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ACS |
Attitude Control System. This is the spacecraft subsystem which is responsible for pointing the spacecraft in the desired direction and knowing where the spacecraft is pointed at all times.
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ADC |
Analog to Digital Converter |
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ADDRESS |
- (1) A location of data, usually in main memory or on a disk. You can think of computer memory as an array of storage boxes, each of which is one byte in length. Each box has an address (a unique number) assigned to it. By specifying a memory address, programmers can access a particular byte of data. Disks are divided into tracks and sectors, each of which has a unique address. Usually, you do not need to worry about addresses unless you are a programmer.
- (2) A name or token that identifies a network component. In local area networks (LANs), for example, every node has a unique address. On the Internet, every file has a unique address called a URL.
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ADSL |
Asymmetric Digital Subscriber Line, a new technology that allows more data to be sent over existing copper telephone lines (POTS). ADSL supports data rates of from 1.5 to 9 Mbps when receiving data (known as the downstream rate) and from 16 to 640 Kbps when sending data (known as the upstream rate). ADSL requires a special ADSL modem. ADSL is growing in popularity as more areas around the world gain access. ADSL has distance constraints from Central Office.
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AGP |
Accelerated Graphics Port, a new interface specification developed by Intel Corporation. AGP is based on PCI, but is designed especially for the throughput demands of 3-D graphics. Rather than using the PCI bus for graphics data, AGP introduces a dedicated point-to-point channel so that the graphics controller can directly access main memory. The AGP channel is 32 bits wide and runs at 66 MHz. This translates into a total bandwidth of 266 MBps, as opposed to the PCI bandwidth of 133 MBps. AGP also supports two optional faster modes, with throughputs of 533 MBps and 1.07 GBps. In addition, AGP allows 3-D textures to be stored in main memory rather than video memory.
AGP has a couple important system requirements:
- The chipset must support AGP.
- The motherboard must be equipped with an AGP bus slot or must have an integrated AGP graphics system.
- The operating system must be the OSR 2.1 version of Windows 95, Windows 98 or Windows NT 4.0. And currently, many professional Macintoshes support AGP.
AGP-enabled computers and graphics accelerators hit the market in August, 1997.
However, there are several different levels of AGP compliance. The following features are considered optional:
- Texturing: Also called Direct Memory Execute mode, allows textures to be stored in main memory.
- Throughput: Various levels of throughput are offered: 1X is 266 MBps, 2X is 533 MBps; and 4X provides 1.07 GBps.
- Sideband Addressing: Speeds up data transfers by sending command instructions in a separate, parallel channel.
- Pipelining: Enables the graphics card to send several instructions together instead of sending one at a time.
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AM |
Electronics. Amplitude modulation, the deliberate variation of the amplitude of a radio wave or carrier in order to transmit a signal. Telecommunications. 1. A system of communication or broadcasting that uses amplitude modulation. 2. Using such a system: an AM radio. |
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ANALOG |
Almost everything in the world can be described or represented in one of two forms: analog or digital. The principal feature of analog representations is that they are continuous. In contrast, digital representations consist of values measured at discrete intervals. Digital watches are called digital because they go from one value to the next without displaying all intermediate values. Consequently, they can display only a finite number of times of the day. In contrast, watches with hands are analog, because the hands move continuously around the clock face. As the minute hand goes around, it not only touches the numbers 1 through 12, but also the infinite number of points in between. Early attempts at building computers used analog techniques, but accuracy and reliability were not good enough. Today, almost all computers are digital. |
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ANTENNA |
A device that radiates or receives electromagnetic radiation in the radio frequency or microwave range.
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ANTIVIRUS PROGRAM |
A utility that searches a hard disk for viruses and removes any known viruses that are found. Most antivirus programs include an auto-update feature that enables the program to download profiles of new viruses so that it can check for the new viruses as soon as they are discovered. see also Norton Antivirus
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APPLICATION |
A program or group of programs designed for end users. Software can be divided into two general classes: systems software and applications software. Systems software consists of low-level programs that interact with the computer at a very basic level. This includes operating systems, compilers, and utilities for managing computer resources. In contrast, applications software (also called end-user programs) includes database programs, word processors, and spreadsheets. Figuratively speaking, applications software sits on top of systems software because it is unable to run without the operating system and system utilities. Also called APP.
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ARPANET |
The precursor to the Internet, ARPANET was a large wide-area network created by the United States Defense Advanced Research Project Agency (ARPA). Established in 1969, ARPANET served as a test bed for new networking technologies, linking many universities and research centers. The first two nodes that formed the ARPANET were UCLA and the Stanford Research Institute, followed shortly thereafter by the University of Utah. |
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ASCII |
American Standard Code for Information Interchange. Pronounced ask-ee, ASCII is a code for representing English characters as numbers, with each letter assigned a number from 0 to 127. For example, the ASCII code for uppercase M is 77. Most computers use ASCII codes to represent text, which makes it possible to transfer data from one computer to another. Text files stored in ASCII format are sometimes called ASCII files. Text editors and word processors are usually capable of storing data in ASCII format, although ASCII format is not always the default storage format. Most data files, particularly if they contain numeric data, are not stored in ASCII format. Executable programs are never stored in ASCII format. The standard ASCII character set uses just 7 bits for each character. There are several larger character sets that use 8 bits, which gives them 128 additional characters. The extra characters are used to represent non-English characters, graphics symbols, and mathematical symbols. Several companies and organizations have proposed extensions for these 128 characters. The DOS operating system uses a superset of ASCII called extended ASCII or high ASCII. A more universal standard is the ISO Latin 1 set of characters, which is used by many operating systems, as well as Web browsers. |
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AS_AGENT |
AS_AGENT, officially called RPA Remote Page Accelerator is used to speed up your browsing experience on a Starband unit, by prefetching information at the Network Operations Center and streaming it back to you. For more information and a graphical overview please see click here. |
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ATM |
Asynchronous Transfer Mode, a network technology based on transferring data in cells or packets of a fixed size. The cell used with ATM is relatively small compared to units used with older technologies. The small, constant cell size allows ATM equipment to transmit video, audio, and computer data over the same network, and assure that no single type of data hogs the line. Current implementations of ATM support data transfer rates of from 25 to 622 Mbps (megabits per second). This compares to a maximum of 100 Mbps for Ethernet, the current technology used for most LANs. Some people think that ATM holds the answer to the Internet bandwidth problem, but others are skeptical. ATM creates a fixed channel, or route, between two points whenever data transfer begins. This differs from TCP/IP, in which messages are divided into packets and each packet can take a different route from source to destination.
This difference makes it easier to track and bill data usage across an ATM network, but it makes it less adaptable to sudden surges in network traffic.
When purchasing ATM service, you generally have a choice of four different types of service:
- Constant Bit Rate (CBR) specifies a fixed bit rate so that data is sent in a steady stream. This is analogous to a leased line.
- Variable Bit Rate (VBR) provides a specified throughput capacity but data is not sent evenly. This is a popular choice for voice and videoconferencing data.
- Unspecified Bit Rate (UBR) does not guarantee any throughput levels. This is used for applications, such as file transfer, that can tolerate delays.
- Available Bit Rate (ABR) provides a guaranteed minimum capacity but allows data to be bursted at higher capacities when the network is free.
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ATTACHMENT |
A file attached to an e-mail message. Many e-mail systems only support sending text files as e-mail. If the attachment is a binary file or formatted text file (such as an MS-Word document), it must be encoded before it is sent and decoded once it is received. There are a number of encoding schemes, the two most prevalent being Uuencode and MIME.
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ATTRIBUTE |
- (1) A characteristic. In a word processing application, an underlined word would be said to have the underline attribute. In database systems, a field can have various attributes. For example, if it contains numeric data, it has the numeric attribute.
- (2) In database management systems, the term attribute is sometimes used as a synonym for field.
- (3) In DOS systems, every file has a file attributes that indicate several properties of the file. For example, they indicate whether the file is read-only, whether it needs to be backed up, and whether it is visible or hidden.
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AUTUMNAL EQUINOX |
The moment when the sun crosses the celestial equator from north to south; this occurs approximately on September 23rd. see EQUINOX and VERNAL EQUINOX.
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AZIMUTH |
The point on the horizon to which you are going to aim the antenna. In the case of antenna installation, set your azimuth for South.
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BANDWIDTH |
The amount of data that can be transmitted in a fixed amount of time. For digital devices, the bandwidth is usually expressed in bits per second (bps) or bytes per second. For analog devices, the bandwidth is expressed in cycles per second, or Hertz (Hz). The bandwidth is particularly important for I/O devices. For example, a bus with a low bandwidth can hamper a fast disk drive. This is the main reason that new buses, such as AGP, have been developed for the PC. |
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BASIC |
Beginners All-Purpose Symbolic Instruction Code. Computer programming language. |
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BAUD |
Telecommunications. In telegraphy, a unit of signaling speed, equal to the number of pulses and spaces that are transmitted per second. If the pulses have only one level, then the bits per second is equivalent to bauds; if the pulses are multilevel, then the rate in bauds contains additional information, and the number of bits per second is a greater number. Computer Science. In a computer system, the number of signal elements, usually bits, that can be transmitted per second. Also, baud rate. (Named for Émile Baudot.) |
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BBS |
An electronic message center. Most bulletin boards serve specific interest groups. They allow you to dial in with a modem; review messages left by others, and leave your own message if you want. Bulletin boards are a particularly good place to find free or inexpensive software products. In the United States alone, there are tens of thousands of BBSs.
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BEACON |
Low-power carrier transmitted by a satellite, which supplies the controlling engineers on the ground with a means of monitoring telemetry data, tracking the satellite, or conducting propagation experiments. This tracking beacon usually uses a horn or omni antenna. |
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BER |
Bit Error Rate. A value given to signal integrity. The lower the BER the less loss or errors that requires information to be resent. Lower BER indicates better signal. |
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BIOS |
Basic Input/Output System. The BIOS is built-in software that determines what a computer can do without accessing programs from a disk. On PCs, the BIOS contains all the code required to control the keyboard, display screen, disk drives, serial communications, and a number of miscellaneous functions. The BIOS is typically placed in a ROM chip that comes with the computer (it is often called a ROM BIOS). This ensures that the BIOS will always be available and will not be damaged by disk failures. It also makes it possible for a computer to boot itself. Because RAM is faster than ROM, though, many computer manufacturers design systems so that the BIOS is copied from ROM to RAM each time the computer is booted. This is known as shadowing. Many modern PCs have a flash BIOS, which means that the BIOS has been recorded on a flash memory chip, which can be updated if necessary. The PC BIOS is fairly standardized; so all PCs are similar at this level (although there are different BIOS versions). Additional DOS functions are usually added through software modules. This means you can upgrade to a newer version of DOS without changing the BIOS. PC BIOSes that can handle Plug-and-Play (PnP) devices are known as PnP BIOSes, or PnP-aware BIOSes. These BIOSes are always implemented with flash memory rather than ROM. |
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BIT |
Short for BInary digiT, the smallest unit of information on a machine. The term was first used in 1946 by John Tukey, a leading statistician and adviser to five presidents. A single bit can hold only one of two values: 0 or 1. More meaningful information is obtained by combining consecutive bits into larger units. For example, a byte is composed of 8 consecutive bits. Computers are sometimes classified by the number of bits they can process at one time or by the number of bits they use to represent addresses. These two values are not always the same, which leads to confusion. For example, classifying a computer as a 32-bit machine might mean that its data registers are 32 bits wide or that it uses 32 bits to identify each address in memory. Whereas larger registers make a computer faster, using more bits for addresses enables a machine to support larger programs. Graphics are also often described by the number of bits used to represent each dot. A 1-bit image is monochrome; an 8-bit image supports 256 colors or grayscales; and a 24- or 32-bit graphic supports true color. |
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BMP |
The standard Bit-MaPped graphics format used in the Windows environment. By convention, graphics files in the BMP format end with a .BMP extension. BMP files store graphics in a format called device-independent bitmap (DIB).
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BOOT |
To load the first piece of software that starts a computer. Because the operating system is essential for running all other programs, it is usually the first piece of software loaded during the boot process.
Boot is short for bootstrap, which in olden days was a strap attached to the top of your boot that you could pull to help get your boot on. Hence, the expression, "pull oneself up by the bootstraps." Similarly, bootstrap utilities help the computer get started. A cold boot is when you turn the computer on from an off position. A warm boot is when you reset a computer that is already on.
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BPI |
Bytes Per Inch. Unit of measurement developed by DirecPC.
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BPS |
Bits Per Second, the standard measure of data transmission speeds.
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BROADBAND |
A type of data transmission in which a single medium (wire) can carry several channels at once. Cable TV, for example, uses broadband transmission. In contrast, baseband transmission allows only one signal at a time. Most communications between computers, including the majority of local-area networks, use baseband communications. An exception is B-ISDN networks, which employ broadband transmission.
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BROWSER |
Web browser, a software application used to locate and display Web pages. The two most popular browsers are Netscape Navigator and Microsoft's Internet Explorer. Both of these are graphical browsers, which means that they can display graphics as well as text. In addition, most modern browsers can present multimedia information, including sound and video, though they require plug-ins for some formats.
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BUD |
Big Ugly Dish From the early TVRO days when a C-band dish was 8 to 10 feet in diameter. |
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BUFFER |
Temporary storage used to accommodate differences in speed of data flow when transmitting from one device to another.
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BUS |
- (1) A collection of wires through which data is transmitted from one part of a computer to another. You can think of a bus as a highway on which data travels within a computer. When used in reference to personal computers, the term bus usually refers to internal bus. This is a bus that connects all the internal computer components to the CPU and main memory. There's also an expansion bus that enables expansion boards to access the CPU and memory. All buses consist of two parts -- an address bus and a data bus. The data bus transfers actual data whereas the address bus transfers information about where the data should go. The size of a bus, known as its width, is important because it determines how much data can be transmitted at one time. For example, a 16-bit bus can transmit 16 bits of data, whereas a 32-bit bus can transmit 32 bits of data.Every bus has a clock speed measured in MHz. A fast bus allows data to be transferred faster, which makes applications run faster. On PCs, the old ISA bus is being replaced by faster buses such as PCI. Nearly all PCs made today include a local bus for data that requires especially fast transfer speeds, such as video data. The local bus is a high-speed pathway that connects directly to the processor. Several different types of buses are used on Apple Macintosh computers. Older Macs use a bus called NuBus, but newer ones use PCI.
- (2) In networking, a bus is a central cable that connects all devices on a local-area network (LAN). It is also called the backbone.
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BYTE |
Abbreviation for binary term, a unit of storage capable of holding a single character. On almost all modern computers, a byte is equal to 8 bits. Large amounts of memory are indicated in terms of kilobytes (1,024 bytes), megabytes (1,048,576 bytes), and gigabytes (1,073,741,824 bytes). A disk that can hold 1.44 megabytes, for example, is capable of storing approximately 1.4 million characters, or about 3,000 pages of information.
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C-BAND |
Electromagnetic signals in the 4 to 6 GHz range. These signals are susceptible to terrestrial microwave interference. This format required the use of a 8' to 10' antenna due to the satellite transponders only using 4-16 watt transmitters.
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Carrier
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Noise Ratio |
Both co-pol and cross-pol signals consist of (1) the CW test carrier transmitted by the VSAT, and (2) background noise. C/N is the difference between these two quantities as seen on the spectrum analyzer display.
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CAT-5 |
Category 5 describes network cabling that consists of four twisted pairs of copper wire terminated by RJ45 connectors. Cat-5 cabling supports frequencies up to 100 MHz and speeds up to 100 Mbps. It can be used for ATM, token ring, 1000Base-T, 100Base-T, and 10Base-T networking. Computers hooked up to LAN s are connected using Cat-5 cables, so if you're on a LAN, most likely the cable running out of the back of your PC is Category 5. Cat-5 is based on the EIA/TIA 568 Commercial Building Telecommunications Wiring Standard developed by the Electronics Industries Association as requested by the Computer Communications Industry Association in 1985. |
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CCC |
StarBand Customer Care Center. |
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CD |
CD, a compact disc is a polycarbonate with one or more metal layers capable of storing digital information. The most prevalent types of compact discs are those used by the music industry to store digital recordings and CD-ROMs used to store computer data. Both of these types of compact disc are read-only, which means that once the data has been recorded onto them, they can only be read, or played. Another type of compact disc, called CD-Rs and CD_RWs, can have their data erased and overwritten by new data. Currently, erasable optical storage is too slow to be used as a computer's main storage facility, but as the speed improves and the cost comes down, optical storage devices are becoming a popular alternative to tape systems as a backup method. |
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CDMA |
Code Division Multiple Access. A multiple access scheme for digital communications which uses spread spectrum modulation and orthogonal codes to avoid interference and permit many users to occupy all of the transponder bandwidth all of the time.
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CDROM |
Compact Disc-Read-Only Memory. A type of optical disk capable of storing large amounts of data -- up to 1GB, although the most common size is 650MB (megabytes). A single CD-ROM has the storage capacity of 700 floppy disks, enough memory to store about 300,000 texts. CD-ROMs are stamped by the vendor, and once stamped, they cannot be erased and filled with new data. To read a CD, you need a CD-ROM player. All CD-ROMs conform to a standard size and format, so you can load any type of CD-ROM into any CD-ROM player. In addition, CD-ROM players are capable of playing audio CDs, which share the same technology. CD-ROMs are particularly well suited to information that requires large storage capacity. This includes color large software applications, graphics, sound, and especially video. |
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CENTRAL OFFICE |
Telecommunications. CO. A telephone-switching office at which a common carrier terminates and interconnects user lines with other user lines or trunk circuits to connecting offices or other switching systems.
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CERTIFICATION NUMBER |
Unique number given to an installer who has been certified to do Starband installs. A separate certification number is needed for the Skyblaster and Models 180 and 360.
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CGI |
Common Gateway Interface, a specification for transferring information between a World Wide Web server and a CGI program. A CGI program is any program designed to accept and return data that conforms to the CGI specification. The program could be written in any programming language, including C, Perl, Java, or Visual Basic. CGI programs are the most common way for Web servers to interact dynamically with users. Many HTML pages that contain forms, for example, use a CGI program to process the form's data once it's submitted. Another increasingly common way to provide dynamic feedback for Web users is to include scripts or programs that run on the user's machine rather than the Web server. These programs can be Java applets, Java scripts, or ActiveX controls. These technologies are known collectively as client-side solutions, while the use of CGI is a server-side solution because the processing occurs on the Web server. One problem with CGI is that each time a CGI script is executed, a new process is started. For busy Web sites, this can slow down the server noticeably. A more efficient solution, but one that it is also more difficult to implement, is to use the server's API, such as ISAPI or NSAPI. Another increasingly popular solution is to use Java servlets. |
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CHAP |
Short for Challenge Handshake Authentication Protocol, a type of authentication in which the authentication agent (typically a network server) sends the client program a key to be used to encrypt the username and password. This enables the username and password to be transmitted in an encrypted form to protect them against eavesdroppers. Contrast with PAP. |
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CHIP |
A small piece of semiconducting material (usually silicon) on which an integrated circuit is embedded. A typical chip is less than 1/4-square inches and can contain millions of electronic components (transistors). Computers consist of many chips placed on electronic boards called printed circuit boards. There are different types of chips. For example, CPU chips (also called microprocessors) contain an entire processing unit, whereas memory chips contain blank memory. Chips come in a variety of packages. The three most common are:
- DIPs: Dual in-line packages are the traditional bug like chips that have anywhere from 8 to 40 legs, evenly divided in two rows.
- PGAs: Pin-grid arrays are square chips in which the pins are arranged in concentric squares.
- SIPs: Single in-line packages are chips that have just one row of legs in a straight line like a comb.
In addition to these types of chips, there are also single in-line memory modules (SIMMs), which consist of up to nine chips packaged as a single unit. |
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CLARKE BELT |
Named for writer Arthur C. Clarke, who first suggested using satellites for relaying communications, the Clarke Belt is approximately 23,000 miles above the equator and is the orbit for communications satellites.
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CLIENT |
The client part of a client-server architecture. Typically, a client is an application that runs on a personal computer or workstation and relies on a server to perform some operations. For example, an e-mail client is an application that enables you to send and receive e-mail. |
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CLOCK SPEED |
Also called clock rate, the speed at which a microprocessor executes instructions. Every computer contains an internal clock that regulates the rate at which instructions are executed and synchronizes all the various computer components. The CPU requires a fixed number of clock ticks (or clock cycles) to execute each instruction. The faster the clock, the more instructions the CPU can execute per second. Clock speeds are expressed in megahertz (MHz), 1 MHz being equal to 1 million cycles per second. The CPUs of Personal computers have clock speeds of anywhere from 33 MHz to over 300 MHz. The internal architecture of a CPU has as much to do with a CPU's performance as the clock speed, so two CPUs with the same clock speed will not necessarily perform equally. Whereas an Intel 80286 microprocessor requires 20 cycles to multiply two numbers, an Intel 80486 or later processor can perform the same calculation in a single clock tick. (Note that clock tick here refers to the system's clock, which runs at 66 MHz for all PCs.) These newer processors, therefore, would be 20 times faster than the older processors even if their clock speeds were the same. In addition, some microprocessors are superscalar, which means that they can execute more than one instruction per clock cycle. Like CPUs, expansion buses also have clock speeds. Ideally, the CPU clock speed and the bus clock speed should be the same so that neither component slows down the other. In practice, the bus clock speed is often slower than the CPU clock speed, which creates a bottleneck. This is why new local buses, such as AGP, have been developed.
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CMOS |
Complimentary Metal Oxide Semiconductor Pronounced see-moss, CMOS is a widely used type of semiconductor. CMOS semiconductors use both NMOS (negative polarity) and PMOS (positive polarity) circuits. Since only one of the circuit types is on at any given time, CMOS chips require less power than chips using just one type of transistor. This makes them particularly attractive for use in battery-powered devices, such as portable computers. Personal computers also contain a small amount of battery-powered CMOS memory to hold the date, time, and system setup parameters.
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CNR |
Communication and Networking Riser. Developed by Intel, CNR is a riser card for ATX family motherboards that was developed in order to reduce the cost to OEMs of implementing LAN, home networking, audio and modem subsystems widely used in modern connected PCs. The CNR Specification is an open industry specification that defines a scalable motherboard riser card and interface that support the audio, modem, and network interfaces of core logic chipsets. The specification is supported by OEMs, Microsoft Corporation and silicon suppliers. The specification defines the CNR architecture for both standard and low-profile risers and includes electrical, mechanical, and thermal requirements of the riser interface. In addition to supporting current technologies such as Ethernet and analog modems, the specification can be expanded for developing technologies, such as DSL. |
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CO-POL |
The signal that provides an indication of the quality of the CW test signal present in the polarization assigned for normal operation. This signal is maximized to provide the best VSAT performance.
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CODE |
- (n) (1) A set of symbols for representing something. For example, most computers use ASCII codes to represent characters.
- (2) Written computer instructions. The term code is somewhat colloquial. For example, a programmer might say: "I wrote a lot of code this morning" or "There's one piece of code that doesn't work."
Code can appear in a variety of forms. The code that a programmer writes is called source code. After it has been compiled, it is called object code. Code that is ready to run is called executable code or machine code.
- (v) Colloquial for to program (that is, to write source code).
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COMM PORT |
Communications Port. 9 or 25 pin port used for bi-directional communications devices. Also newer USB ports are used as bi-directional communications ports.
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CONFIG TOOL |
Software tool from Starband used by a certified installer to set important parameters for a given VSAT system. Without the parameters set the VSAT cannot connect to the Hub and the Internet.
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CONFIGURATION |
The way a system is set up, or the assortment of components that make up the system. Configuration can refer to either hardware or software, or the combination of both. For instance, a typical configuration for a PC consists of 32MB (megabytes) main memory, a floppy drive, a hard disk, a modem, a CD-ROM drive, a VGA monitor, and the Windows operating system. Many software products require that the computer have a certain minimum configuration. For example, the software might require a graphics display monitor and a video adapter, a particular microprocessor, and a minimum amount of main memory. When you install a new device or program, you sometimes need to configure it, which means to set various switches and jumpers (for hardware) and to define values of parameters (for software). For example, the device or program may need to know what type of video adapter you have and what type of printer is connected to the computer. Thanks to new technologies, such as Plug-and-Play, much of this configuration is performed automatically.
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CONTINUOUS WAVE |
A test mode of operation of the VSAT used for co-pol and cross-pol measurements. In CW test mode, the power of the VSAT carrier is concentrated at a single frequency that allows co-pol and cross-pol measurements with a spectrum analyzer. When a VSAT is in CW test mode, hub to VSAT communication is not possible.
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CP/M |
Control Program for Microprocessors. Created by Digital Research Corporation, CP/M was one of the first operating systems for personal computers. However, Digital Research Corporation made a critical strategic error by not agreeing to produce an operating system for the first IBM PC. According to the folklore, the president of Digital Research was flying his airplane when IBM came to call. IBM marched out and never looked back. Instead, IBM turned to Microsoft Corporation, which developed MS-DOS. By the mid 1980s, MS-DOS had become the standard operating system for IBM-compatible personal computers. CP/M is now obsolete.
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CPS |
Characters Per Second, a unit of measure used to describe the speed of dot matrix and daisy wheel printers. The speed of laser and ink-jet printers is described in terms of pages per minute (ppm). CPU Central Processing Unit, and pronounced as separate letters. The CPU is the brains of the computer. Sometimes referred to simply as the processor or central processor, the CPU is where most calculations take place. In terms of computing power, the CPU is the most important element of a computer system. On large machines, CPUs require one or more printed circuit boards. On personal computers and small workstations, the CPU is housed in a single chip called a microprocessor.
- Two typical components of a CPU are:
- The arithmetic logic unit (ALU), which performs arithmetic and logical operations.
- The control unit, which extracts instructions from memory and decodes and executes them, calling on the ALU when necessary.
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CPU |
Central Processing Unit, and pronounced as separate letters. The CPU is the brains of the computer. Sometimes referred to simply as the processor or central processor, the CPU is where most calculations take place. In terms of computing power, the CPU is the most important element of a computer system.
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CRC |
Cyclic Redundancy Check, a common technique for detecting data transmission errors. A number of file transfer protocols, including Zmodem, use CRC in addition to checksum. |
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CROSS-POL |
The signal that provides an indication of the undesired signal present in the polarization opposite of the assigned polarization. This signal must be suppressed to a predefined limit so that the VSAT will not interfere with other satellite users. If the satellite provider determines that a VSAT is not operating at the required cross-pol isolation performance, the provider will require re-alignment or termination of transmissions from the offending VSAT.
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CSU/DSU |
Channel Service Unit/Data Service Unit. The CSU is a device that performs protective and diagnostic functions for a telecommunications line. The DSU is a device that connects a terminal to a digital line. Typically, the two devices are packaged as a single unit. You can think of it as a very high-powered and expensive modem. Such a device is required for both ends of a T-1 or T-3 connection, and the units at both ends must be set to the same communications standard. |
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CVACS |
Consumer Vsat Auto Commissioning System. Interactive Voice Response system designed to permit Starband installers to retrieve necessary parameters to configure the VSAT, automatically perform antenna alignment testing including co-pol and cross-pol and obtain a confirmation ID to allow the final confirmation and release process.
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DAC |
Digital Analog Converter |
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DARPA |
Defense Advanced Research Projects Agency |
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DATA |
- (1) Distinct pieces of information, usually formatted in a special way. All software is divided into two general categories: data and programs. Programs are collections of instructions for manipulating data. Data can exist in a variety of forms -- as numbers or text on pieces of paper, as bits and bytes stored in electronic memory, or as facts stored in a person's mind. Strictly speaking, data is the plural of datum, a single piece of information. In practice, however, people use data as both the singular and plural form of the word.
- (2) The term data is often used to distinguish binary machine-readable information. For example, some applications make a distinction between data files (files that contain binary data) and text files (files that contain ASCII data).
- (3) In database management systems, data files are the files that store the database information, whereas other files, such as index files and data dictionaries, store administrative information, known as metadata.
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DATA COMPRESSION |
Storing data in a format that requires less space than usual. Compressing data is the same as packing data. Data compression is particularly useful in communications because it enables devices to transmit the same amount of data in fewer bits. There are a variety of data compression techniques, but only a few have been standardized. The CCITT has defined a standard data compression technique for transmitting faxes (Group 3 standard) and a compression standard for data communications through modems (CCITT V.42bis). In addition, there are file compression formats, such as ARC and ZIP. Data compression is also widely used in backup utilities, spreadsheet applications, and database management systems. Certain types of data, such as bit-mapped graphics, can be compressed to a small fraction of their normal size. |
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DBS |
Direct Broadcast Satellites (DBS) are a subset of the domestic communications class. These satellites broadcast television or radio signals directly to subscriber's ground-based satellite dishes. |
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DECIBELS |
The unit of measurement used for magnitude of C/N readings. C/N readings are in dB and are displayed on the vertical scale of the spectrum analyzer. |
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DES |
Data Encryption Standard |
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DHCP |
Dynamic Host Configuration Protocol, a protocol for assigning dynamic IP addresses to devices on a network. With dynamic addressing, a device can have a different IP address every time it connects to the network. In some systems, the device's IP address can even change while it is still connected. DHCP also supports a mix of static and dynamic IP addresses. Dynamic addressing simplifies network administration because the software keeps track of IP addresses rather than requiring an administrator to manage the task. This means that a new computer can be added to a network without the hassle of manually assigning it a unique IP address. Many ISPs use dynamic IP addressing for dial-up users. |
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DIGITAL |
Describes any system based on discontinuous data or events. Computers are digital machines because at their most basic level they can distinguish between just two values, 0 and 1, or off and on. There is no simple way to represent all the values in between, such as 0.25. All data that a computer processes must be encoded digitally, as a series of zeroes and ones. The opposite of digital is analog. A typical analog device is a clock in which the hands move continuously around the face. Such a clock is capable of indicating every possible time of day. In contrast, a digital clock is capable of representing only a finite number of times (every tenth of a second, for example). In general, humans experience the world analogically. Vision, for example, is an analog experience because we perceive infinitely smooth gradations of shapes and colors. Most analog events, however, can be simulated digitally. Photographs in newspapers, for instance, consist of an array of dots that are either black or white. From afar, the viewer does not see the dots (the digital form), but only lines and shading, which appear to be continuous. Although digital representations are approximations of analog events, they are useful because they are relatively easy to store and manipulate electronically. The trick is in converting from analog to digital, and back again. This is the principle behind compact discs (CDs). The music itself exists in an analog form, as waves in the air, but these sounds are then translated into a digital form that is encoded onto the disk. When you play a compact disc, the CD player reads the digital data, translates it back into its original analog form, and sends it to the amplifier and eventually the speakers. Internally, computers are digital because they consist of discrete units called bits that are either on or off. But by combining many bits in complex ways, computers simulate analog events. In one sense, this is what computer science is all about. |
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DIMM |
Dual In-line Memory Module, a small circuit board that holds memory chips. A single in-line memory module (SIMM) has a 32-bit path to the memory chips whereas a DIMM has 64-bit path. Because the Pentium processor requires a 64-bit path to memory, you need to install SIMMs two at a time. With DIMMs, you can install memory one DIMM at a time. |
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DIP |
Dual Inline Package, a type of chip housed in a rectangular casing with two rows of connecting pins on either side. |
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DIP SWITCH |
A series of tiny switches built into circuit boards. The housing for the switches, which has the same shape as a chip, is the DIP. DIP switches enable you to configure a circuit board for a particular type of computer or application. The installation instructions should tell you how to set the switches. DIP switches are always toggle switches, which means they have two possible positions -- on or off. (Instead of on and off, you may see the numbers 1 and 0.) One of the historic advantages of the Macintosh over the PC was that it allowed you to configure circuit boards by entering software commands instead of setting DIP switches. However, the new Plug & Play standard developed by Microsoft makes DIP switches obsolete for PC expansion cards too. |
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DISH ANTENNA |
A reflector that concentrates a received signal back into the antenna at a focal point and focuses a transmitting signal into a beam. Normally a dish antenna will have a parabolic surface.
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DISH NETWORK |
DISHnetwork is one of the Starband partner that also sells DBS hardware and programming. |
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DISH POINT |
Software supplied with the Starband unit that gives the Az/EL and skew information for the satellite used by entering in a zip code. |
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DLL |
Dynamic Link Library, a library of executable functions or data that can be used by a Windows application. Typically, a DLL provides one or more particular functions and a program accesses the functions by creating either a static or dynamic link to the DLL. A static link remains constant during program execution while a dynamic link is created by the program as needed. DLLs can also contain just data. DLL files usually end with the extension .dll,.exe., drv, or .fon. A DLL can be used by several applications at the same time. Some DLLs are provided with the Windows operating system and available for any Windows application. Other DLLs are written for a particular application and are loaded with the application.
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DMA |
Direct Memory Access, a technique for transferring data from main memory to a device without passing it through the CPU. Computers that have DMA channels can transfer data to and from devices much more quickly than computers without a DMA channel can. This is useful for making quick backups and for real-time applications. Some expansion boards, such as CD-ROM cards, are capable of accessing the computer's DMA channel. When you install the board, you must specify which DMA channel is to be used, which sometimes involves setting a jumper or DIP switch.
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DNS |
- (1) Short for Domain Name System (or Service), an Internet service that translates domain names into IP addresses. Because domain names are alphabetic, they're easier to remember. The Internet however, is really based on IP addresses. Every time you use a domain name, therefore, a DNS service must translate the name into the corresponding IP address. For example, the domain name www.example.com might translate to 198.105.232.4. The DNS system is, in fact, its own network. If one DNS server doesn't know how to translate a particular domain name, it asks another one, and so on, until the correct IP address is returned.
- (2) Short for digital nervous system, a term coined by Bill Gates to describe a network of personal computers that make it easier to obtain and understand information.
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DOS |
Disk Operating System. The term DOS can refer to any operating system, but it is most often used as a shorthand for MS-DOS (Microsoft disk operating system). Originally developed by Microsoft for IBM, MS-DOS was the standard operating system for IBM-compatible personal computers. The initial versions of DOS were very simple and resembled another operating system called CP/M. Subsequent versions have became increasingly sophisticated as they incorporated features of minicomputer operating systems. However, DOS is still a 16-bit operating system and does not support multiple users or multitasking. For some time, it has been widely acknowledged that DOS is insufficient for modern computer applications. Microsoft Windows helped alleviate some problems, but still, it sat on top of DOS and relied on DOS for many services. Even Windows 95 sat on top of DOS. Newer operating systems, such as Windows NT and OS/2 Warp, do not rely on DOS to the same extent, although they can execute DOS-based programs. It is expected that as these operating systems gain market share, DOS will eventually disappear. In the meantime, Caldera, Inc. markets a version of DOS called DR-OpenDOS that extends MS-DOS in significant ways. |
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DOWNLINK |
1. A communications path that is used to transmit signals downward to a station on the earth from a communications satellite or aircraft.
2. To establish or utilize such a connection.
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DRAM |
Dynamic Random Access Memory, a type of memory used in most personal computers.
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DSL |
Digital Subscriber Lines, the two main categories being ADSL and SDSL. Two other types of xDSL technologies are High-data-rate DSL (HDSL) and Symmetric DSL (SDSL). DSL technologies use sophisticated modulation schemes to pack data onto copper wires. They are sometimes referred to as last-mile technologies because they are used only for connections from a telephone switching station to a home or office, not between switching stations. xDSL is similar to ISDN inasmuch as both operate over existing copper telephone lines (POTS) and both require the short runs to a central telephone office (usually less than 20,000 feet). However, xDSL offers much higher speeds - up to 32 Mbps for downstream traffic, and from 32 Kbps to over 1 Mbps for upstream traffic. |
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DSP |
Digital Signal Processing, which refers to manipulating analog information, such as sound or photographs that has been converted into a digital form. DSP also implies the use of a data compression technique. When used as a noun, DSP stands for digital signal processor, a special type of coprocessor designed for performing the mathematics involved in DSP. Most DSPs are programmable, which means that they can be used for manipulating different types of information, including sound, images, and video.
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DSS |
Digital Satellite System see also DBS. |
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DSS |
Digital Satellite System |
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DTP |
Desktop Publishing. Using a personal computer or workstation to produce high-quality printed documents. A desktop publishing system allows you to use different typefaces, specify various margins and justifications, and embed illustrations and graphs directly into the text. The most powerful desktop publishing systems enable you to create illustrations, while less powerful systems let you insert illustrations created by other programs. As word-processing programs become more and more powerful, the line separating such programs from desktop publishing systems is becoming blurred. In general, though, desktop publishing applications give you more control over typographical characteristics, such as kerning, and provide more support for full-color output. A particularly important feature of desktop publishing systems is that they enable you to see on the display screen exactly how the document will appear when printed. Systems that support this feature are called WYSIWYGs (what you see is what you get). Until recently, hardware costs made desktop publishing systems impractical for most uses. But as the prices of personal computers and printers have fallen, desktop publishing systems have become increasingly popular for producing newsletters, brochures, books, and other documents that formerly required a typesetter. Once you have produced a document with a desktop publishing system, you can output it directly to a printer or you can produce a PostScript file which you can then take to a service bureau. The service bureau has special machines that convert the PostScript file to film, which can then be used to make plates for offset printing. Offset printing produces higher-quality documents, especially if color is used, but is generally more expensive than laser printing. |
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E-MAIL |
Electronic MAIL, the transmission of messages over communications networks. The messages can be notes entered from the keyboard or electronic files stored on disk. Most mainframes, minicomputers, and computer networks have an e-mail system. Some electronic-mail systems are confined to a single computer system or network, but others have gateways to other computer systems, enabling users to send electronic mail anywhere in the world. Companies that are fully computerized make extensive use of e-mail because it is fast, flexible, and reliable. Most e-mail systems include a rudimentary text editor for composing messages, but many allow you to edit your messages using any editor you want. You then send the message to the recipient by specifying the recipient's address. You can also send the same message to several users at once. This is called broadcasting. Sent messages are stored in electronic mailboxes until the recipient fetches them. To see if you have any mail, you may have to check your electronic mailbox periodically, although many systems alert you when mail is received. After reading your mail, you can store it in a text file, forward it to other users, or delete it. Copies of memos can be printed out on a printer if you want a paper copy. All online services and Internet Service Providers (ISPs) offer e-mail, and most also support gateways so that you can exchange mail with users of other systems. Usually, it takes only a few seconds or minutes for mail to arrive at its destination. This is a particularly effective way to communicate with a group because you can broadcast a message or document to everyone in the group at once. Although different e-mail systems use different formats, there are some emerging standards that are making it possible for users on all systems to exchange messages. In the PC world, an important e-mail standard is MAPI. The CCITT standards organization has developed the X.400 standard, which attempts to provide a universal way of addressing messages. To date, though, the de facto addressing standard is the one used by the Internet system because almost all e-mail systems have an Internet gateway. In recent years, the use of e-mail has exploded. By some estimates, there are now 25 million e-mail users sending 15 billion messages per year. Another common spelling for e-mail is email.
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ECC |
Error-Correcting Code memory, a type of memory that includes special circuitry for testing the accuracy of data as it passes in and out of memory. |
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EDI |
Electronic Data Interchange As more and more companies get connected to the Internet, EDI is becoming increasingly important as an easy mechanism for companies to buy, sell, and trade information. ANSI has approved a set of EDI standards known as the X12 standards. |
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EEPROM |
Electrically Erasable Programmable Read-Only Memory. Pronounced double-ee-prom or e-e-prom, an EEPROM is a special type of PROM that can be erased by exposing it to an electrical charge. Like other types of PROM, EEPROM retains its contents even when the power is turned off. Also like other types of ROM, EEPROM is not as fast as RAM. EEPROM is similar to flash memory (sometimes called flash EEPROM). The principal difference is that EEPROM requires data to be written or erased one byte at a time whereas flash memory allows data to be written or erased in blocks. This makes flash memory faster. |
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EFT |
Electronic Funds Transfer |
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EIRP |
Equivalent Isotropically Radiated Power Telecommunications. A satellite footprint signal power level that is limited to 37 dB W by international agreement. |
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ELEVATION |
Vertical measurement in degrees from the horizon. |
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EPROM |
Erasable Programmable Read Only Memory, and pronounced ee-prom, EPROM is a special type of memory that retains its contents until it is exposed to ultraviolet light. The ultraviolet light clears its contents, making it possible to reprogram the memory. To write to and erase an EPROM, you need a special device called a PROM programmer or PROM burner. An EPROM differs from a PROM in that a PROM can be written to only once and cannot be erased. EPROM’s are used widely in personal computers because they enable the manufacturer to change the contents of the PROM before the computer is actually shipped. This means that bugs can be removed and new versions installed shortly before delivery. |
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EPS |
Encapsulated PostScript. Pronounced as separate letters, EPS is the graphics file format used by the PostScript language.
EPS files can be either binary or ASCII. The term EPS usually implies that the file contains a bit-mapped representation of the graphics for display purposes. In contrast, PostScript files include only the PostScript commands for printing the graphic. |
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EQUINOX |
The moment when the center of the sun crosses the celestial equator, in either a northbound or southbound direction. Geostationary satellites will experience a short LOSS OF SIGNAL while the sun is aligned with each satellite due to the Sun being a huge electromagnetic transmitter. See AUTUMNAL EQUINOX and VERNAL EQUINOX |
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ESD |
(1) Short for Electronic Software Distribution, a system for selling software over a network. ESD systems provide secure communications that customers use to download and pay for software. These systems can operate over the Internet or on a direct modem -to-modem connection. ESD systems can also allow users to use software for a trial period before purchasing.
(1) Short for ElectroStatic Discharge, the rapid discharge of static electricity from one conductor to another of a different potential. An electrostatic discharge can damage integrated circuits found in computer and communications equipment. |
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ESDI |
Enhanced Small Device Interface, an interface standard developed by a consortium of the leading personal computer manufacturers for connecting disk drives to PCs. ESDI is two to three times faster than the older ST-506 standard. To use an ESDI drive, your computer must have an ESDI controller. Introduced in the early 80s, ESDI is already obsolete. Instead, modern computers use a SCSI, IDE, or EIDE interface. |
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FAP |
DirecPC. Fair Access Policy. If you are a heavy downloader, DirecPC gates your bandwidth to allow others equal access through their narrow band. |
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FAQ |
Frequently Asked Questions |
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FAT |
File Allocation Table A table that the operating system uses to locate files on a disk. Due to fragmentation, a file may be divided into many sections that are scattered around the disk. The FAT keeps track of all these pieces. In DOS systems, FATs are stored in hidden files, called FAT files. The FAT system for older versions of Windows 95 is called VFAT, and the one for new versions of Windows 95 and Windows 98 is called FAT32. |
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FAX |
Telecommunications.
1. A communications system for the transmission and reception of data in graphic form over channels having a bandwidth lower than is required for video signals. An electron beam scans the image of the document to be sent and composes a digital or analog signal representing the brightness of the area under the scanning beam. The signal is then transmitted to the receiver, which reproduces the image by photographic, thermal, or xerographic techniques.
2. Also, FAX. To send a message by means of such a system. Electronics. Also, FAX MACHINE. The equipment used in this process. Graphic Arts. The graphic material produced by this process. (Short for facsimile.)
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FDD |
Fixed Disk Drive (FDD), a disk drive that can read and write to floppy disks. |
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FEED
or
FEEDHORN |
A device mounted at the focal point of the antenna that gathers signals reflected from the dish and channels these signals to the LNB through a wave-guide. |
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FILE COMPRESSION |
see DATA COMPRESSION |
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FIREWALL |
A system designed to prevent unauthorized access to or from a private network. Firewalls can be implemented in both hardware and software, or a combination of both. Firewalls are frequently used to prevent unauthorized Internet users from accessing private networks connected to the Internet, especially intranets. All messages entering or leaving the intranet pass through the firewall, which examines each message and blocks those that do not meet the specified security criteria.
There are several types of firewall techniques:
- Packet filter: Looks at each packet entering or leaving the network and accepts or rejects it based on user-defined rules. Packet filtering is fairly effective and transparent to users, but it is difficult to configure. In addition, it is susceptible to IP spoofing.
- Application gateway: Applies security mechanisms to specific applications, such as FTP and Telnet servers. This is very effective, but can impose a performance degradation.
- Circuit-level gateway: Applies security mechanisms when a TCP or UDP connection is established. Once the connection has been made, packets can flow between the hosts without further checking.
- Proxy server: Intercepts all messages entering and leaving the network. The proxy server effectively hides the true network addresses.
In practice, many firewalls use two or more of these techniques in concert. A firewall is considered a first line of defense in protecting private information. For greater security, data can be encrypted.
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FIRMWARE |
Software (programs or data) that has been written onto read-only memory (ROM). Firmware is a combination of software and hardware. ROMs, PROMs and EPROMs that have data or programs recorded on them are firmware. |
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FISHING |
Running the cable behind an interior wall using fishing tape to guide the cable. Exterior walls should never be fished. Not included in a standard basic installation. |
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FLANGE |
The protruding edge on the AZ/EL Cap Mount that is used to secure the antenna to the Cap Mount. |
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FLOW CONTROL |
(1) In communications, the process of adjusting the flow of data from one device to another to ensure that the receiving device can handle all of the incoming data. This is particularly important where the sending device is capable of sending data much faster than the receiving device can receive it. There are many flow control mechanisms. One of the most common flow control protocols for asynchronous communication is called xon-xoff. In this case, the receiving device sends a xoff message to the sending device when its buffer is full. The sending device then stops sending data. When the receiving device is ready to receive more data, it sends a xon signal. Flow control can be implemented in hardware or software, or a combination of both.
(2) In programming, the statements and other constructs that control the order in which operations are executed. For example, common looping statements such as for...next and while are known as flow control statements. Branching statements, such as if...then are also part of a programming language's flow control mechanism. |
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FM |
see FREQUENCY MODULATION |
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FOCAL POINT |
The point or area that signals are concentrated after being reflected by a parabolic surface. The feed horn is located at this point on a satellite antenna to channel the signal to the LNB. |
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FOOTPRINT |
Telecommunications. The region of the earth's surface throughout which signals may be effectively transmitted or received via a given communications satellite in a particular orbit. Computer Technology. The outline and surface area occupied by a computer and its peripheral equipment on the floor or desk top. |
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FORUM |
An online discussion group. Online services and bulletin board services (BBS's) provide a variety of forums, in which participants with common interests can exchange open messages. Forums are sometimes called newsgroups (in the Internet world) or conferences. |
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FREQUENCY |
The value displayed on the horizontal scale of the spectrum analyzer. The unit of measure used for frequency is Hertz (Hz). Commonly used multiples are kilo Hertz = kHz = 10^3 Hz, Mega Hertz = MHz = 10^6 Hz, and Giga Hertz = GHz = 10^9 HZ. |
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FREQUENCY HOPPING |
Telecommunications. A broadband modulation technique used for multiple access and interception-resistant transmission systems. |
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FREQUENCY MODULATION |
Telecommunications. FM, the instantaneous variation of the frequency of a carrier wave in response to changes in the amplitude of a modulating signal. |
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FROST HEAVE |
Movement of the ground caused by contraction and expansion above the frost line that can cause an improperly installed pole mount to shift. |
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FROST LINE |
The average depth that frost reaches in a particular area. The hole dug for a mounting post must be dug below this level to ensure that no frost will form under the cement causing frost heave. |
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FTP |
File Transfer Protocol, the protocol used on the Internet for sending files. |
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GALAXY-4 |
GE-4. Satellite that provides Starband connectivity primarily for the Northeastern region of the US. Owned by GE Americom. Located at 101 degrees.
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GATEWAY |
In networking, a combination of hardware and software that links two different types of networks. Gateways between e-mail systems, for example, allow users on different e-mail systems to exchange messages. |
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GEO |
Geosynchronous Earth Orbit |
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GEOSTATIONARY |
A satellite in circular orbit around the Earth's equator at 22300 miles altitude (36000 km) will remain stationary over the same location on Earth (i.e., the spacecraft goes around once in its orbit for every revolution of the Earth). This feature is very useful for communications satellites (allowing one satellite to provide continual coverage to a given area of the Earth's surface). As a result, the majority of satellites in geostationary orbit are commsats. Some satellites have orbits slightly higher or lower than GEO, but for simplicity sake, all satellites with apogees and perigees between 30000 and 40000 km (248000 miles) are termed GEO. |
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GEOSYNCHRONOUS |
Describes a satellite that makes one orbit around the earth every 24 hours. A satellite is both geosynchronous and geostationary if that orbit is at a fixed latitude and longitude over the equator |
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GIF |
Graphics Interchange Format, a bit-mapped graphics file format used by the World Wide Web, CompuServe and many BBSs. GIF supports color and various resolutions. It also includes data compression, making it especially effective for scanned photos. |
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GIGABYTE |
2 to the 30th power (1,073,741,824) bytes. One gigabyte is equal to 1,024 megabytes. Gigabyte is often abbreviated as G or GB. |
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GIGAHERTZ |
GHz. One billion cycles per second. See "Hertz", "Ku-band", and "L-band". |
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GOPHER |
Telecommunications. A menu-based system that searches for, retrieves, and displays information from remote servers on the Internet; developed at the University of Minnesota as a campus-wide information system |
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GROUND |
1. A connection to the earth that conducts electrical current to and from the earth. A connection to the earth that conducts electrical current to and from the earth.
2. The voltage reference point in a circuit.
3. In an electrical system, a point with zero voltage.
4. To carry out the process of grounding. |
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GROUND BLOCK |
A conducting apparatus that connects the shield (ground) of coax cable to a grounding conductor to a grounding source. |
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GROUND ROD |
A copper rod driven into the earth to serve as the ground connection. |
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HANDSHAKING |
The exchange of predetermined signals between 2 modems, computers, or other devices when a connection is established. |
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HARDWARE |
Refers to objects that you can actually touch, like disks, disk drives, display screens, keyboards, printers, boards, and chips. In contrast, software is untouchable. Software exists as ideas, concepts, and symbols, but it has no substance.
Books provide a useful analogy. The pages and the ink are the hardware, while the words, sentences, paragraphs, and the overall meaning are the software. A computer without software is like a book full of blank pages -- you need software to make the computer useful just as you need words to make a book meaningful. |
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HDD |
The mechanism that reads and writes data on a hard disk. Hard disk drives (HDDs) for PCs generally have seek times of about 12 milliseconds or less. Many disk drives improve their performance through a technique called caching. There are several interface standards for passing data between a hard disk and a computer. The most common are IDE and SCSI. |
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