Reading is an action performed by
computers
A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations (computation) automatically. Modern digital electronic computers can perform generic sets of operations known as programs. These programs ...
, to acquire
data from a source and place it into their
volatile memory for
processing
Processing is a free graphical library and integrated development environment (IDE) built for the electronic arts, new media art, and visual design communities with the purpose of teaching non-programmers the fundamentals of computer programming ...
. Computers may read information from a variety of sources, such as
magnetic storage, the
Internet, or
audio
Audio most commonly refers to sound, as it is transmitted in signal form. It may also refer to:
Sound
*Audio signal, an electrical representation of sound
*Audio frequency, a frequency in the audio spectrum
*Digital audio, representation of sound ...
and
video input
ports. Reading is one of the core functions of a
Turing machine.
A read cycle is the act of reading one unit of information (e.g. a byte). A read channel is an electrical circuit that transforms the physical magnetic flux changes into abstract bits. A read error occurs when the physical part of the process fails for some reason, such as dust or dirt entering the drive.
Example
For example, a computer may read information off a
floppy disk
A floppy disk or floppy diskette (casually referred to as a floppy, or a diskette) is an obsolescent type of disk storage composed of a thin and flexible disk of a magnetic storage medium in a square or nearly square plastic enclosure lined w ...
and store it temporarily in
random-access memory before it is written to the
hard drive to be processed at a future date.
Memory types
CMOS
Complementary metal–oxide–semiconductor (CMOS) is a
non-volatile medium. It is used in
microprocessors,
microcontroller
A microcontroller (MCU for ''microcontroller unit'', often also MC, UC, or μC) is a small computer on a single VLSI integrated circuit (IC) chip. A microcontroller contains one or more CPUs (processor cores) along with memory and programmable i ...
s,
static RAM
Static random-access memory (static RAM or SRAM) is a type of random-access memory (RAM) that uses latching circuitry (flip-flop) to store each bit. SRAM is volatile memory; data is lost when power is removed.
The term ''static'' differen ...
, 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
Ground may refer to:
Geology
* Land, the surface of the Earth not covered by water
* Soil, a mixture of clay, sand and organic matter present on the surface of the Earth
Electricity
* Ground (electricity), the reference point in an electrical c ...
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
resistive to electric 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
The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a type of field-effect transistor (FET), most commonly fabricated by the controlled oxidation of silicon. It has an insulated gate, the voltage of which d ...
, 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
An oxide () is a chemical compound that contains at least one oxygen atom and one other element in its chemical formula. "Oxide" itself is the dianion of oxygen, an O2– (molecular) ion. with oxygen in the oxidation state of −2. Most of the E ...
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
A binary code represents text, computer processor instructions, or any other data using a two-symbol system. The two-symbol system used is often "0" and "1" from the binary number system. The binary code assigns a pattern of binary digits, also ...
is generated, reproducing the stored
data.
NAND gate flash utilizes
tunnel injection
Tunnel injection is a field electron emission effect; specifically a quantum process called Fowler–Nordheim tunneling, whereby charge carriers are injected to an electric conductor through a thin layer of an electric insulator.
It is used to p ...
for writing and
tunnel release
Tunnel injection is a field electron emission effect; specifically a quantum process called Fowler–Nordheim tunneling, whereby charge carriers are injected to an electric conductor through a thin layer of an electric insulator.
It is used to p ...
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 classical electromagnetism, magnetization is the vector field that expresses the density of permanent or induced magnetic dipole moments in a magnetic material. Movement within this field is described by direction and is either Axial or Di ...
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 an entirely mechanical play almost ten minutes in length, powered by a binary-like system of ropes, knots, and simple machines operated by a rotating cylindrical cogwheel.
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
Non-volatile memory (NVM) or non-volatile storage is a type of computer memory that can retain stored information even after power is removed. In contrast, volatile memory needs constant power in order to retain data.
Non-volatile memory typic ...
flat, circular, usually polycarbonate discs. Data is stored in pits or bumps arranged sequentially on the continuous, spiral track extending from the innermost track to the outermost track, covering the entire disc surface. Data is 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.
Random-access memory
Random-access memory (RAM) is a form of computer data storage. A random-access device allows stored data to be accessed directly in any random order. In contrast, other data storage media such as hard disks, CDs, DVDs and magnetic tape, as well as early primary memory types such as drum memory, read and write data only in a predetermined order, consecutively, because of mechanical design limitations. Therefore, the time to access a given data location varies significantly depending on its physical location. Today, random-access memory takes the form of integrated circuits. Strictly speaking, modern types of DRAM are not random access, as data is read in bursts, although the name DRAM / RAM has stuck. However, many types of SRAM, ROM, OTP, and NOR flash are still random access even in a strict sense. RAM is normally associated with volatile types of memory (such as DRAM memory modules), where its stored information is lost if the power is removed. Many other types of non-volatile memory are RAM as well, including most types of ROM and a type of flash memory called NOR-Flash. The first RAM modules to come into the market were created in 1951 and were sold until the late 1960s and early 1970s.
See also
*
X (writing speed)
*
Computer storage
Computer data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers.
The central processing unit (CPU) of a compute ...
*
Turing machine
*
Optical character recognition
References
{{reflist
Computing terminology