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.

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.

Reading can be abstracted to one of the main functions of a Turing machine.

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 V_ss, 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 electric current, and results in the desired path connecting from the output node to one of the voltage rails.

Error

An error (from the Latin error, meaning "wandering") is an action which is inaccurate or incorrect. In some usages, an error is synonymous with a mistake (for instance, a cook who misses a step from a recipe might describe it as either an error or a mistake), though in technical contexts the two are often distinguished. For instance, in statistics "error" refers to the difference between the value which has been computed and the correct value.

Human behavior

One reference differentiates between "error" and "mistake" as follows:

In human behavior the norms or expectations for behavior or its consequences can be derived from the intention of the actor or from the expectations of other individuals or from a social grouping or from social norms. (See deviance.) Gaffes and faux pas can be labels for certain instances of this kind of error. More serious departures from social norms carry labels such as misbehavior and labels from the legal system, such as misdemeanor and crime. Departures from norms connected to religion can have other labels, such as sin.

Plus

Plus may refer to:

Music

Company Names

SCSI

Small Computer System Interface (SCSI, /ˈskʌzi/ SKUZ-ee) is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical and optical interfaces. SCSI is most commonly used for hard disk drives and tape drives, but it can connect a wide range of other devices, including scanners and CD drives, although not all controllers can handle all devices. The SCSI standard defines command sets for specific peripheral device types; the presence of "unknown" as one of these types means that in theory it can be used as an interface to almost any device, but the standard is highly pragmatic and addressed toward commercial requirements.

History

Parallel Interface

SCSI is derived from "SASI", the "Shugart Associates System Interface", developed circa 1978 and publicly disclosed in 1981. A SASI controller provided a bridge between a hard disk drive's low-level interface and a host computer, which needed to read blocks of data. SASI controller boards were typically the size of a hard disk drive and were usually physically mounted to the drive's chassis. SASI, which was used in mini- and early microcomputers, defined the interface as using a 50-pin flat ribbon connector which was adopted as the first-generation SCSI (SCSI-1) connector. SASI is a fully compliant subset of SCSI-1 so that many, if not all, of the then-existing SASI controllers were SCSI-1 compatible.

Hard disk drive

A hard disk drive (HDD), hard disk, hard drive or fixed disk is a data storage device used for storing and retrieving digital information using one or more rigid ("hard") rapidly rotating disks (platters) coated with magnetic material. The platters are paired with magnetic heads arranged on a moving actuator arm, which read and write data to the platter surfaces. Data is accessed in a random-access manner, meaning that individual blocks of data can be stored or retrieved in any order and not only sequentially. HDDs are a type of non-volatile memory, retaining stored data even when powered off.

Introduced by IBM in 1956, HDDs became the dominant secondary storage device for general-purpose computers by the early 1960s. Continuously improved, HDDs have maintained this position into the modern era of servers and personal computers. More than 200 companies have produced HDD units, though most current units are manufactured by Seagate, Toshiba and Western Digital. As of 2015, HDD production (exabytes per year) and areal density are growing, although unit shipments are declining.