Low-Power Double Data Rate Synchronous Dynamic Random Access Memory abbreviated as Low-Power DDR SDRAM or LPDDR SDRAM, is a type of double data rate synchronous dynamic random-access memory that consumes less power and is targeted for mobile computers. It is known as Mobile DDR, abbreviated as mDDR. In contrast with standard SDRAM, used in stationary devices and laptops and is connected over a 64-bit wide memory bus, LPDDR permits 16- or 32-bit wide channels. Not just as with standard SDRAM, each generation of LPDDR has doubled the internal fetch size and external transfer speed; the original low-power DDR is a modified form of DDR SDRAM, with several changes to reduce overall power consumption. Most significant, the supply voltage is reduced from 2.5 to 1.8 V. Additional savings come from temperature-compensated refresh, partial array self refresh, a "deep power down" mode which sacrifices all memory contents. Additionally, chips are smaller. Samsung and Micron are two of the main providers of this technology, used in tablet computing devices such as the iPhone 3GS, original iPad, Samsung Galaxy Tab 7.0 and Motorola Droid X.
A new JEDEC standard JESD209-2E defines a more revised low-power DDR interface. It is not compatible with either DDR1 or DDR2 SDRAM, but can accommodate either: LPDDR2-S2: 2n prefetch memory, LPDDR2-S4: 4n prefetch memory, or LPDDR2-N: Non-volatile memory. Low-power states are similar to basic LPDDR, with some additional partial array refresh options. Timing parameters are specified for LPDDR-200 to LPDDR-1066. Working at 1.2 V, LPDDR2 multiplexes the control and address lines onto a 10-bit double data rate CA bus. The commands are similar to those of normal SDRAM, except for the reassignment of the precharge and burst terminate opcodes: Column address bit C0 is never transferred, is assumed to be zero. Burst transfers thus always begin at addresses. LPDDR2 has an active-low chip select and clock enable CKE signal, which operate like SDRAM. Like SDRAM, the command sent on the cycle that CKE is first dropped selects the power-down state: If the chip is active, it freezes in place. If the command is a NOP, the chip idles.
If the command is a refresh command, the chip enters the self-refresh state. If the command is a burst terminate, the chip enters the deep power-down state; the mode registers have been expanded compared to conventional SDRAM, with an 8-bit address space, the ability to read them back. Although smaller than a serial presence detect EEPROM, enough information is included to eliminate the need for one. S2 devices smaller than 4 Gbit, S4 devices smaller than 1 Gbit have only four banks, they ignore the BA2 signal, do not support per-bank refresh. Non-volatile memory devices do not use the refresh commands, reassign the precharge command to transfer address bits A20 and up; the low-order bits are transferred by a following Activate command. This transfers the selected row from the memory array to one of 4 or 8 row data buffers, where they can be read by a Read command. Unlike DRAM, the bank address bits are not part of the memory address. A row data buffer may be from 32 to 4096 bytes long, depending on the type of memory.
Rows larger than 32 bytes ignore some of the low-order address bits in the Activate command. Rows smaller than 4096 bytes ignore some of the high-order address bits in the Read command. Non-volatile memory does not support the Write command to row data buffers. Rather, a series of control registers in a special address region support Read and Write commands, which can be used to erase and program the memory array. In May 2012, JEDEC published the JESD209-3 Low Power Memory Device Standard. In comparison to LPDDR2, LPDDR3 offers a higher data rate, greater bandwidth and power efficiency, higher memory density. LPDDR3 achieves a data rate of 1600 MT/s and utilizes key new technologies: write-leveling and command/address training, optional on-die termination, low-I/O capacitance. LPDDR3 supports both discrete packaging types; the command encoding is identical to LPDDR2, using a 10-bit double data rate CA bus. However, the standard only specifies 8n-prefetch DRAM, does not include the flash memory commands.
Products using LPDDR3 include the 2013 MacBook Air, iPhone 5S, iPhone 6, Nexus 10, Samsung Galaxy S4 and Microsoft Surface Pro 3. LPDDR3 went mainstream in 2013, running at 800 MHz DDR, offering bandwidth comparable to PC3-12800 notebook memory in 2011. To achieve this bandwidth, the controller must implement dual-channel memory. For example, this is the case for the 5 Octa. Samsung Electronics introduced the first 4 gigabit 20 nm-class LPDDR3 modules capable of transmitting data at up to 2,133 Mbit/s per pin, more than double the performance of the older LPDDR2, only capable of 800 Mbit/s. Various SoCs from various manufacturers natively support 800 MHz LPDDR3 RAM; such include the Snapdragon 600 and 800 from Qualcomm as well as some SoCs from the Exynos and Allwinner series. On 14 March 2012, JEDEC hosted a conference to explore how future mobile device requirements will drive upcoming standards like LPDDR4. On 30 December 2013, Samsung announced that it had developed the first 20 nm-class 8
Apple Inc. is an American multinational technology company headquartered in Cupertino, that designs and sells consumer electronics, computer software, online services. It is considered one of the Big Four of technology along with Amazon and Facebook; the company's hardware products include the iPhone smartphone, the iPad tablet computer, the Mac personal computer, the iPod portable media player, the Apple Watch smartwatch, the Apple TV digital media player, the HomePod smart speaker. Apple's software includes the macOS and iOS operating systems, the iTunes media player, the Safari web browser, the iLife and iWork creativity and productivity suites, as well as professional applications like Final Cut Pro, Logic Pro, Xcode, its online services include the iTunes Store, the iOS App Store, Mac App Store, Apple Music, Apple TV+, iMessage, iCloud. Other services include Apple Store, Genius Bar, AppleCare, Apple Pay, Apple Pay Cash, Apple Card. Apple was founded by Steve Jobs, Steve Wozniak, Ronald Wayne in April 1976 to develop and sell Wozniak's Apple I personal computer, though Wayne sold his share back within 12 days.
It was incorporated as Apple Computer, Inc. in January 1977, sales of its computers, including the Apple II, grew quickly. Within a few years and Wozniak had hired a staff of computer designers and had a production line. Apple went public in 1980 to instant financial success. Over the next few years, Apple shipped new computers featuring innovative graphical user interfaces, such as the original Macintosh in 1984, Apple's marketing advertisements for its products received widespread critical acclaim. However, the high price of its products and limited application library caused problems, as did power struggles between executives. In 1985, Wozniak departed Apple amicably and remained an honorary employee, while Jobs and others resigned to found NeXT; as the market for personal computers expanded and evolved through the 1990s, Apple lost market share to the lower-priced duopoly of Microsoft Windows on Intel PC clones. The board recruited CEO Gil Amelio to what would be a 500-day charge for him to rehabilitate the financially troubled company—reshaping it with layoffs, executive restructuring, product focus.
In 1997, he led Apple to buy NeXT, solving the failed operating system strategy and bringing Jobs back. Jobs pensively regained leadership status, becoming CEO in 2000. Apple swiftly returned to profitability under the revitalizing Think different campaign, as he rebuilt Apple's status by launching the iMac in 1998, opening the retail chain of Apple Stores in 2001, acquiring numerous companies to broaden the software portfolio. In January 2007, Jobs renamed the company Apple Inc. reflecting its shifted focus toward consumer electronics, launched the iPhone to great critical acclaim and financial success. In August 2011, Jobs resigned as CEO due to health complications, Tim Cook became the new CEO. Two months Jobs died, marking the end of an era for the company. Apple is well known for its size and revenues, its worldwide annual revenue totaled $265 billion for the 2018 fiscal year. Apple is the world's largest information technology company by revenue and the world's third-largest mobile phone manufacturer after Samsung and Huawei.
In August 2018, Apple became the first public U. S. company to be valued at over $1 trillion. The company employs 123,000 full-time employees and maintains 504 retail stores in 24 countries as of 2018, it operates the iTunes Store, the world's largest music retailer. As of January 2018, more than 1.3 billion Apple products are in use worldwide. The company has a high level of brand loyalty and is ranked as the world's most valuable brand. However, Apple receives significant criticism regarding the labor practices of its contractors, its environmental practices and unethical business practices, including anti-competitive behavior, as well as the origins of source materials. Apple Computer Company was founded on April 1, 1976, by Steve Jobs, Steve Wozniak, Ronald Wayne; the company's first product is the Apple I, a computer designed and hand-built by Wozniak, first shown to the public at the Homebrew Computer Club. Apple I was sold as a motherboard —a base kit concept which would now not be marketed as a complete personal computer.
The Apple I went on sale in July 1976 and was market-priced at $666.66. Apple Computer, Inc. was incorporated on January 3, 1977, without Wayne, who had left and sold his share of the company back to Jobs and Wozniak for $800 only twelve days after having co-founded Apple. Multimillionaire Mike Markkula provided essential business expertise and funding of $250,000 during the incorporation of Apple. During the first five years of operations revenues grew exponentially, doubling about every four months. Between September 1977 and September 1980, yearly sales grew from $775,000 to $118 million, an average annual growth rate of 533%; the Apple II invented by Wozniak, was introduced on April 16, 1977, at the first West Coast Computer Faire. It differs from its major rivals, the TRS-80 and Commodore PET, because of its character cell-based color graphics and open architecture. While early Apple II models use ordinary cassette tapes as storage devices, they were superseded by the introduction of a 5 1⁄4-inch floppy disk drive and interface called the Disk II.
The Apple II was chosen to be the desktop platform for the first "killer app" of the business world: VisiCalc, a spreadsheet program. VisiCalc created a business market for the Apple II and gave home users an additional reason to buy an Apple II: compatibility with the office. Before VisiCalc, Apple had been a distant third place c
GLONASS, or "Global Navigation Satellite System", is a space-based satellite navigation system operating as part of a radionavigation-satellite service. It provides an alternative to GPS and is the second navigational system in operation with global coverage and of comparable precision. Manufacturers of GPS navigation devices say that adding GLONASS made more satellites available to them, meaning positions can be fixed more and especially in built-up areas where buildings may obscure the view to some GPS satellites. GLONASS supplementation of GPS systems improves positioning in high latitudes. Development of GLONASS began in the Soviet Union in 1976. Beginning on 12 October 1982, numerous rocket launches added satellites to the system, until the completion of the constellation in 1995. After a decline in capacity during the late 1990s, in 2001, under Vladimir Putin's presidency, the restoration of the system was made a top government priority and funding increased substantially. GLONASS is the most expensive program of the Russian Federal Space Agency, consuming a third of its budget in 2010.
By 2010 GLONASS had achieved 100% coverage of Russia's territory and in October 2011 the full orbital constellation of 24 satellites was restored, enabling full global coverage. The GLONASS satellites' designs have undergone several upgrades, with the latest version, GLONASS-K2, scheduled to enter service in 2019. An announcement predicts the deployment of a group of communications and navigational satellites by 2040; the task includes the delivery to the Moon of a series of spacecraft for orbital research and the establishment of a lunar communications and positioning system. GLONASS is a global satellite navigation system, providing real time position and velocity determination for military and civilian users; the satellites are located in middle circular orbit at 19,100 kilometres altitude with a 64.8 degree inclination and a period of 11 hours and 15 minutes. GLONASS's orbit makes it suited for usage in high latitudes, where getting a GPS signal can be problematic; the constellation operates with eight evenly spaced satellites on each.
A operational constellation with global coverage consists of 24 satellites, while 18 satellites are necessary for covering the territory of Russia. To get a position fix the receiver must be in the range of at least four satellites. GLONASS satellites transmit two types of signal: open standard-precision signal L1OF/L2OF, obfuscated high-precision signal L1SF/L2SF; the signals use similar DSSS binary phase-shift keying modulation as in GPS signals. All GLONASS satellites transmit the same code as their standard-precision signal; the center frequency is 1602 MHz + n × 0.5625 MHz, where n is a satellite's frequency channel number. Signals are transmitted in a 38° cone, using right-hand circular polarization, at an EIRP between 25 and 27 dBW. Note that the 24-satellite constellation is accommodated with only 15 channels by using identical frequency channels to support antipodal satellite pairs, as these satellites are never both in view of an earth-based user at the same time; the L2 band signals use the same FDMA as the L1 band signals, but transmit straddling 1246 MHz with the center frequency 1246 MHz + n×0.4375 MHz, where n spans the same range as for L1.
In the original GLONASS design, only obfuscated high-precision signal was broadcast in the L2 band, but starting with GLONASS-M, an additional civil reference signal L2OF is broadcast with an identical standard-precision code to the L1OF signal. The open standard-precision signal is generated with modulo-2 addition of 511 kbit/s pseudo-random ranging code, 50 bit/s navigation message, an auxiliary 100 Hz meander sequence, all generated using a single time/frequency oscillator; the pseudo-random code is generated with a 9-stage shift register operating with a period of 1 ms. The navigational message is modulated at 50 bits per second; the superframe of the open signal is 7500 bits long and consists of 5 frames of 30 seconds, taking 150 seconds to transmit the continuous message. Each frame is 1500 bits long and consists of 15 strings of 100 bits, with 85 bits for data and check-sum bits, 15 bits for time mark. Strings 1-4 provide immediate data for the transmitting satellite, are repeated every frame.
Strings 5-15 provide non-immediate data for each satellite in the constellation, with frames I-IV each describing five satellites, frame V describing remaining four satellites. The ephemerides are updated every 30 minutes using data from the Ground Control segment; the almanac is updated daily. The more accurate high-precision signal is available for authorized users, such as the Russian military, yet unlike the US P code, modulated by an encrypting W code, the GLONASS restricted-use codes are broadcast in the clear using only security through obscurity; the details of the high-precision signal have not been disclosed. The modulation
In telecommunication, Long-Term Evolution is a standard for wireless broadband communication for mobile devices and data terminals, based on the GSM/EDGE and UMTS/HSPA technologies. It increases the capacity and speed using a different radio interface together with core network improvements; the standard is developed by the 3GPP and is specified in its Release 8 document series, with minor enhancements described in Release 9. LTE is the upgrade path for carriers with both GSM/UMTS networks and CDMA2000 networks; the different LTE frequencies and bands used in different countries mean that only multi-band phones are able to use LTE in all countries where it is supported. LTE is marketed as 4G LTE & Advance 4G, but it does not meet the technical criteria of a 4G wireless service, as specified in the 3GPP Release 8 and 9 document series for LTE Advanced. LTE is commonly known as 3.95G. The requirements were set forth by the ITU-R organization in the IMT Advanced specification. However, due to marketing pressures and the significant advancements that WiMAX, Evolved High Speed Packet Access and LTE bring to the original 3G technologies, ITU decided that LTE together with the aforementioned technologies can be called 4G technologies.
The LTE Advanced standard formally satisfies the ITU-R requirements to be considered IMT-Advanced. To differentiate LTE Advanced and WiMAX-Advanced from current 4G technologies, ITU has defined them as "True 4G". LTE stands for Long Term Evolution and is a registered trademark owned by ETSI for the wireless data communications technology and a development of the GSM/UMTS standards. However, other nations and companies do play an active role in the LTE project; the goal of LTE was to increase the capacity and speed of wireless data networks using new DSP techniques and modulations that were developed around the turn of the millennium. A further goal was the redesign and simplification of the network architecture to an IP-based system with reduced transfer latency compared to the 3G architecture; the LTE wireless interface is incompatible with 2G and 3G networks, so that it must be operated on a separate radio spectrum. LTE was first proposed in 2004 by Japan's NTT Docomo, with studies on the standard commenced in 2005.
In May 2007, the LTE/SAE Trial Initiative alliance was founded as a global collaboration between vendors and operators with the goal of verifying and promoting the new standard in order to ensure the global introduction of the technology as as possible. The LTE standard was finalized in December 2008, the first publicly available LTE service was launched by TeliaSonera in Oslo and Stockholm on December 14, 2009, as a data connection with a USB modem; the LTE services were launched by major North American carriers as well, with the Samsung SCH-r900 being the world's first LTE Mobile phone starting on September 21, 2010, Samsung Galaxy Indulge being the world's first LTE smartphone starting on February 10, 2011, both offered by MetroPCS, the HTC ThunderBolt offered by Verizon starting on March 17 being the second LTE smartphone to be sold commercially. In Canada, Rogers Wireless was the first to launch LTE network on July 7, 2011, offering the Sierra Wireless AirCard 313U USB mobile broadband modem, known as the "LTE Rocket stick" followed by mobile devices from both HTC and Samsung.
CDMA operators planned to upgrade to rival standards called UMB and WiMAX, but major CDMA operators have announced instead they intend to migrate to LTE. The next version of LTE is LTE Advanced, standardized in March 2011. Services are expected to commence in 2013. Additional evolution known as LTE Advanced Pro have been approved in year 2015; the LTE specification provides downlink peak rates of 300 Mbit/s, uplink peak rates of 75 Mbit/s and QoS provisions permitting a transfer latency of less than 5 ms in the radio access network. LTE supports multi-cast and broadcast streams. LTE supports scalable carrier bandwidths, from 1.4 MHz to 20 MHz and supports both frequency division duplexing and time-division duplexing. The IP-based network architecture, called the Evolved Packet Core designed to replace the GPRS Core Network, supports seamless handovers for both voice and data to cell towers with older network technology such as GSM, UMTS and CDMA2000; the simpler architecture results in lower operating costs.
In 2004, NTT Docomo of Japan proposes LTE as the international standard. In September 2006, Siemens Networks showed in collaboration with Nomor Research the first live emulation of an LTE network to the media and investors; as live applications two users streaming an HDTV video in the downlink and playing an interactive game in the uplink have been demonstrated. In February 2007, Ericsson demonstrated for the first time in the world LTE with bit rates up to 144 Mbit/s In September 2007, NTT Docomo demonstrated LTE data rates of 200 Mbit/s with power level below 100 mW during the test. In November 2007, Infineon presented the world’s first RF transceiver named SMARTi LTE supporting LTE functionality in a single-chip RF silicon processed in CMOS In early 2008, LTE test equipment began shipping from several vendors and, at the Mobile World Congress 2008 in Barcelona, Ericsson demonstrated the world’s first end-to-end mobile call enabled by LTE on a small handheld device. M
A barometer is a scientific instrument used to measure air pressure. Pressure tendency can forecast short term changes in the weather. Many measurements of air pressure are used within surface weather analysis to help find surface troughs, high pressure systems and frontal boundaries. Barometers and pressure altimeters are the same instrument, but used for different purposes. An altimeter is intended to be used at different levels matching the corresponding atmospheric pressure to the altitude, while a barometer is kept at the same level and measures subtle pressure changes caused by weather; the word barometer is derived from the Ancient Greek: βάρος, lit.'weight', -meter from Ancient Greek: μέτρον. Although Evangelista Torricelli is universally credited with inventing the barometer in 1643, historical documentation suggests Gasparo Berti, an Italian mathematician and astronomer, unintentionally built a water barometer sometime between 1640 and 1643. French scientist and philosopher René Descartes described the design of an experiment to determine atmospheric pressure as early as 1631, but there is no evidence that he built a working barometer at that time.
On July 27, 1630, Giovanni Battista Baliani wrote a letter to Galileo Galilei explaining an experiment he had made in which a siphon, led over a hill about twenty-one meters high, failed to work. Galileo responded with an explanation of the phenomenon: he proposed that it was the power of a vacuum that held the water up, at a certain height the amount of water became too much and the force could not hold any more, like a cord that can support only so much weight; this was a restatement of the theory of horror vacui, which dates to Aristotle, which Galileo restated as resistenza del vacuo. Galileo's ideas reached Rome in December 1638 in his Discorsi. Raffaele Magiotti and Gasparo Berti were excited by these ideas, decided to seek a better way to attempt to produce a vacuum other than with a siphon. Magiotti devised such an experiment, sometime between 1639 and 1641, Berti carried it out. Four accounts of Berti's experiment exist, but a simple model of his experiment consisted of filling with water a long tube that had both ends plugged standing the tube in a basin full of water.
The bottom end of the tube was opened, water, inside of it poured out into the basin. However, only part of the water in the tube flowed out, the level of the water inside the tube stayed at an exact level, which happened to be 10.3 m, the same height Baliani and Galileo had observed, limited by the siphon. What was most important about this experiment was that the lowering water had left a space above it in the tube which had no intermediate contact with air to fill it up; this seemed to suggest the possibility of a vacuum existing in the space above the water. Torricelli, a friend and student of Galileo, interpreted the results of the experiments in a novel way, he proposed that the weight of the atmosphere, not an attracting force of the vacuum, held the water in the tube. In a letter to Michelangelo Ricci in 1644 concerning the experiments, he wrote: Many have said that a vacuum does not exist, others that it does exist in spite of the repugnance of nature and with difficulty. I argued thus: If there can be found a manifest cause from which the resistance can be derived, felt if we try to make a vacuum, it seems to me foolish to try to attribute to vacuum those operations which follow evidently from some other cause.
It was traditionally thought that the air did not have weight: that is, that the kilometers of air above the surface did not exert any weight on the bodies below it. Galileo had accepted the weightlessness of air as a simple truth. Torricelli questioned that assumption, instead proposed that air had weight and that it was the latter which held up the column of water, he thought that the level the water stayed at was reflective of the force of the air's weight pushing on it. In other words, he viewed the barometer as a balance, an instrument for measurement, because he was the first to view it this way, he is traditionally considered the inventor of the barometer; because of rumors circulating in Torricelli's gossipy Italian neighborhood, which included that he was engaged in some form of sorcery or witchcraft, Torricelli realized he had to keep his experiment secret to avoid the risk of being arrested. He needed to use a liquid, heavier than water, from his previous association and suggestions by Galileo, he deduced by using mercury, a shorter tube could be used.
With mercury, about 14 times denser than water, a tube only 80 cm was now needed, not 10.5 m. In 1646, Blaise Pascal along with Pierre Petit, had repeated and perfected Torricelli's experiment after hearing about it from Marin Mersenne, who himself had been shown the experiment by Torricelli toward the end of 1644. Pascal further devised an experiment to test the Aristotelian proposition that it was vapors from the liquid that filled the space in a barometer, his expe
Flash memory is an electronic non-volatile computer storage medium that can be electrically erased and reprogrammed. Toshiba developed flash memory from EEPROM in the early 1980s and introduced it to the market in 1984; the two main types of flash memory are named after the NOR logic gates. The individual flash memory cells exhibit internal characteristics similar to those of the corresponding gates. While EPROMs had to be erased before being rewritten, NAND-type flash memory may be written and read in blocks which are much smaller than the entire device. NOR-type flash allows a single machine word to be written – to an erased location – or read independently; the NAND type is found in memory cards, USB flash drives, solid-state drives, similar products, for general storage and transfer of data. NAND or NOR flash memory is often used to store configuration data in numerous digital products, a task made possible by EEPROM or battery-powered static RAM. One key disadvantage of flash memory is that it can only endure a small number of write cycles in a specific block.
Example applications of both types of flash memory include personal computers, PDAs, digital audio players, digital cameras, mobile phones, video games, scientific instrumentation, industrial robotics, medical electronics. In addition to being non-volatile, flash memory offers fast read access times, although not as fast as static RAM or ROM, its mechanical shock resistance helps explain its popularity over hard disks in portable devices, as does its high durability, ability to withstand high pressure and immersion in water, etc. Although flash memory is technically a type of EEPROM, the term "EEPROM" is used to refer to non-flash EEPROM, erasable in small blocks bytes; because erase cycles are slow, the large block sizes used in flash memory erasing give it a significant speed advantage over non-flash EEPROM when writing large amounts of data. As of 2013, flash memory costs much less than byte-programmable EEPROM and had become the dominant memory type wherever a system required a significant amount of non-volatile solid-state storage.
Flash memory was invented by Fujio Masuoka while working for Toshiba circa 1980. According to Toshiba, the name "flash" was suggested by Masuoka's colleague, Shōji Ariizumi, because the erasure process of the memory contents reminded him of the flash of a camera. Masuoka and colleagues presented the invention at the IEEE 1987 International Electron Devices Meeting held in San Francisco. Intel Corporation introduced the first commercial NOR type flash chip in 1988. NOR-based flash has long erase and write times, but provides full address and data buses, allowing random access to any memory location; this makes it a suitable replacement for older read-only memory chips, which are used to store program code that needs to be updated, such as a computer's BIOS or the firmware of set-top boxes. Its endurance may be from as little as 100 erase cycles for an on-chip flash memory, to a more typical 10,000 or 100,000 erase cycles, up to 1,000,000 erase cycles. NOR-based flash was the basis of early flash-based removable media.
NAND flash has reduced erase and write times, requires less chip area per cell, thus allowing greater storage density and lower cost per bit than NOR flash. However, the I/O interface of NAND flash does not provide a random-access external address bus. Rather, data must be read on a block-wise basis, with typical block sizes of hundreds to thousands of bits; this makes NAND flash unsuitable as a drop-in replacement for program ROM, since most microprocessors and microcontrollers require byte-level random access. In this regard, NAND flash is similar to other secondary data storage devices, such as hard disks and optical media, is thus suitable for use in mass-storage devices, such as memory cards; the first NAND-based removable media format was SmartMedia in 1995, many others have followed, including: MultiMediaCard Secure Digital Memory Stick, xD-Picture Card. A new generation of memory card formats, including RS-MMC, miniSD and microSD, feature small form factors. For example, the microSD card has an area of just over 1.5 cm2, with a thickness of less than 1 mm.
As of August 2017 microSD cards with capacity up to 400 GB are available. Flash memory stores information in an array of memory cells made from floating-gate transistors. In single-level cell devices, each cell stores only one bit of information. Multi-level cell devices, including triple-level cell devices, can store more than one bit per cell; the floating gate may be non-conductive. In flash memory, each memory cell resembles a standard metal-oxide-semiconductor field-effect transistor except that the transistor has two gates instead of one; the cells can be seen as an electrical switch in which current flows between two terminals and is controlled by a floating gate and a control gate. The CG is similar to the gate in other MOS transistors, but below this, there is the FG insulated all around by an oxide layer; the FG is interposed between the MOSFET channel. Because the FG is electrically isolated by its insulating layer, electrons placed on it are trapped; when the FG is charged with electrons, this charge screens the electric field from the CG, inc
Evolution-Data Optimized is a telecommunications standard for the wireless transmission of data through radio signals for broadband Internet access. EV-DO is an evolution of the CDMA2000 standard which supports high data rates and can be deployed alongside a wireless carrier's voice services, it uses advanced multiplexing techniques including code division multiple access as well as time division multiplexing to maximize throughput. It is a part of the CDMA2000 family of standards and has been adopted by many mobile phone service providers around the world those employing CDMA networks, it is used on the Globalstar satellite phone network. EV-DO service has been or will be discontinued in much of Canada in 2015. An EV-DO channel has a bandwidth of 1.25 MHz, the same bandwidth size that IS-95A and IS-2000 use, though the channel structure is different. The back-end network is packet-based, is not constrained by restrictions present on a circuit switched network; the EV-DO feature of CDMA2000 networks provides access to mobile devices with forward link air interface speeds of up to 2.4 Mbit/s with Rel. 0 and up to 3.1 Mbit/s with Rev. A.
The reverse link rate for Rel. 0 can operate up to 153 kbit/s, while Rev. A can operate at up to 1.8 Mbit/s. It was designed to be operated end-to-end as an IP based network, can support any application which can operate on such a network and bit rate constraints. There have been several revisions of the standard, starting with Release 0; this was expanded upon with Revision A to support Quality of Service and higher rates on the forward and reverse link. In late 2006, Revision B was published, whose features include the ability to bundle multiple carriers to achieve higher rates and lower latencies; the upgrade from EV-DO Rev. A to Rev. B involves a software update of the cell site modem, additional equipment for new EV-DO carriers. Existing cdma2000 operators may have to retune some of their existing 1xRTT channels to other frequencies, as Rev. B requires all DO carriers be within 5 MHz; the initial design of EV-DO was developed by Qualcomm in 1999 to meet IMT-2000 requirements for a greater-than-2Mbit/s down link for stationary communications, as opposed to mobile communication.
The standard was called High Data Rate, but was renamed to 1xEV-DO after it was ratified by the International Telecommunication Union under the designation TIA-856. 1xEV-DO stood for "1x Evolution-Data Only", referring to its being a direct evolution of the 1x air interface standard, with its channels carrying only data traffic. The title of the 1xEV-DO standard document is "cdma2000 High Rate Packet Data Air Interface Specification", as cdma2000 is another name for the 1x standard, numerically designated as TIA-2000. Due to possible negative connotations of the word "only", the "DO"-part of the standard's name 1xEV-DO was changed to stand for "Data Optimized", the full name - EV-DO now stands for "Evolution-Data Optimized." The 1x prefix has been dropped by many of the major carriers, is marketed as EV-DO. This provides a more market-friendly emphasis of the technology being data-optimized; the primary characteristic that differentiates an EV-DO channel from a 1xRTT channel is that it is time multiplexed on the forward link.
This means that a single mobile has full use of the forward traffic channel within a particular geographic area during a given slot of time. Using this technique, EV-DO is able to modulate each user’s time slot independently; this allows the service of users in favorable RF conditions with complex modulation techniques while serving users in poor RF conditions with simpler. The forward channel is divided into each being 1.667 ms long. In addition to user traffic, overhead channels are interlaced into the stream, which include the'pilot', which helps the mobile find and identify the channel, the Media Access Channel which tells the mobile devices when their data is scheduled, the'control channel', which contains other information the network needs the mobile devices to know; the modulation to be used to communicate with a given mobile unit is determined by the mobile device itself. It communicates this information back to the serving sector in the form of an integer between 1 and 12 on the "Digital Rate Control" channel.
Alternatively, the mobile can select a "null" rate, indicating that the mobile either cannot decode data at any rate, or that it is attempting to hand off to another serving sector. The DRC values are as follows: Another important aspect of the EV-DO forward link channel is the scheduler; the scheduler most used is called "proportional fair". It's designed to maximize sector throughput while guaranteeing each user a certain minimum level of service; the idea is to schedule mobiles reporting higher DRC indices more with the hope that those reporting worse conditions will improve in time. The system incorporates Incremental Redundancy Hybrid ARQ; each sub-packet of a multi-slot transmission is a turbo-coded replica of the original data bits. This allows mobiles to acknowledge a packet. For example, if a mobile transmits a DRC index of 3 and is scheduled to receive data