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16.allowing you to specify which data you wish to keep. Theyare less rugged than other forms of removable solid-statestorage, so you should be very careful when handling andstoring them. Because of newer, smaller cards with biggerstorage capacities, such as xD-Picture Cards and SecureDigital cards, Toshiba has now essentially discontinued theproduction of SmartMedia cards, so they're now difficultto find.On the other hand, CompactFlash cards were developed bySandisk in 1994 and were different from SmartMedia cardsin two important ways:• They're thicker.• They utilize a controller chip.CompactFlash cards consists of a small circuit board withflash-memory chips and a dedicated controller chip, allencased in a rugged shell that is thicker than a SmartMediacard. CompactFlash cards are 43 mm wide and 36 mmlong, and come in two thicknesses: Type I cards are 3.3mm thick, and Type II cards are 5.5 mm thick.MLC memory on the other hand, have two bits of datastored per memory cell and four states: erased (11), twothirds (10), one third (01) or programmed (00), which isbasically also a voltage level used to program the MLCmemory (refer to Table 2 and Figure 6). Multi-level cell(MLC) flash memory stores three or more bits in eachcell, with the "multi-level" referring to the multiple levelsof electrical charge used to store multiple bits per cell.By storing more bits per cell, multi-level cell memory willachieve lower manufacturing costs, but they have slowertransfer speeds, higher power consumption and lowercell endurance than single-level cell memory. MLC flashtechnology is used mostly in standard memory cards. Themulti-bit cell, MBC, is a similar technology to the multilevelcell but stores only two bits per cell.ValueState0 Programmed1 ErasedTable 1: SLC levels*** Note - CompactFlash cards support dual voltage andwill operate at either 3.3 volts or 5 volts.The increased thickness of the card allows for greaterstorage capacity than SmartMedia cards. CompactFlashsizes range from 8 MB to as much as 100GB. The onboardcontroller can increase performance, particularly in devicesthat have slow processors. The case and controller chipadd size, weight and complexity to the CompactFlash cardwhen compared to the SmartMedia card.ValueState00 Fully Programmed01 Partially Programmed10 Partially Erased11 Partially ErasedTable 2: MLC levelsHow flash memory worksFlash Memory stores data in individual memory cells, whichare made of floating-gate transistors (refer to Figure 3).Traditionally, one bit of data was stored in each cell, in socalledSingle-level cells (SLC) and two states: erased (1) orprogrammed (0), which is basically a voltage level used toprogram the SLC memory (refers to Table 1 and Figure 5).SLC memory has the advantage of faster transfer speeds,lower power consumption and higher cell endurance.However, as it stores less data per cell, it costs more permegabyte of storage to manufacture. Due to faster transferspeeds, SLC flash technology is used in high-performancememory cards.Figure 5: SLC voltage referenceFigure 6: MLC voltage referenceFigure 3: Architecture of SLC cells consist of a single transistorwith an additional “floating” gate that can storeelectrons
From Figure 5, “0” or “1” is determined by the thresholdvoltage, Vt, of the cell. The threshold voltage can bemanipulated by the amount of charge put on the floatinggate of the flash cell. Placing charge on the floating gatewill increase the threshold voltage of the cell. When thethreshold voltage is high enough, around 4.0V, the cell willbe read as programmed. No charge, or threshold voltage< 4.0V, will cause the cell to be sensed as erased. SLCflash is used in commercial and industrial applications thatrequire high performance and long-term reliability. Someapplications include industrial grade Compact Flash cardsor Solid State Drives (SSDs).As seen in Figure 6, a flash cell’s ability to store charge iswhy MLC technology works. Since the delta between eachlevel has decreased, the sensitivity between each levelincreases. Thus, more rigidly controlled programming isneeded to manipulate a more precise amount of chargestored on the floating gate. In order for a flash cell to beconsidered MLC technology, the cell must exhibit twocharacteristics:flash by using the charge placement technology. Thus,MLC has greater densities. The read speeds between SLCand MLC are comparable. Reading the level of the flash cellcompares the threshold voltage using a voltage comparator.Thus, the architecture change does not affect sensing. Ingeneral, the read speeds of flash are determined by whichcontroller is used.The endurance of SLC flash is 10 times more than MLCflash. The endurance of MLC flash decreases due toenhanced degradation of Si. This is the main reason whySLC flash is considered industrial grade flash and MLC flashis considered consumer grade flash. Higher temperaturescause more leakage in the cells.Combined with the increased sensitivity required todifferentiate between the levels, this leakage will cause thesensors to read the wrong level. As a result, the operatingtemperature of MLC spans only the commercial range.Leakage is not significant in SLC flash and thus, it canoperate in an industrial temperature range.17.1. Precise charge placement2. Precise charge sensingConclusionThus, MLC flash works the same way as SLC flash. Thethreshold voltage, Vt, is used to manipulate the state ofthe flash. Once again, the amount of charge on the floatinggate is what determines the threshold voltage. As seen infigure 6, current MLC technology uses two bits, or fourlevels. However, it can hold more bits. Equation 1 is ageneric equation to determine how many states are neededfor the desired bits.Equation 1 States = 2NN is equal to the number of desired bits per cell. Forexample, for a cell to hold three bits, you need eight statesequal to: 000, 001, 010, 011, 100, 101, 110, and 111.MLC flash is used in consumer applications that do notrequire long term reliability such as consumer grade USBFlash drives, portable media players (PMP), and CompactFlash cards.SLC and MLC comparisonsSLCMLCDensity 16Mbit 32Mbit 64MbitRead Speed 100ns 120ns 150nsBlock Size 64Kbyte 128KbyteEndurance 100,000 cycles 10,000 cyclesOperatingTemperatureIndustrial CommercialTable 3: SLC and MLC comparisonsLet’s compare each characteristic in Table 3. Using thesame wafer size, you can double the density of the MLCTable 4 summarises the advantages and disadvantages ofSLC flash and MLC flash. •High DensityLow Cost per BitEnduranceOperatingTemperatureRangeLow PowerConsumptionWrite / EraseSpeedsWrite / EraseEnduranceTable 4: Qualities of SLC and MLCReferencesSLCMLC[1] http://en.wikipedia.org/wiki/Single-level_cell[2] http://www.supertalent.com/datasheets/SLC_vs_MLC%20whitepaper.pdf[3] http://forums.anandtech.com[4] http://www.flashbay.com/slc_mlc_usb_flash_drives.htmle-Security | <strong>CyberSecurity</strong> <strong>Malaysia</strong> | Volume 21 - (Q4/2009)
Page 1: Volume 21 - (Q4/2009)“Companies s
Page 4 and 5: 4.MyCERT 4th Quarter 2009 SummaryRe
Page 6 and 7: 6.USB PortA culprit to ICT Security
Page 8 and 9: 8.Specific device setup classes can
Page 10 and 11: 10.ConclusionReferencesUSB removabl
Page 12 and 13: 12.Figure 9: Interpreting “Active
Page 14 and 15: 14.7. A list of time zone propertie
Page 18: 18.Guide to Motion Compensation (Ph
Page 21 and 22: Graph 1 shows all the satisfied poi
Page 23 and 24: CyberdatingHow to Have Funbut Stay
Page 25 and 26: find them. If anything goes wrong,
Page 27 and 28: 27.What could be the threats to ena
Page 29 and 30: 29.InternetRadio Frequency Identifi
Page 31 and 32: Common Criteria andNational Cyber S
Page 33 and 34: 33.Case Study: US Government Direct
Page 35 and 36: has caused a US$2.25 million fine t
Page 37 and 38: 37.lewat sampai pada penerima ataup
Page 39 and 40: For instance TM, Malaysia’s large

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