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Radio button
A form field that presents a user with a selection that can be chosen by clicking on a button. Radio buttons are
presented in a list, one of which is selected by default. Selecting a new member of the list deselects the currently
selected item. See also check box.
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RAID (Redundant Array of Inexpensive Disks)
RAID is a configuration of multiple disks designed to preserve data after a disk casualty.
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RAM (Random Access Memory)
RAM is the working memory of a computer where data and programs are temporarily stored. RAM only holds information
when the computer is on. So, RAM is a data storage device for which the order of access to different locations
does not affect the speed of access. This is in contrast to magnetic disk or magnetic tape where it is much quicker
to access data sequentially because accessing a non-sequential location requires physical movement of the storage
medium rather than just electronic switching. The most common form of RAM in use today is built from semi-conductor
integrated circuits, which can either be static (SRAM) or dynamic (DRAM).
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RAP - DQRAP (Distributed Queueing Random Access Protocol)
DQRAP was originally developed by Xu [90] as part of a directed research project to develop a multiple access protocol
that would permit hundreds if not thousands of users to share a single data channel on a typical CATV cable system.
DQRAP, however, has shown promise in a number of other environments and that DQRAP is suited for use in both third
generation cellular phone systems and general purpose wireless data systems.
DQRAP offers very good performance, in fact the performance with respect to both delay and throughput approaches
that of ideal M/D/1 or M/M/1 systems depending upon whether fixed or variable length slots are used [Xu and Campbell
93]. The model used consists of a base and an infinite number of terminal stations. The basic transmission time
is a slot which consists of a dataslot, which holds the packet, and m control minislots which are used to schedule
transmission of the packets. In practice the number of minislots is 3. Terminals exchange information by transmitting
in a control minislot and/or dataslot. The base station broadcasts the results of these received transmissions
back to all the terminals.
DQRAP operates by providing two servers: a data server and a collision resolution server. Every station in the
system maintains two queues: the collision resolution queue RQ, and the data transmission queue TQ. The TQ controls
access to the data server (the data slots) while the RQ controls access to the collision resolution server (the
minislots). A key requirement of DQRAP is that ternary feedback be provided to the terminals. This means that the
base station must be able to distinguish between empty, successful, or a collision in a minislot and provide this
feedback to the terminal stations. Bear in mind that TQ and RQ in practical implementations are simply binary counters.
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Registry
Registry is the Windows database that provides centralized storage of startup, configuration and other information.
The registry stores information about all installed hardware and any software that has been designed expressly
for the Windows operating system. The registry is one of the components that enables Windows to support Plug and
Play and is organized into categories called "registry keys".
The registry replaces many of the Windows 3.x functions previously provided by the AUTOEXEC.BAT, CONFIG.SYS, WIN.INI,
and SYSTEM.INI files, and by individual applications' INI files. These files may still exist in Windows to provide
backward compatibility for any hardware or software needing them. The registry stores its information in two binary
files: SYSTEM.DAT, which maintains up-to-date computer-related data, and USER.DAT, which can maintain multiple
system configurations for different users or purposes.
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Relative URL
The Internet address of a page or other World Wide Web resource relative to the Internet address of the current
page. A relative URL gives the path from the current page to the destination page or resource. A relative URL can
include a protocol. For example, the relative URL doc/sample.htm refers to the page sample.htm in the folder doc,
below the current folder.
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Remote
Remote refers to something that is on a server, as opposed to being on your computer.
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Repeater
Repeater is a device used in a network to strengthen a signal as it is passed along the network cable.
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RFC (Request For Comments)
RFC protocols are outlined in a list of protocols and associated RFC numbers. Although RFCs define protocols not
all RFCs define protocols but may define other requirements for the internet such as RFC 1543 which provides information
about the preparation of RFCs. The following RFCs are very central to the TCP/IP protocol.
RFC 1122
Defines host requirements of the TCP/IP suite of protocols covering the link, network (IP), and transport (TCP,
UDP) layers.
RFC 1123
The companion RFC to 1122 covering requirements for internet hosts at the application layer.
RFC 1812
Defines requirements for internet gateways which are IPv4 routers.
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RIP (Routing Information Protocol)
RIP is a routing protocol in TCP/IP and NetWare that identifies all attached networks as well as the number of
router hops required to reach them.
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RJ-45
RJ-45 is the standard connectors used for unshielded twisted-pair cable.
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ROM (Read-Only Memory)
ROM is a type of data storage device which is manufactured with fixed contents. The term is most often applied
to semiconductor integrated circuit memories. ROM is inherently non -volatile storage - it retains its contents
even when the power is switched off, in contrast to RAM. It is used in part for storage of the lowest level bootstrap
software (firmware) in a computer.
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Router
Router is a computer system that stores and forwards data packets by way of network addresses between Local
Area Networks (LANs) or Wide Area Networks (WANs). Router is a device that routes information between interconnected
networks. It can select the best path to route a message, as well as translate information from one network to
another. It is similar to a superintelligent bridge. So router is a device that forwards traffic between networks.
Forwarding decisions are made based on network layer information and routing tables, often constructed by routing
protocols.
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Row
In a table, a horizontal collection of cells.
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RS-232 Connector
RS-232 is an EIA interface standard between DTE and DCE that uses serial binary data interchange. It's the
industry's most common interface standard. RS-232 abbreviation is from recommended standard-232C, a standard interface
approved by the Electronic Industries Alliance (EIA) for connecting serial devices. In 1987, the EIA released a
new version of the standard and changed the name to EIA-232-D. And in 1991, the EIA teamed up with Telecommunications
Industry association (TIA) and issued a new version of the standard called EIA/TIA-232-E.
Many people, however, still refer to the standard as RS-232C,
or just RS-232. Almost all modems conform to the EIA-232 standard and most personal computers have an EIA-232
port for connecting a modem or other device. In addition to modems, many display screens, mice, and serial printers
are designed to connect to an EIA-232 port.
In EIA-232 parlance, the device that connects to the interface is called a Data Communications Equipment (DCE)
and the device to which it connects (e.g., the computer) is called a Data Terminal Equipment (DTE). |
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The EIA-232 standard supports two types of connectors -- a 25-pin D-type connector (DB-25) and a 9-pin D-type connector
(DB-9). The type of serial communications used by PCs requires only 9 pins so either type of connector will work
equally well.
Although EIA-232 is still the most common standard for serial communication, the EIA has defined successors to
EIA-232 called RS-422 and RS-423. The new standards are backward compatible so that RS-232 devices can connect
to an RS-422 port. Other EIA RS-based standards are as follows.
RS-422, RS-423
EIA interface standards operating with RS-449 that specify electrical characteristics for balanced circuits and
extend transmission speeds and distances beyond RS-232. RS-422 is a balanced-voltage system with high noise immunity;
RS-423 is the unbalanced version.
RS-449
An EIA general-purpose 37-pin and 9-pin interface for DTE and DCE.
RS-485
A balanced interface similar to RS-422 but using tristate drivers for multidrop applications.
RS-530
Similar to RS-449 because it describes a mechanical connector, RS-530 uses a DB25 connector and supports RS-422,
RS-423, RS-485, and V.35 electrical interfaces.
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RTF (Rich Text Format)
RTF is a method of encoding text formatting and document structure using the ASCII character set. By convention,
RTF files have an .rtf filename extension. You can open RTF files in the FrontPage Editor and have them
converted to HTML.
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