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Reading (computer)

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 audio and video input 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.

Contents


History

Memory types

CMOS

Complementary metal oxide semiconductor (CMOS) is a non-volatile medium. It is used in microprocessors, microcontrollers, static RAM, and other digital logic circuits. Memory is read through the use of a combination of p-type and n-type metal oxide semiconductor field-effect transistors (MOSFETs). In CMOS logic, a collection of n-type MOSFETs are arranged in a pull-down network between the output node and the lower-voltage power supply rail, named Vss, which often has 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 resitive to electrical current, and results in the desired path connecting from the output node to one of the voltage rails.

Flash

Flash memory stores information in an array of memory cells made from floating-gate transistors. Flash memory 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 electrons 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.

NAND gate flash utilizes tunnel injection for writing and tunnel release for erasing. NAND flash memory forms the core of the removable USB storage devices known as USB flash drives, as well as most memory card formats available today.

Magnetic

The magnetic medium is found in magnetic tape, hard disk drives, floppy disks, and so on. This medium 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 a small reading peripheral which amplifies which side the ferrous cores are arranged.

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 BCE) which utilizes over thirty gears that spin a dial indicator. Following the Antikythera mechanism, Hero of Alexandria (c. 10 70 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 amphitheatre shows.

Punched 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.

Peripherals

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.

Optical discs

Optical discs refer to the non-volatile flat, circular, usually polycarbonate discs. 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

See also

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Source: Wikipedia | The above article is available under the GNU FDL. | Edit this article



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