystalline (where the molecules are arranged in regular patterns) and amorphous (where there is a lack of order). The phase depends on how the material is heated and cooled, and can be changed from one to the other and back again by heat from the laser. This is called phase-change recording.Arab Open University Spring 2012 2727Blu-rayBlu-ray disc (BD) use blue lasers with a wavelength of 405 nm (shorter than CD and DVD) Shorter wavelength means: laser beam can be focused to a smaller spot on the data surface.pits and track pitch (the spacing between tracks) could be reduced in size, increasing the data capacity achievable. Data in Blu-ray is recorded in a similar way to previous rewritable optical discs, although the details differ. The recording surface uses a phase-change material, and the pits are areas of contrasting reflectivity.

Arab Open University Spring 2012 2828Optical mediaArab Open University Spring 2012 29

Optical media - ComparisonArab Open University Spring 2012 30Thickness of the transparent layerOne important design decision was the thickness of the transparent layer covering the data surface. 1.2 mm thickness in CDs 0.6 mm thickness in DVDsThere are optical advantages to be gained by having a much thinner transparent cover layer. If the disc tilts at all, then a thick layer could deflect and defocus the beam.

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Blu-ray DiscIn the Original CD, the pits were laid in a spiral pattern on a flat surfaceBlu-ray discs have a physical spiral track on which the pits are recorded. This track is a spiral grooveThe preformed groove is there to guide the beam so that it deposits pits in the correct spiral pattern

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32Optical media

Arab Open University Spring 2012 33Blu-ray disc

Arab Open University Spring 2012 34Servomechanism in Optical MediaAny optical disc player uses a servomechanism to stay on track. This is a form of closed-loop control where the position of the beam on the track is constantly monitored.This signal is fed back to the motors that position the beam in such a way as to correct the departure.The alternative, open-loop control, does not use monitoring and feedback, but simply relies on very precise mechanics and favorable operating conditions to keep errors to a minimum.

Arab Open University Spring 2012 35Optical mediaAs the disc rotates, the servomechanism ensures that the laser follows the grooveServomechanism will be moving the laser from side to side to follow the wobble.The rate at which it moves from side to side will be determined by the length of the wobbles (the wobble period the distance between peaks) and the speed of rotation. The length of the wobbles is predefined, so the equipment can determine the speed of rotation from the rate at which the laser is moving from side to side.A feedback loop is used to control the speed of rotation, based on measuring the rate at which the servomechanism is having to move the laser from side to side.

Arab Open University Spring 2012 3636Blue-ray Disc : Conclusion of Important featuresBlu-ray data is held as a pattern of pits along a track.The laser beam reading the data is kept on the track and in focus by a servomechanism.The track also produces a wobble signal. The wobble information is used in locating blocks of data.Small dust particles may corrupt only a few bytes, but marks or scratches might extend for some distance along the track and cause errors in a long sequence of data.When data is recorded it is encoded with an error-correcting code (Reed-Solomon (or RS) code). This allows a large proportion of the errors to be corrected.Arab Open University Spring 2012 3737Solid State MemoryArab Open University Spring 2012 38Introduction Flash memory development : storage capacity and costVariety of usages: memory keys, memory cards, built-in telephone memoryArab Open University Spring 2012 39

ESolid-state memoryFlash memory is an example of memory that is described as solid-state What do you hear by Solid in the term : Solid State Memory ?In science the solid state means solid as distinct from liquid, gas or plasma. Transistor (Solid-state electronics ) vs. thermionic valve (electrons in a vacuum tube)Solid state vs. Rotating Media solid seems in contrast with the moving mechanical parts of the hard drive. Arab Open University Spring 2012 40Memory BasicsOur main interest is in memory which stores digital media files: audio, and still and moving images. Main memory is comprised of integrated circuitsTwo sorts of Main memory: ROM and RAM. ROM stands for Read-Only MemoryROM (and secondary storage media) are non-volatileROM is used for the programs needed on start-up.RAM stands for random-access memory. Random Access: a data word in any location in the whole memory can be accessed just as quickly as a data word in any other location.RAM is volatile: all the programs and associated data stored in it are lost when the power supply to the RAM is switched off.Arab Open University Spring 2012 4141Programmable ROM (PROM)PROM is programmable ROM. Non-programmable ROM has the data put into it when it is manufactured.PROM, by contrast, is manufactured with no data stored in it and can be programmed by the user (the computer manufacturer for example)Special equipment is needed to program PROM, and it cannot be changed once it is programmed (it cannot be erased).Why using the term programming rather than writing ?because it is all done at once up front, rather than writing individual bits or bytes when needed, although for some devices the distinction is not so clear-cut.

Arab Open University Spring 2012 42Erasable PROM (EPROM) Electrically EPROM (EEPROM)EPROM is Erasable PROMErasable PROM can be erased and reprogrammedEPROM is used specifically for a device that can be erased by exposure to ultra-violet light EEPROM is Electrically Erasable PROMEEPROM is erased with an electrical signal rather than needing UV light.

Arab Open University Spring 2012 43EPROM vs. EEPROMEPROMErasing EPROM has to be done to the whole of the device (UV light is shone onto the whole of the chip)EEPROMEEPROM can be erased one bit or one byte at a time. EEPROM is more complex costs more and it is not possible to fit as much memory on a single integrated circuit.

Arab Open University Spring 2012 44QuestionWhat is the meaning of the term flash in Flash Memory ?Arab Open University Spring 2012 45Flash MemoryFlash memory is a variation of EEPROMThe word flash is used in reference to the way it is erased, which is done either on the whole device at once or on a block of data in the device and can be done quickly, in a flash.Offering the electrical erase capability, traditionally featured by the expensive EEPROM, at cost and density comparable to EPROM, Flash memories not only have taken a big portion of their progenitors markets, but in addition they have greatly expanded the fields of application of non-volatile memories. (Source: Bez and Cappelletti, 2005, p. 84)Arab Open University Spring 2012 46Flash Memory CellMemory cell: Part of the memory that can store a single bitCell must be able to exist in each of two states: one state that represents a data 0 one state that represents a data 1Operations: Reading, Erasing, and WritingReading a cell: detecting which of the two states it is in.Erasing a block of memory: setting all the cells in a block to the same known state, that representing a data 1 Writing to the cells (programming the memory): setting some of the cells to the other state, that which represents a data 0.Since the remaining cells are already in the state representing a data 1, there is no need to do anything to themArab Open University Spring 2012 47Solid-state memory

Arab Open University Spring 2012 48Semiconductor TechnologyFlash cells use semiconductor technologyConstructed using the same or similar semiconductor materials and manufacturing processes to those used in microelectronics such as microprocessors.The basic building block of microelectronics is the transistorIn flash memory, a memory cell uses a single transistor. In some other types of semiconductor memory, several transistors are needed for a single memory cell This is one of the reasons that Flash memory allows high storage densitiesArab Open University Spring 2012 49Solid-state memoryArab Open University Spring 2012 50A transistor can be thought of as a controlled switchA signal on the gate connects the source to the drain

Refer to block 1 pages 79 - 83 for more reading about transistorsSolid-state memoryTo read data from a cell, a mechanism is needed to detect whether or not there is charge (electrons) on the floating gateTo read data from a cell, you apply a voltage to the control gate and see whether it succeeds in allowing current to flow between the source and the drain.If it does allow current to flow -- if current is detected at the drain then the data on the cell is a 1; if it does not allow current to flow -- if no current is detected at the drain then the data on the cell is a 0.

Arab Open University Spring 2012 5151Varieties of flashDifferent variations of flash cells is customized for different applicationsDetails of the cell design, Configuration of the cells on the chip, Electronic circuits that accompany the memory cellsIn this course, two categories of flash memory is examinedNAND flash memoryNOR flash memoryThe simplest flash cells only distinguish between two options: charge or no charge (at the floating gate)Multi-level flash is more sophisticated, distinguishing between more than two levels.Arab Open University Spring 2012 52Multi-Level Flash MemoryMulti-level flash: allows more than one bit to be stored in each cell, and hence a higher storage density. For example, suppose in a binary cell a data 1 corresponds to no charge on the gate and a data 0 corresponds to an amount of charge called C.If the system is able to add charge more precisely and also measure how much is on the gate accurately, it might be possible to work with four levels of charge: 0, C/3, 2C/3, C. These four levels could be used to represent two bits of binary data, defined as, for example:0 charge = 11C/3 = 012C/3 = 00C = 10Memory using this system would be described as 2 bits per cell memory.

Arab Open University Spring 2012 5353NAND vs. NOR Flash MemoryNAND flash is optimized for bulk storage, similar to the function of rotating mediaNOR flash is optimized for storage of computer code. The NAND device has a much larger capacity than the NOR device (16 Gbits compared with 1 Gbit).The random access time for the NOR flash is much shorter than for the NAND flash (96 ns compared with 60 ms).NOR can program individual words, whereas NAND needs to program a page at a time.NAND and NOR programming times are similar, being of the order of tens of microseconds.It takes much longer to erase a block in the NOR flash than in the NAND flash (1 s compared with 2.5 ms).The endurance of the NOR flash product is around 10 times that of the NAND flash (100,000 cycles compared to 10,000 cycles).Arab Open University Spring 2012 5454Solid-state memory

Arab Open University Spring 2012 55Solid-state memoryHow does the random access time of this NAND flash compare with that of a HDD that has a latency time of 4.17 ms?Sol:The average random access time (latency) for the HDD was 4.17 ms, which is a lot longer than the 60 micro second for the flash.This is a ratio of

Arab Open University Spring 2012 5656Solid-State memory : Activity 2.9This figure is a simplified display of the memory array configuration (it ignores the use of two planes). Use information from the data sheet in NAND memory Data sheet to find: n, the number of pages per block m, the total number of blocks.From these numbers, calculate (giving separate answers for main memory and spare memory in each case):the total number of bits in a pagethe total number of bits in a blockthe total number of bits in the whole memory. (This should, of course, agree with the total memory size of 16 Gbits of main memory and 512 Mbits of spare memory.)

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Find : n, the number of pages per block; m, the total number of blocks.From these numbers, calculate (giving separate answers for main memory and spare memory in each case):the total number of bits in a pagethe total number of bits in a blockthe total number of bits in the whole memory. Solid-state memoryThe layout of memory cells in NAND flash allows memory cells to be packed more closely together than in NOR flash.According to a paper by Bez and Cappelletti (2005), if the technology node is F, then the space required by a NOR cell is 10F2 and the space required by a NAND cell is 4.5F2.If the technology node F is 65 nm, use these formulas to calculate:The cell size of flash NOR and NAND memory for binary cells (1 bit per cell).The number of bits that can be stored on a chip that is 5mmx5mm.Arab Open University Spring 2012 5959Solid-state memoryF = 65 nm = 65 x10-9 m.NOR cell size is 10F2, which is 10 x(65 x10-9)2m2 = 4.2 x10-14 m2.NAND cell size is 4.5F2, which is 4.5 x(65 10-9)2m2 =1.9 x10-14 m2.5 mm square is (5 x10-3)2m2 = 2.5 x10-5m2.The number of NOR cells that will fit in that area is(2.5 x10-5)/(4.2 x10-14) = 5.9 x108. That is 560 Mbits (with M in the sense of 220 = 1048 576).The number of NAND cells that will fit in that area is (2.5 x10-5)/(1.9 x10-14) = 1.3 x109. That is 1.2 Gbits (with G in the sense of 230 = 1073 741824).Arab Open University Spring 2012 6060Test your knowledge - Questions from previous examsArab Open University - T325 Spring 201261In _________ the magnetic bits may be thought of as tiny bar magnets which point along the tracka. Perpendicular magnetic recordingb. Longitudinal magnetic recordingc. Classic magnetic recordingd. Static magnetic recordinge. None of the above

(Fall 2011 MTA)Arab Open University Spring 2012 62The order of optical media in terms of their capacity from smallest to largest:a. Single Layer Blu-ray disc < Audio CD < Single Layer DVD < Single Layer HD DVD.b. Single Layer DVD < Single Layer HD DVD < Audio CD < Single Layer Bluray disc.c. Single Layer DVD < Audio CD < Single Layer HD DVD < Single Layer Bluray disc.d. Audio CD < Single Layer DVD < Single Layer HD DVD < Single Layer Bluray disc.e. Single Layer DVD < Single Layer Blu-ray disc < Audio CD < Single Layer HD DVD.(Fall 2011 MTA) Arab Open University Spring 2012 63Flash memory is an example of memory that is described as ___________.a. Solid-stateb. Vacuum tubec. Random-accessd. Volatilee. None of the aboveThe change in the electrical resistance of a conductor when it is placed in a magnetic field is called:a. Electro-resistanceb. Magneto-resistancec. Electromagnetic resistanced. Magnetic changee. CoercivityArab Open University Spring 2012 64One of the following is a feature of Blu-raya. Data could not be held as a pattern of pits along a trackb. The track produces a wobble signal which is used in locating blocks of datac. Recorded data is not encoded with an error-correcting coded. It uses solid state structuree. It is volatileArab Open University Spring 2012 65In ___________, the bar magnets are aligned at right angles to the disk and point in and out of the disk surfacea. Conventional magnetic recordingb. Longitudinal magnetic recordingc. Perpendicular magnetic recordingd. Classical magnetic recordinge. None of the aboveWhich of the following is True for a non-volatile mediuma. Patterns persist unless they are removed or changedb. Does not depend on a continual supply of powerc. A typical example of this category is the Read Only Memoryd. All of the above are correcte. None of the above is correctArab Open University Spring 2012 66Briefly explain each of the following items: PROM, EPROM, EEPROM, Multi-Level flash memory, NAND flash memory(Fall 2011 MTA)What are the physical features of Blu-ray and HD-DVD that gives them a higher capacity than CD and DVD?(Fall 2011 Final exam)Explain phase-change recording in Rewritable CDsSummarize the main differences (three at least) between the NAND memory and the NOR memory.Explain in one or two sentences the principle of operation of read and write head in a magnetic disk

Arab Open University Spring 2012 67What are the advantages and disadvantages of EPROM and EEPROM when compared to each other?Rotating media (both optical and magnetic) are in huge competition with semiconductor memories; none of these technologies could dominate and eliminate the other technologies. Explain one reason/advantage that keep each technology in use despite this competition.Arab Open University Spring 2012 68the following information is found in a memory chip data sheet indicating the memory organization : 32768 bits x 128 pages x 4096 blocks x 2 planes. taking into consideration that the organization is presented from the smallest unit size (bit) to the largest unit size (plane). Calculate the followinga. the size of a memory page in KiloBytes (4 marks)b. the size of a memory block in Megabytes (3 marks)c. the size of the memory in Megabytes (3 marks)(Fall 2011 MTA)

Arab Open University Spring 2012 69Consider the following information concerning a multi-level NAND flash memoryThe following levels of charge can be distinguished: 0, C/15, 2C/15... 14C/15, C where C represents the full charge of the transistor.The NAND memory cell size is 2 x10^-14 m^2The memory chip size is 25mm2Answer the following questions:a. How many bits can be represented in each cell?b. How many memory cells the memory chip contains?c. Calculate the storage capacity of the memory chip in GigabytesArab Open University Spring 2012 70