Glossary - D

Data

In computer science, data represents anything usable by a computer, and is often an input to or output from a computer program. The program itself is a sequence of instructions that specifies the tasks that the computer must execute. In this sense, data is everything that is not program code. From another point of view, data are considered binary files that are not readable by a human being, unlike a readable text document. The general size of digital data in 2007 was estimated at 281 trillion gigabytes. Computers carry out the flow of instructions they receive. A sequence of instructions to perform tasks is called a computer program.  The computer performs these tasks which consist of binary code and memory that contains data used by the program but is not performed by a processor. The boundary between the program and data is unclear. For example, the interpreter is a program where the input data is a program code that is not expressed in native computer languages. In many cases, the interpreted program is in a human readable form (text file), which can be opened using a text editor like real text.

Data cluster

In computer file systems, a cluster or allocation unit is the unit of disk space allocation for files and directories. Combining several units into a larger allocation unit reduces the overhead communication with the computer storage devices, reduces fragmentation, and increases the speed and efficiency of data transmission. Storage devices can be any block device (hard disk, CD, DVD, flash memory, tape drive, etc.). Nowadays, they do not typically use allocation blocks smaller than 4 KB, which is the same as the usual size of the memory page. Larger allocation units (8, 16, 32 or 64 KB) reduce overhead and the fragmentation of larger files. When storing small files they may be in too large block allocation, contrary to the increase in overhead. This is due to internal fragmentation. Data blocks (sectors), which are one allocation block, need not be exactly next to each other and may even be discontinuous within a track. This should not be confused with fragmentation, as the sectors are still logically contiguous.

Data miner

A data miner's primary function is to gather data about an end user. Some adware applications may employ data mining abilities.

Database

A database (or Data Base) is an ordered set of information (data) housed on a storage medium. Database software tools enable users to access and manipulate the stored data. The predecessor of the database was the card register database that enabled data to be organized according to different criteria as well as the insertion of new items. All operations were carried out directly by humans. The management of card registers was similar to today's database management.

In 1970, E.F. Codd published an article about the first relational database that viewed data as a table. Around 1974, the first versions of SQL were under development. As this technology developed over the next 10years, it brought with it performance-usable systems, which are comparable to network and hierarchical databases. In the 1990s, the first object-oriented database was developed based on object-oriented languages. These databases were expected to displace the relational systems, however, these expectations were not realized and a compromise was developed in the form of object-relational technology.

Database types can be categorized as follows, according to the methods used for storage and linking:

  • hierarchical database
  • network database
  • relational database
  • object database
  • object-relational database

Defragmentation

In the field of computers and computer technology, defragmentation is usually separated parts of binary information entered into a final unit. Fragmentation occurs when the operating system cannot or will not allocate enough contiguous space to store a complete file as a unit, but instead puts parts of it in the gaps between other files. Separated or fragmented data from large files saved on your computer’s hard drive are often stored in many different places in small subsections, and you can use specialized software to combine these into a single coherent section on the disk. The reading of defragmented data is usually faster than fragmented, and modern file systems such as ext3 are already trying to prevent fragmentation as the data is written.

Desktop environment

The desktop environment includes a graphical user interface that typically provides features such as desktop backgrounds, icons and menus. It also facilitates the control of the operating system and the functionality of various inputs such as mouse clicks and keystrokes. The desktop environment has replaced the outmoded console interface. Its modern and intuitive graphical interface helps the user to easily access, configure and modify many important operating system features, and to access and utilize installed software.

Device driver

A driver, or more correctly, a device driver, is software that enables a computer’s operating system to communicate with the hardware. Some drivers are included in the operating system, others are distributed with the hardware (e.g., on CD-ROM).

Naming device drivers was originally done to indicate and distinguish physical device drivers. Today, the term driver or device driver is often used to denote the parts of an operating system that provide other functionality, rather than access to hardware, and therefore they are no longer literally “device” drivers. A typical example of this includes implementing any type of file system.

The driver manages the hardware and also communicates with the rest of the operating system by using a more general interface that provides device abstraction. The main feature of the abstraction is the use of the same or a similar interface for similar devices. For example block device abstraction enables drives to work the same way with a disk, diskette and CD/DVD.

Device Manager

The Device Manager was first introduced in Microsoft® Windows® 95, and is located in the Control Panel of the Microsoft® Windows® operating systems. The Device Manager allows users to view and control the hardware attached to the computer. Typical hardware devices are disk drives, keyboards, monitors, network adapters, game controllers, and imaging devices.  When a hardware device is not working, it appear highlighted in the Device Manager. Double-clicking on a device will display detailed technical information and properties. The list of hardware devices can be sorted by various criteria and the user can enable and disable them as needed.

Digital camera

A digital camera is a camera that records images in digital format. Captured images are instantly visible on the camera’s built-in display and images can be downloaded to a computer for display, manipulation, printing and archiving. Physical copies of digital images can be reproduced on a variety of printers, including high-end machines that simulate traditional film-based photographic reproduction. Aside from basic functionality, many digital cameras offer a number of additional features designed to enhance functionality and/or the processed image data. In addition, some cameras can also record video, audio and notes for collected images.

The first digital camera, the Fuji® DS-1P, appeared in 1988 with 16 MB of internal memory. In 1991, the first digital SLR was introduced—the Kodak® DCS-100. This model featured a 1.3 megapixel sensor and sold for $13,000 USD.

Disk formatting

Disk formatting is a process in which the external media is initialized to be ready for (first) use. Formatting the drive writes the metadata describing the blank media according to the requisites of the selected file system. Therefore, previously stored data usually isn’t completely removed, but information about how to read the original data is lost. Formatting is accomplished in several steps distinguished by two levels, high and low:

  • High Level Formatting is the process in which file system structures are written on the disk in order to prepare the disk to store programs and data.  The general term “formatting” (without specification), usually refers to this activity.
  • Low Level Formatting (LLF) is the basic formatting completed by the hard drive manufacturer during the production process. First, signs are created at the beginning and end of the track, then the beginnings and endings of sectors are marked, test data is recorded, and finally all data on the hard drive is checked by a test program. Older BIOSes usually permitted LLF, but LLF was less than optimal because it erased all data and the new information written to the disk was not located in exactly the same position, which could cause damage to the disc.

 Formatting does not usually affect original stored data, so an appropriate metadata restore can make original data ​​ available again, but often not completely and only with the help of specialized tools. The possibility of restoring the original data is also dependent on whether or not new data has been written on the disk. If new data has been written to the disc, the original data could be overwritten.

Disk sector

A hard disk consists of many "small" parts, called sectors, which are clearly identifiable by number. This method of addressing is an internal matter within the operating system. The operating system also takes care of everything necessary for us to work with the files we use.  The smallest unit of information storage on the hard disk is one sector (usually 512 bytes for magnetic disks and 2048 bytes for optical discs, while newer hard drives use 4096 byte Advanced Format sectors). Each sector has determined its physical location in the media, which can be expressed by three numbers: SIDE, TRACK and SECTOR.

Domain name

A domain name or Internet domain is a unique name identifier for computers or computer networks that are connected to the Internet. A domain name consists of a succession of several parts each separated by dots. The parts are grouped by information type:

  • First-level or top-level domains (TLDs) are national domains (such as .us, .uk, .ru), regional domains (.eu) or domains targeted to the content type (.info, .org, .net and others).
  • Second-level domains are considered to be an address in the form “www.domainaddress.us” in which “us” is an example of TLDs and the domain’s second order is the “domainaddress”. Second-level domains can be  registered (if the name is still available) at one of the registrars.
  • Third-level domains are in the form “www.subdomain.domainaddress.us” or only “subdomain.domain.us”. In this format, the second-level domain is in the subdomain section. There can be fourth- and fifth-level domains, and so on, with virtually no limitation.

The domain names can use only a small part of the ASCII characters: English alphabet characters, numbers and dashes ( the name cannot begin or end with a dash). Names are not case-sensitive (www.example.com describes the same computer as WWW.Example.CoM), and each part of the name can be up to 63 characters long. The length of the whole name can be up to 255 characters. The number of parts is not limited. Theoretically, the name may be  composed of 127 parts of the single letter.

Download

To “download” means to receive data, software, character sets, etc. from a distant to a nearby computer (or a peripheral device) over a network.  The opposite word for download is “upload” which denotes the sending.  The use of the terms, uploading and downloading often imply that the data sent or received is to be stored permanently or “saved”. It is important to note that "downloading" is not the same as "transferring" (i.e., sending/receiving data between two storage devices would be a transfer of data, but receiving data from the Internet would be considered a download of data).

Download Manager

A download manager is software that facilitates the downloading process and enables users to easily manage their downloaded files and folders. Download managers also enable the control and management of uploaded files and folders. A good download manager will provide a range of functions such as the ability to pause and resume downloads, resume broken downloads, speed up the download process by utilizing more slots, scheduled downloads, searching for mirror sites, etc. Download managers can also speed up the downloading process by splitting the download into two or more parallel segments so that all of the available bandwidth could potentially be used, if the targeted server does not block this functionality.

DVD

DVD (Digital Versatile Disc or Digital Video Disc) is a digital optical data carrier format that can include videos with high quality images and sound, as well as other data. During the development of the DVD, a backward compatibility with CDs was emphasized, thus DVDs are very similar to CDs.

 DVD technology was introduced in Japan in 1996, and to the rest of the world a year later. The official standard recordable / rewritable DVD-R (W) was created by the DVD Forum, which was founded in April 1997. Prices on licensing this technology were so high that another group was formed, the  DVD + RW Alliance, which created a standard (DVD + R (W)) with a less expensive license.

 Like CD media, DVD discs are plastic. DVD discs have a diameter of 120 mm and are 1.2 mm thick. Data is stored under the surface in one or two layers of spiral-shaped tracks, similar to CDs. Data is read by a laser light with a wavelength of 660 nm. This wavelength is shorter than the wavelength used in conjunction with CDs, and is one of the reasons for  the higher capacity of DVDs. In addition, the cross-track distance is smaller,  from 1.6 microns for CDs to 0.74 microns for DVDs. There are three types of recordable and rewritable DVD discs: DVD-R/RW, DVD + R / RW, DVD-RAM.


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