Reading (computer)
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2008-07-07T02:31:25Z
ChyranandChloe
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moved [[Reading (technical)]] to [[Reading (computer)]]: See discussion; better specifies content.
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{{otherusesof|Reading|Reading (disambiguation)}}
'''Reading''' is an action performed by [[computers]], to acquire [[data]] from a source and place it into their [[volatile memory]] for [[processing]]. For example, a computer may read information off a [[floppy disk]] and store it in [[random access memory]] to be placed on the [[hard drive]] to be processed at a future date. Computers may read information from a variety of sources, such as [[magnetic storage]], the [[Internet]], or [[Sound|audio]] and [[video]] input [[Computer port (hardware)|ports]].
The act of reading one unit of information (e.g. a byte) is sometimes called a '''read cycle'''.
The electrical circuit that transforms the physical magnetic flux changes into abstract bits is called the '''read channel'''. A '''read error''' occurs when the physical part of the process fails for some reason, such as dust or dirt entering the drive.
Reading can be abstracted to one of the main functions of a [[Turing machine]].
== History ==
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== Memory types ==
=== CMOS ===
{{main|CMOS}}
Complementary metal–oxide–semiconductor (CMOS) is a [[Non-volatile memory|non-volatile medium]]. It is used in [[microprocessor]]s, [[microcontroller]]s, [[Static Random Access Memory|static RAM]], and other [[digital logic]] circuits. Memory is read through the use of a combination of p-type and n-type [[MOSFET|metal–oxide–semiconductor field-effect transistor]]s (MOSFETs). In CMOS logic, a collection of n-type MOSFETs are arranged in a [[pull-up resistor|pull-down]] [[electrical network|network]] between the output [[node (circuits)|node]] and the lower-voltage [[voltage source|power supply rail]], named [[IC power supply pin|V<sub>ss</sub>]], which often has [[ground (electricity)|ground]] potential. By asserting or de-asserting the inputs to the CMOS circuit, individual transistors along the pull-up and pull-down networks become [[conductive]] and [[Resistivity|resitive]] to eletrical current, and results in the desired path connecting from the output node to one of the voltage rails.{{Fact|date=July 2008}}
=== Flash ===
{{main|Flash memory}}
Flash memory stores information in an array of memory cells made from [[floating-gate transistor]]s. Flash memory is utilizes either NOR logic or NAND logic.
In [[NOR gate]] flash, each cell resembles a standard [[MOSFET]] except the transistor has two gates instead of one. On top is the control gate (CG), as in other MOS transistors, but below this there is a floating gate (FG) insulated all around by an [[oxide]] layer. The FG is interposed between the CG and the [[MOSFET]] channel, and because the FG is electrically isolated by its insulating layer, any [[electron]]s placed on it are trapped there and, under normal conditions, will not discharge for many years. When current flow through the MOSFET channel [[binary code]] is generated, reproducing the stored [[data]].
[[Sheffer stroke#NAND gate|NAND gate]] flash utilizes [[tunnel injection]] for writing and [[tunnel release]] for erasing. NAND flash memory forms the core of the removable [[Universal Serial Bus|USB]] storage devices known as [[USB flash drive]]s, as well as most [[memory card]] formats available today.{{Fact|date=July 2008}}
=== Magnetic ===
{{main|Magnetic storage}}
The magnetic medium is found in magnetic tape, hard disk drives, floppy disks, and so on. This medum uses different patterns of [[magnetization]] in a magnetizable material to store data and is a form of [[non-volatile memory]]. Magnetic storage media can be classified as either [[sequential access memory]] or [[random access memory]] although in some cases the distinction is not perfectly clear.
Small polarized ferrous cores in the shape of wires or poles are flipped along the surface of reading and writing into the desired data is stored. Accessing different parts of the medium involves winding the wire forward or backward until the point of interest is found. Data is read through through a small reading peripheral which amplifies which side the ferrous cores are arranged.{{Fact|date=July 2008}}
=== Mechanical ===
The mechanical medium utilizes one of the oldest methods of computing and has largely become obsolete. The earliest known method of memory storage and subsequent computerized reading is the [[Antikythera mechanism]] (c. 100–150 [[Common Era|BCE]]) which utilizes over thirty gears that spin a dial indicator. Following the Antikythera mechanism, [[Hero of Alexandria]] (c. 10–70 [[Common Era|CE]]) designed a spinning wheel with pegs, when the pegs are reach the wheel in turn reverses the direction of spin. It was used to raise, lower, and moves displays for ampatheatur shows.{{Fact|date=July 2008}}
[[Punch cards]] became popularized from 1900 to 1950 as it became the most common storage medium for computers. The information was read through a method of identifying the holes in the card which was then converted to another medium.{{Fact|date=July 2008}}
=== Peripherals ===
{{Main|Digital signal}}
The usage of electronic computer peripherals became popularized as means of linking two computing devices. Information is sent in electronic singles which are interpreted by a [[Multiplexer]] or multiplexer.{{Fact|date=July 2008}}
=== Optical disks ===
{{main|Optical disc}}
Optical disks refer to the [[non-volatile memory|non-volatile]] flat, circular, usually polycarbonate disks. Data is stored in pits or bumps arranged in sequentially on the continuous, spiral track extending from the innermost track to the outermost track, covering the entire disc surface. Data read by a means of a laser; when the laser enters a pit, the focus of the laser is changed and interpenetrated by the reader's software.
=== RAM ===
{{main|RAM}}
== See also ==
* [[X (writing speed)]]
* [[Computer storage]]
* [[Turing machine]]
* [[Optical character recognition]]
== References ==
=== Notes ===
{{reflist}}
=== Bibliography ===
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== External links ==
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