Glossary of PC and Network Terminology
Use the table above to jump
to the area of the glossary containing entries beginning with the first
letter of the reference you're looking for.
Access Level.........................................
The set of permissions granted to a specific user by a computer system. Most
operating systems offer a number of built-in access levels that may be
assigned to users.
Access Point.........................................
A device that allows wireless communication devices to connect to a wireless
network using Wi-Fi, Bluetooth or related communications standards. The
access point, or AP, is typically connected to a wired network to relay data
between wireless devices (such as computers or printers) and hardwired
devices on a network.
Active Directory.....................................
A a directory service used to store information about resources across a
domain network implementation and to centralize the network. Active
Directory (AD)
was first released with Windows 2000 Server
edition, and has been revised to extend functionality and improve
administration in subsequent Windows Server operating systems. An Active
Directory structure is a hierarchical framework of objects that fall into
three broad categories: resources (e.g. printers), services (e.g. email),
and users (user accounts and groups). The AD provides information on these
objects, organizes them, controls access to them, and sets security.
AGP....................................................
Accelerated Graphics Port – a high-speed point-to-point channel for
connecting a graphics card to a computer's motherboard, primarily to assist
in the acceleration of 3D computer graphics. For graphics, AGP is superior
to PCI because it provides a dedicated pathway between the slot and the
processor (CPU) rather than sharing a bus with other peripheral cards,
allowing for faster communication. AGP also uses sideband addressing,
meaning that the address and data buses are separated so the entire packet
does not need to be read to obtain addressing information. This is
accomplished by adding eight extra buses which allow the graphics controller
to issue new AGP requests and commands at the same time with AGP data
flowing on the main 32 address/data (AD) lines. The result is improved
overall data throughput. Since 2004, AGP is being progressively phased out
in favor of PCI Express. However, as of mid 2008 new AGP cards and
motherboards are still available for purchase, but OEM driver support has
become minimal.
Application Software...............................
Programs written to perform specific functions, such as word processing,
database management, or graphics editing. Most PC's are configured with
several different types of application software to provide a wide range of
functionality.
ASCII...................................................
American Standard Code of Information Interchange – a coding standard can be
used for transferring information. ASCII codes represent text in computers,
communications equipment, and other text-processing devices. Most modern
character-encoding schemes - which support more characters than the original
128-character set - are based on extensions of ASCII.
ATA....................................................
Advanced Technology Attachment – an interface standard for the connection of
storage devices such as hard disk drives. The ATA standard has been extended
to cover to both parallel ATA (PATA) and serial ATA (SATA) devices.
ATAPI..................................................
Advanced Technology Attachment Packet Interface – an evolution of the ATA
interface standard that was developed primarily to satisfy the needs of
removable storage devices, such as
optical drives, which require the
support of a "Media Eject" command and a method for determining the presence
or absence of media in these drives.
BIOS...................................................
Basic Input Output System – the a de facto standard defining a firmware
interface for IBM PC Compatible computers. The BIOS is boot firmware, and is
the first code to be run by a PC when it is powered on. The BIOS identifies,
tests, and initializes system devices such as the video display card, hard
disk, optical drive, and other hardware. This places the machine into a
known state, so the software stored on the computer's media can be loaded,
executed, and given control of the PC. This process is known as booting, or
booting up, which is short for bootstrapping.
Cable Modem........................................
A device for connecting a home or small office computer or network to the
Internet through a cable service provider.
CAT5/CAT6..........................................
The type of cable used in most small hardwired networks. This type of cable
contains 8 separate wires twisted into 4 pairs inside an outer jacket, and
is usually terminated by 8-pin RJ-45 snap-in type connectors.
COM (1)..............................................
COMmunications – the standard abbreviation for a serial communications port
on a PC or other device. The COM designation may include a digit indicating
the ordinal number of the particular port, e.g. COM1 for a PC's first serial
port.
COM (2)..............................................
Component Object Model – an interface standard for software components that
was introduced by Microsoft in 1993. COM is used to enable inter-process
communication and dynamic object creation within a large range of
programming languages. COM is essentially a language-neutral way of
implementing objects that can be used in environments different from the
ones in which they were created, even across machine boundaries. COM enables
the reuse of objects with no knowledge of their internal implementations,
because it forces component implementers to provide well-defined interfaces
that are separate from the implementations.
CPU...................................................
Central Processing Unit – a microprocessor that functions as primary
processing unit of a PC. Newer CPU's are typically constructed with multiple
cores to enable faster overall PC performance through parallel program
execution.
CRT...................................................
Cathode Ray Tube – the type of technology used to produce older tube-style
computer monitors.
Database.............................................
A repository for statistical and
configuration data. A database is a
large file containing one or more tables of related information.
DCOM.................................................
Distributed Component Object Model – a proprietary Microsoft technology for
communication among software components distributed across networked
computers. DCOM has been deprecated in favor of the Microsoft .NET
framework.
DDE....................................................
Dynamic Data Exchange – a technology for communication among multiple
applications running under Microsoft Windows or OS/2. DDE is a generic
protocol that allows any application to monitor changing data provided by
any other application, and the primary function of DDE is to allow Windows
applications to share data. For example, a cell in a Microsoft Excel
spreadsheet may be linked to a value in another application, and the value
automatically updated whenever it is changed in the other program.
DDR....................................................
Double Data Rate – a class of memory integrated circuits used in computers.
DDR memory achieves nearly twice the bandwidth of the preceding "single data
rate" memory by double pumping, i.e. transferring data on both the rising
and falling edges of the clock signal without increasing the memory bus
clock frequency. With data being now being transferred 64 bits at a time,
DDR memory enables a transfer rate of (memory bus clock rate) × 2 (for dual
rate) × 64 (number of bits transferred) / 8 (number of bits/byte). For a
memory bus frequency of 100 MHz, DDR SDRAM provides a maximum transfer rate
of 1600 MB/sec.
DDR2..................................................
Double Data Rate 2 – a random access memory technology used for high
bandwidth storage of the working data of a computer or other digital
electronic device. DDR2 is an evolutionary improvement
over its predecessor, DDR SDRAM. DDR2
memory offers reduced power consumption compared to DDR due to DDR2's 1.8V
vs. DDR's 2.5V. However, DDR2's primary benefit is its
ability to operate with an external data bus running at a frequency twice
that of DDR. This is acomplished by improved bus signaling and by operating
the memory cells at half the clock rate, rather than at the actual clock
rate as required by DDR. DDR2 memory, when operated at twice the external
data bus clock frequency of DDR, is able to provide twice the bandwidth with
the same latency. However, DDR2 memory when operated at the same external
data bus clock rate as DDR will provide the same bandwidth with markedly
higher latency, providing inferior performance, since the memory cells are
operating at half the rate.
DDR3..................................................
Double Data Rate 3 – a random access memory technology used for high
bandwidth storage of working data in a computer or other digital electronic
device. DDR3 improves on its predecessor, DDR2 SDRAM by its ability to
transfer twice the data rate of DDR2 (I/O at 8X the data rate of the memory
cells it contains), enabling higher bus rates and higher peak rates than
earlier memory technologies. DDR3
memory also provides a reduction in
power consumption of 30% compared to DDR2 due to DDR3's 1.5V supply voltage
requirement, compared to DDR2's 1.8V. The DDR3 standard also allows for chip
capacities of 512 megabits to 8 gigabits, effectively enabling a maximum
memory module sizes of up to 16 GB (gigabytes).
DIMM..................................................
Dual Inline Memory Module – a series of dynamic random access memory
integrated circuits mounted on a printed circuit board and designed for use
in personal computers, workstations and servers. DIMM's began to replace
SIMM's (Single Inline Memory Modules) as the predominant type of PC memory
module when Intel's Pentium processors began to gain market share. DIMM's
have separate electrical contacts on each side of the module, while the
contacts on both sides
of SIMM's are redundant. Also, standard
SIMM's are constructed with 32-bit data paths, while standard DIMMs have
64-bit data paths to match the data bus widths of most newer processors.
DMA...................................................
Direct Memory Access – a design feature of modern computers and
microprocessors that enables some hardware subsystems within the PC to
access main system memory independently of the central processing unit.
DMA is employed to transfer data between
local device memory and main memory.
Hardware components such as disk controllers, graphics cards, network cards,
and sound cards are often capable of
employing DMA. Without DMA, using
programmed input/output (PIO) mode for communication with these devices, the
computer's CPU is typically fully occupied for the entire duration of the
read or write operation, rendering it unable to perform other processing.
Consequently, PC's equipped with DMA channels are able to transfer data
to/from these devices with far less CPU overhead than computers without DMA
channels. DMA is also used for intra-chip data transfer within multi-core
processors, where each processing unit is equipped with a local "scratchpad"
memory. A processing unit inside the
multi-core processor can transfer data to and from its local memory without
requiring any processor time, allowing overlap between computation and data
transfer.
DNS....................................................
Domain Name System – the protocol used by Internet name servers. A domain
name server is a server that governs the DNS records, such as A-records
(host records), MX-records (mail
exchange records), and CNAME-records
(aliases) for a domain name. A DNS server
maps a human-readable host identifier, for example, the domain name "maxpcinc.com,"
to its corresponding machine-readable identifier, such as its IP address,
and vice versa. Every domain name must have a primary name server, e.g.
ns1.domainname.com, and at least one secondary name server
(ns2.domainname.com etc). This requirement is intended to ensure the domain
is still reachable if one name server becomes unreachable. Most small local
area networks of Windows computers require no central name server, and
generally perform name-resolution via broadcasts.
Domain...............................................
A type of Windows network that provides centralized services and
enhanced security features. The implementation of a domain requires the
installation of a computer running one of the Windows Server
operating systems and the computer's configuration as a Domain Controller.
Typically, medium to large networks are configured as domains, while smaller
networks are configured as workgroups.
Domain Controller.................................. A computer running a Windows server
operating system that has been configured to provide the centralized
services and security features for a Domain.
DRAM..................................................
Dynamic Random Access Memory – the memory type most commonly used as main
memory for computers. DRAM is a volatile type of memory, and loses its
stored data if power is lost. DRAM memory modules are available in a number
of different physical and electrical configurations, and the type installed
in any specific PC must be matched to its main board and BIOS capabilities.
See also RAM.
Drive..................................................
A device for reading (and typically also writing) to some type of secondary
storage medium, such as a magnetic disk, optical disc, or tape. Depending on
its design, a drive supports either removable media (e.g. optical disc) or
non-removable media (e.g. hard disk).
DSL....................................................
Digital Subscriber Line – a family of technologies designed to provide
digital data transmission over the wires of a local telephone network. DSL
supports simultaneous voice and data transmission on the same telephone
line, enabling always-on Internet connectivity.
The download speed of DSL service ranges from 256 kilobits per second to
24,000 kb/s, depending on DSL technology, line conditions and service level.
Upload speed is generally lower than download speed for Asymmetric Digital
Subscriber Line (ADSL) and equal to download speed for the less common
Symmetric Digital Subscriber Line (SDSL). Phone companies offer DSL service
in many, but not all, areas.
DSL
Modem.......................................... A device for connecting
a home or small office computer or network to the internet through a phone
service provider via a dedicated digital subscriber line (DSL).
DVI....................................................
Digital Visual Interface – a video interface standard designed to maximize
the visual quality of digital display devices such as flat panel LCD
computer displays and digital projectors. DVI was designed to transfer
uncompressed digital video data to a display. Digital mode DVI (DVI-D)
is partially compatible with the High-Definition Multimedia Interface
standard, and analog mode DVI (DVI-A) is compatible with VGA.
EISA...................................................
Extended Industry Standard Architecture – an older communications bus standard
for the connection of peripheral cards to a PC motherboard. The original
1988 standard grew out of the original ISA standard and expanded the bus
width to an 32-bit bus to enable more than one CPU to share the bus. Bus
mastering support was also enhanced over ISA, providing direct memory access
of 4 GB of memory. The EISA bus can accept older XT and ISA boards, as the
lines and slots for EISA are a superset of ISA. See also ISA.
Ethernet..............................................
A packet-based protocol and transport medium used for communication
between devices connected over a local area network.
Ethernet Media
Adapter...........................
A device that converts Ethernet communications from one transport medium to
another, e.g. from a twisted-pair cable to a shielded coaxial cable.
FireWire.............................................
The name adopted by Apple, Inc for its implementation of the IEEE 1394
serial bus interface standard. FireWire
is available in hardwired, wireless, fiber optic, and coaxial versions using
the isochronous protocols. FireWire can connect up to 63 peripherals in a
tree topology. It allows peer-to-peer device communication, such as
communication between a scanner and a printer, to take place without using
system memory or the CPU. FireWire also supports multiple hosts per bus. It
is designed to support Plug and play and hot swapping. See also IEEE 1394.
Gateway..............................................
A network point where two or more networks are connected. Typically, a
router occupies the network gateway.
GUI....................................................
Graphical User Interface – a pointer-based type of Human-Machine Interface
that uses “mouse” clicks, rather than text entered via keyboard, for command
input.
HDCP..................................................
High-bandwidth Digital Content Protection – a form of digital copy
protection developed by Intel to prevent the copying of digital audio and
video content as it travels across
connections, such as Digital Visual
Interface or High-Definition Multimedia Interface connections, even if such
copying would be permitted by fair use laws. The specification is
proprietary, and implementing HDCP requires a license. PC-based playback of
movies is generally not possible without HDCP-licensed equipment.
HDMI...................................................
High Definition Multimedia Interface – an audio/video interface standard
designed to transfer uncompressed digital data. HDMI represents a digital
alternative to consumer analog standards, such as radio frequency (RF)
coaxial cable, composite video, S-Video, component video, and VGA. HDMI
connects digital audio/video sources such as set-top boxes, Blu-ray Disc
players, personal computers (PCs), video game consoles, and AV receivers to
compatible digital audio devices, computer monitors, and digital
televisions. On a single cable, HDMI supports any TV or PC video format,
including standard, enhanced, and high-definition video, up to 8 channels of
digital audio, and a Consumer Electronics Control signal.
HMI....................................................
Human-Machine Interface – the boundary where a human operator and a machine
interact with one another.
Hot-swappable ......................................
The ability of a device to be connected and disconnected
to/from a PC without having to restart the computer or cycle power to the
device. USB devices are typically hot-swappable.
HTML..................................................
Hyper-Text Markup Language – the predominant markup language for Web pages.
HTML provides a means to describe the structure of text-based information in
a document — by denoting certain text as links, headings, paragraphs, lists,
and so on — and to supplement that text with interactive forms, embedded
images, and other objects. HTML script is written in the form of tags,
surrounded by angle brackets. HTML can also describe, to some degree, the
appearance and semantics of a document, and can also include embedded
scripting language code, such as JavaScript, which affect the behavior of
Web browsers and other HTML processors.
Hub....................................................
A passive network device to which two or more computers, print servers, and
other devices may be connected for high-speed communication. The bandwidth
of each of the hub's ports decreases as the number of network devices
increases. Hubs do not amplify the electrical signal of incoming
communication packets before broadcasting them out to the network. Ethernet
switches, on the other hand, do perform this amplification, as does a
network repeater.
Icon....................................................
A graphical representation of a button, application program, or piece of
equipment that is used to convey commands to a computer, for example
printing a file.
IDE.....................................................
Integrated Drive Electronics – the PC drive interface developed by Western
Digital, and still informally applied to more recent drive interface
standards, such as ATA and ATAPI. However, this is imprecise at best, since
all ATA/ATAPI drives are "integrated drive electronics" devices, but not
every "integrated drive electronics" drive is an ATA/ATAPI device. SCSI
drives also have have integrated drive controllers.
IEEE 1394............................................
a serial bus interface standard developed by the Institute for Electrical
and Electronics Engineers for high-speed communications and isochronous
real-time data transfer. IEEE 1394 is used by many personal computers, as
well as in digital audio, digital video, automotive, and aeronautics
applications. The interface standard is often referred to by one of its
brand names, such as FireWire (Apple), i.LINK (Sony), and Lynx (Texas
Instruments). IEEE 1394 replaced parallel SCSI in many applications, because
of lower implementation costs and a simplified, more adaptable cabling
system, and has been adopted as the High Definition Audio-Video Network
Alliance (HANA) as the standard connection interface for A/V (audio/visual)
component communication and control. The 1394 standard also defines a
backplane interface, though this is not as widely used.
IPsec..................................................
Internet Protocol security – a suite of protocols for securing Internet
Protocol (IP) communications through the authentication and encryption of
each IP packet in a data stream. IPsec also includes protocols for
establishing mutual authentication between agents at the beginning of each
session and negotiation of cryptographic keys to be used during the session.
IPsec can be used to protect data flows between a pair of hosts, such as
computer users or servers, between a pair of security gateways, such as
routers or firewalls, or between a security gateway and a host. IPsec is a
dual mode, end-to-end, security scheme operating at the Internet Layer of
the Internet Protocol Suite. It is more flexible that those, such as Secure
Socket Layer (SSL) and Transport Layer Security (TLS), that operate at
higher levels, because it can be used to protect a wider range of traffic.
Applications need not be designed to use IPsec, as they must in order to
implement TLS/SSL and other higher-layer protocols.
IPX/SPX..............................................
Internet Packet eXchange/Sequenced Packet eXchange – a communication
protocol suite that provides connection services similar to TCP/IP, with the
IPX protocol services being similar to IP services, and those of SPX similar
to TCP. IPX/SPX was designed primarily
for local area networks. It is extremely
efficient for this purpose, and its performance typically exceeds that of
TCP/IP on a LAN. Some older operating systems run NetBIOS over IPX/SPX.
However, TCP/IP has become the de facto standard communication protocol
suite, in part due to its superior performance over wide area networks and
the Internet, which uses TCP/IP exclusively.
IRQ....................................................
Interrupt ReQuset – the interrupt input lines on a Programmable Interrupt
Controller (PIC) or the act of interrupting these lines. Interrupt lines are
often identified by an index using the format of IRQ followed by a number.
For example, the COM1 serial port is traditionally assigned to IRQ4. Each
PIC can accommodate 8 distinct interrupts (IRQ0 through IRQ7), and newer
x86-based computer systems, which use two PIC's, combine their sets of lines
to support IRQ0 through IRQ15. The newest x86 systems employ Advanced
Programmable Interrupt Controllers (APIC's) that support up to 255 physical
hardware IRQ lines per APIC, and a typical system implements support for
approximately 24 total hardware lines.
ISA.....................................................
Industry Standard Architecture – an older communications bus standard
developed to connect peripheral cards to a PC motherboard. The original 1981
standard consisted of an 8-bit bus, but was expanded in 1984 to a 16-bit bus
to support the new PC AT architecture. The ISA bus was synchronous with the
CPU clock until sophisticated buffering methods were later developed and
implemented by chipsets to interface ISA to much faster CPUs. Bus mastering
and Direct Memory access (DMA) were supported, but could use only the first
16 MB of main memory for DMA operations. Users of ISA-based machines had to
know specific information about the hardware they were adding to the system,
such as the IRQ line, I/O address, or DMA channel.
A handful of devices were essentially "plug-n-play," but this was rare.
ISP.....................................................
Internet Service Provider – a company that provides a connection to the
internet. ISP's may provide either dial-up or broadband Internet
connectivity.
Keyboard.............................................
A device used to input alphanumeric characters to a computer.
LAN....................................................
Local Area Network – a network of computers or similar devices connected
together, typically via a hub or switch, by high-speed communication cables.
LCD....................................................
Liquid Crystal Display – the type of technology used to produce the majority
of flat screen computer monitors.
Login
(or Logon)..................................... The process of
gaining access to a secure or multi-user computer.
MCA...................................................
Micro-Channel Architecture – a proprietary 16-bit or 32-bit parallel
computer bus created by IBM in the 1980s for use in the company's "PS/2"
computers. For a time, MCA could be found in IBM RS/6000 and AS/400
computers, and even some of the company's System/370 mainframes, as well as
its PS/2 computers. However, most of these systems later were redesigned to
incorporate PCI. MCA is no longer used in new designs.
MDAC.................................................
Microsoft Data Access Components – a framework of interrelated Microsoft
technologies that enables programmers a uniform and comprehensive way of
developing applications that can access almost any data store. Its
components include: ActiveX Data Objects (ADO), OLE DB, and Open Database
Connectivity (ODBC).
Mouse.................................................
A moveable pointer-based device used to input commands to a computer.
NetBIOS...............................................
Network Basic Input-Output System – an application programming interface
(API) that allows programs on different computers to communicate with one
another over a local area network. In modern networks, NetBIOS normally runs
over TCP/IP (NetBIOS over TCP/IP, or NBT), providing each computer on the
network with a NetBIOS name. Whenever NetBIOS is run over TCP/IP, each
computer will have multiple "names" — a names for the NetBIOS API,
a possibly different host name, plus
another or others for basic TCP/IP services. A Windows machine's NetBIOS
name should not be confused with the computer's host name. In general, any
computer running TCP/IP (whether it's a Windows machine or not) is assigned
a host name, also referred to as a machine name or a DNS name. Usually, the
host name of a Windows computer is based on its NetBIOS name plus its
Primary DNS Suffix. In order to connect a computer running the TCP/IP
protocols to a network using its HOST name, the host name must be resolved
into an IP Address. IP address resolution of the host name, or Fully
Qualified Domain Name (FQDN), is typically performed by a Domain Name System
(DNS) server.
OCR....................................................
Optical Character Reader – a unit capable of translating optically scanned
characters into ASCII text.
ODBC..................................................
Open Data Base Connectivity – a standard software application programming
interface (API) method for using database management systems (DBMS). The
goal of ODBC
is to make it independent of programming
languages, database systems, and operating systems. An
ODBC
implementation contains one or more applications, a core ODBC "Driver
Manager" library, and one or more "database drivers". The Driver Manager,
which is independent of the applications and DBMS, acts as the "interpreter"
between the application software and the database drivers, while the
database drivers contain the DBMS-specific details.
OLE....................................................
Object Linking & Embedding – a technology that enables embedding and linking
to documents and other objects developed by Microsoft. This
brought developers OLE
custom controls (OCX), a method for
developing and implementing custom user interface elements. The primary use
of OLE is in managing compound documents, but it is also used for
transferring data between different applications using drag and drop and
clipboard operations. Also, the concept of "embedding" is central to the use
of multimedia in Web pages, which tend to embed video, animation, and audio
files within the hypertext markup language.
Operating System...................................
The underlying computer software that provides basic
services, such as memory and storage management, application execution, task
switching, and input/output functionality.
PATA...................................................
Parallel Advanced Technology Attachment – the
acronym now
applied to parallel storage devices that conform to ATA interface standard.
Refer to the ATA standard above.According
to the ATA standard, PATA ribbon cables must be no longer than 18 inches,
making the use of parallel ATA for external devices impossible in most
situations. Pin 20 of the ribbon connector cable is defined as a key and is
not used. However, some flash memory disks can use pin 20 to power the disk
without needing a separate power cable. Pin 28 of an 80 conductor cable is
normally attached to a wire at the black master drive and blue motherboard
end connectors, but not at the gray slave middle connector. Pin 34 of an 80
conductor cable is connected to ground inside the blue (motherboard)
connector but to any conductor of the cable. It is attached normally on the
gray and black connectors.
PCI.....................................................
Peripheral Component Interconnection – a communications bus standard
commonly used in personal computers. The PCI bus provides communication
between peripheral devices and the CPU. This is a parallel data bus with a
32-bit width. Common PCI bus components include network interface cards,
modems, TV tuner cards, and sound cards.
PCI-E (or PCIe).......................................
Peripheral Component Interconnection Express – a communications bus standard
designed to replace the older PCI, PCI-X, and AGP standards in personal
computers. Introduced in 2004, PCI Express is used in consumer, server, and
industrial applications, both as a main board-level interconnect (to link
motherboard-mounted peripherals) and as an expansion card interface for
add-in boards. A key difference between PCIe and earlier PC buses is a
topology based on point-to-point serial links, rather than a shared parallel
bus architecture.
PCI-X..................................................
Peripheral Component Interconnection eXtended – a communications bus
standard commonly used in personal computers. The PCI bus is a double-wide
version of PCI, running at up to four times the clock speed, but is
otherwise similar in electrical implementation. This is a parallel data bus
with a 64-bit width. PCI-X was devised to support devices - most notably
Gigabit Ethernet cards, Fibre Channel and Ultra320 SCSI controllers, and
cluster interconnects - that could, by themselves, saturate the full
bandwidth of a standard PCI bus.
Phone Modem........................................
A phone modem, or simply modem, is a device for connecting a home or small office computer to the Internet through a
telephone service provider.
Port....................................................
A physical interface through which data transfers in or out of a PC.
Examples of ports are network, serial, parallel, SCSI, USB, Fire Wire, and
graphics (video) ports.
RAID...................................................
Redundant Array of Inexpensive Disks – a multiple hard disk configuration to
improve fault tolerance (reliability) and/or speed in a computer. A RAID
combines two or more physical hard disks into a single "logical unit," and
creating a RAID involves mirroring and/or striping disk contents. The RAID-1
array configuration is most common in PC's and provides hardware fault
tolerance against the failure of one physical disk. Implementing a RAID
requires the installation of a RAID controller, if one is not already
present in the PC.
RAM....................................................
Random Access Memory – a type of memory that allows data to be accessed in
any order (at random). In this
context, random refers to the fact
that any piece of data can be stored or retrieved in a constant time,
regardless of its physical location and whether or not it is related to the
previous piece of data. The term "RAM" is generally associated with volatile
types of memory, such as DRAM memory modules, in which the data is lost if
power is lost. However, many other types of memory also support random
access, including most types of ROM and flash memory.
Repeater..............................................
A network device that amplifies received network signals and retransmits
them at a higher level and/or higher power, enabling the signals to cover
longer distances without degradation.
A repeater may be either wired or wireless in design.
ROM....................................................
Read-Only Memory – a type of memory in which
stored
data cannot be very quickly or easily
modified, if at all. ROM is primarily used to
distribute firmware (software that is very closely tied to specific
hardware, and unlikely to require frequent updates).
Router.................................................
A network device that forwards data across at least two networks, typically
two different LANS, or a LAN and a WAN, such the Internet via a cable modem.
A router may be either wired or wireless in design.
RTC....................................................
Real Time Clock – a computer clock, often in the form of an integrated
circuit, that keeps track of the current time. Although the term often
refers to the devices in personal computers, servers and embedded systems,
RTCs are present in almost any electronic device which needs to keep
accurate time. Most RTC's use crystal oscillators, although a few use the
power line frequency. In many cases the oscillator's frequency is 32.768
kHz, which is the same frequency used in quartz clocks and watches, and for
the same reason, i.e. that the frequency is exactly 215
cycles per second, which is a convenient rate to use with binary circuits.
Computer RTCs have an alternate source of power to enable them to continue
keeping time when the primary power
source is unavailable. This alternate
source of power is generally a lithium battery, but some newer systems use
capacitors, because they are rechargeable and can be soldered to the
motherboard.
Scanner..............................................
A device for optically inputting photos and other graphical information into
a computer.
SATA..................................................
Serial Advanced Technology Attachment – an extension of the ATA interface
standard for the connection of serial storage devices. Refer to the ATA
standard above.
SCSI...................................................
Small Computer System Interface – a set of communications standards for
connecting and transferring data between computers and peripheral devices.
SCSI standards define commands, protocols, and electrical and optical
interfaces. SCSI is most commonly used for hard disks and tape drives, but
it can connect a wide range of other devices, including scanners and CD
drives.
SDRAM................................................
Synchronous Dynamic Random Access Memory – a type of
random access
memory that uses a synchronous interface.
Dynamic random access memory (DRAM) has traditionally used an asynchronous
interface, meaning it responds as quickly as possible to changes in control
inputs. In contrast, SDRAM waits for a clock signal before responding to
control inputs and is therefore synchronized with the computer's system bus.
The clock is used to drive an internal finite state machine that pipelines
incoming instructions. This allows the chip to have a more complex pattern
of operation than asynchronous DRAM.
SGML.................................................
Standard Generalized Markup Language – an ISO Standard meta-language that
enables programmers to define markup languages for documents. SGML was
originally designed to allow sharing of machine-readable documents in large
projects in government, law and industry, which must remain readable for
several decades - a very long time in information technology. SGML has also
been used extensively in the printing and publishing industries, but its
complexity has prevented its widespread application for small-scale
general-purpose use. Although SGML allows most aspects of a markup
language's syntax to be customized, HTML uses the
default
SGML syntax.
SIMM..................................................
Single Inline Memory Module – a type of
random access
memory module used in computers from the
early 1980's to the late 1990's. SIMM's were the predominant memory type for
processors using up to 32-bit data buses, but have subsequently been
replaced by DIMM's (Dual Inline Memory Modules) primarily to accommodate
the 64-bit data bus widths of most newer processors. While SIMM's were used
for a while with the newer processors, they had to be installed in matched
pairs in order to complete the data bus, and the processor would then access
two SIMM's simultaneously. Unlike DIMM's, SIMM's are constructed with
redundant contacts on both sides of the modules.
SSD....................................................
Solid-State Drive – A drive with no moving parts. Although the SSD interface
mimics that of a conventional hard disk drive, this type of drive uses
static memory, rather than a magnetic disc spinning under a read/write head
to store and retrieve data. The inherent ruggedness of SSD's is their
primary advantage over conventional drives for use in portable applications
and in hostile environments. The write speeds of SSD designs still lag those
of conventional hard disks, but SSD's are becoming faster with each new
generation. However, their relatively high cost per unit of storage, the
limited number of write cycles supported by the memory used in SSD's, and
their gradual performance degradation with use must be overcome before they
can be expected replace electro-mechanical drives.
SSL....................................................
Secure Socket Layer – The SSL protocol was originally developed by Netscape.
Like its successor, Transport Layer Security (TLS), SSL is a cryptographic
protocol for ensuring the security and data integrity of communications over
TCP/IP networks such as the Internet. Also like TLS, SSL encrypts the
segments of network connections at the Transport Layer from end to end, and
like TLS, several versions of the protocol are in wide-spread use in
applications such as web browsing, electronic mail, Internet faxing, instant
messaging and voice-over-IP (VoIP). Message authentication codes
for SSL are made up from a
non-standard pseudorandom function.
Switch................................................
An active network device to which two or more computers or similar machines
may be connected for high-speed communication. Unlike a hub, a switch
provides full rated bandwidth on every port.
Ethernet switches, unlike hubs, also amplify the electrical signal of
incoming communication packets before broadcasting them out to the network.
TCP/IP................................................
the set of communications protocols used for the Internet and other
networks. Its name is a combination of two important communication
protocols: the Transmission Control Protocol (TCP) and the Internet Protocol
(IP), which were the first two networking protocols defined in this
standard. The TCP/IP Suite defines a set of rules to enable computers to
communicate over a network. TCP/IP provides end-to-end connectivity by
specifying how data should be formatted, addressed, transmitted, routed and
delivered to the correct destination. The specification defines protocols
for different types of communication between computers and provides a
framework for more detailed standards. TCP/IP uses encapsulation to provide
abstraction of protocols and services. Such encapsulation usually is aligned
with the division of the protocol suite into layers of general
functionality. In general, an application (the highest level of the model)
uses a set of protocols to send its data down the layers, being further
encapsulated at each level.
TLS...................................................
Transport Layer Security – a cryptographic protocol designed to provide
security and data integrity for communications over TCP/IP networks such as
the Internet. TLS encrypts the segments of network connections at the
Transport Layer end-to-end. TLS is the successor to the Secure Socket Layer
(SSL) protocol, and like SSL, several versions of TLS are in wide-spread
use. The TLS protocol enables client/server applications to communicate
across a network in a way designed to prevent eavesdropping, tampering, and
message forgery.
Touch-screen.......................................
A device that translates screen touches to “mouse” clicks for operator input
to a system.
Trackball............................................
A stationary pointer-based device that simulates mouse actions to input
commands to a computer.
UPS...................................................
Uninterruptible Power Supply – a device that is capable of providing power
from its battery if building power fails. The length of time a UPS is able
to continue providing power depends on both the capacity of its battery and
the current drain at its battery-backed-up outlets. Typically, this period
is only five (5) to ten (10) minutes. However,
each UPS is usually shipped with
a supervisory program that can enable a
graceful automatic PC shutdown before battery power is depleted.
USB...................................................
Universal Serial Bus – A high speed serial communications bus standard
commonly used to connect external devices to personal computers. A USB port
supports much higher data throughput than a standard serial port and
generally allows "hot-swapping" of devices. Printers, optical scanners,
flash drives, media players, cameras, and many other external devices
commonly connect to PC's via USB connections. USB was designed to allow many
peripherals to be connected using a single standardized interface socket and
to improve plug and play capabilities by allowing hot swapping, i.e.
allowing devices to be connected and disconnected without rebooting the
computer or turning off the device. Other convenient USB features include
providing power to low-consumption devices, eliminating the need for an
external power supply; and allowing many devices to be used without
requiring manufacturer-specific device drivers to be installed.
VGA...................................................
Video Graphics Array – the display hardware standard first introduced with
the IBM PS/2 line of computers in 1987. Through its widespread adoption VGA
has also come to mean either an analog type
computer display, the 15-pin D-subminiature VGA connector, itself, or the
standard 640×480 VGA resolution. For PC use, the VGA standard has been
superseded by a number of slightly different extensions to VGA made by
various manufacturers that came to be known collectively as "Super VGA."
Although VGA resolution is no longer commonly used for personal computers,
it is a popular resolution on many mobile devices.
VPN...................................................
Virtual Private Network – a computer network in which some of the links
between nodes are carried by open connections or virtual circuits in some
larger network, e.g., the Internet, instead of running across a single,
monolithic private network. The link-layer protocols employed by the VPN are
said to be tunneled through the larger network. A common application is
secure communications through the public Internet, but a VPN need not have
explicit security features, such as authentication or content encryption.
From a security standpoint, a VPN must either trust the underlying delivery
network or must enforce security with mechanisms within the VPN itself.
Unless the trusted delivery network runs only among physically secure sites,
both trusted and secure models need an authentication mechanism for users to
gain access to the VPN. Secure VPNs use cryptographic tunneling protocols to
provide the intended confidentiality (blocking snooping and packet
sniffing), sender authentication (blocking identity spoofing), and message
integrity (preventing message alteration) to achieve privacy. When properly
selected, implemented, and executed, such techniques can provide secure
communications over unsecured networks.
WAN..................................................
Wide Area Network – a network of computers or similar devices connected
together over large distances. A WANs is used to connect LANs and other
types of networks together, so that users and computers in one location can
communicate with users and computers in other locations.
WLAN.................................................
Wireless Local Area Network – a network of computers or similar devices
connected together wirelessly, usually via a wireless router, and possibly additional
wireless access points. This enables users to move around within the
coverage area without losing connectivity with the network.
Workgroup..........................................
A type of Windows network that that does not require a Domain
Controller and does not provide centralized services or enhanced security
features. A workgroup is the type of network implemented for most home and
small business networks. Although less secure than domains, workgroups still
enable printer and file sharing among the PC's on the network.
XML...................................................
eXtensible Markup Language – a general-purpose specification for the
creation of custom markup languages. XML is classified as an extensible
language, because it allows the user to define the markup elements. Its
purpose is to aid information systems in sharing structured data, especially
via the Internet, to encode documents, and to serialize data. XML is
recommended by the World Wide Web Consortium (W3C), and it is a fee-free
open standard. XML's set of tools assists developers in creating web pages,
but its usefulness extends well beyond that use. XML, in combination with
other standards, makes it possible to define the content of a document
separately from its formatting, facilitating the reuse of that content in
other applications or for other presentation environments. XML provides a
basic syntax that can be used to share data among different kinds of
computers and different applications without requiring the data to pass
through many layers of conversion.
