R/2
SAP's mainframe enterprise management suite, the precursor to R/3.

R/3
SAP's integrated enterprise resource planning (ERP) system for client/server and distributed open systems. It was ported (with enhancements) from R/2. See ERP.

RA (registration authority)
An optional component in a public-key infrastructure (PKI) security implementation. The RA proves an entity's identity before passing its credentials to the certification authority for certificate creation. See PKI and certification authority.

RACF (Resource Access Control Facility)
A security facility for IBM mainframe environments. RACF originated as a feature of the Multiple Virtual Storage (MVS) operating system in 1976 and, more recently, has been incorporated into IBM's OS/390 and z/OS environments. See MVS, OS/390 and z/OS.

rack
A framework or structure that holds computer servers or networking equipment, usually by means of shelves or mounting plates. The height of computer equipment is expressed in rack units (U), which equal the distance between shelf increments in a standard rack (see rack unit).

rack unit (U)
A standard increment used to express the height of a piece of rack-mounted computer or networking equipment, abbreviated as "U" and equal to 1.75 inches. For example, a server with a height of 4U takes up seven inches of vertical rack space. The most common dimensions for an industry-standard rack are 42U (73.5 inches) high and 19 inches wide.

RAD (rapid application development)
An application development approach that includes small teams (typically two to six people, but never more than 10) using joint application development (JAD) and iterative-prototyping techniques to construct interactive systems of low to medium complexity within a time frame of 60 to 120 days. See JAD.

radio channel
A radio frequency (RF) band allocated to a service provider or transmitter. See RF.

radio communications
Communications using electromagnetic frequencies in the approximate range between 20 kilohertz and 3 gigahertz.

RADIUS (Remote Authentication Dial-In User Service)
A security protocol used to transport passwords between the access device and the authentication server.

RAID (redundant array of independent disks)
A method of mirroring or striping data on clusters of low-end disk drives; data is copied onto multiple drives for faster throughput, error correction, fault tolerance and improved mean time between failures. With the exception of RAID 0, all RAID levels provide automated recovery of data in the event of a disk failure. The RAID levels and their key features are:

RAM (random-access memory)
A computer's primary memory, which that can be overwritten with new information. The "random access" part of the name refers to the fact that information bits can be retrieved from RAM in any order.

RAMAC (Random Access Method of Accounting and Control)
A line of IBM disk storage technology. When it was introduced in 1957, RAMAC was the world's first computer disk storage system.

random access
A storage or memory device that allows information or blocks of information to be read in any order (for example, a disk or solid-state memory chip).

RAS (reliability, availability and serviceability)
A reference to a product's quality, availability of optional features, and ease of diagnosis and repair.

RAS (remote-access server)
A server that facilitates network connections to an enterprise local-area or wide-area network from users remotely accessing the network over cable or telephone lines using a modem. The server uses various protocols to authenticate and connect remote users. It may have multiple network interfaces and include integrated bridging or routing. Remote access servers are customer premises equipment, although they can be bought and used by small Internet service providers.

raster
Originally a German word for the screen used in photoengraving; now, the array of scan lines used to cover a planar area to read or depict image information on that area (for example, in a printed image or on a video screen).

RBOC (regional Bell operating company)
A local or regional telephone company in one of seven regions of the United States formed by the divestiture of AT&T. Also known as Bell operating company (see BOC) or, colloquially, as a "baby Bell."

RC2 (Rivest Cipher 2)
One of a family of proprietary ciphers developed by Ronald Rivest of RSA Security. RC2 is a secret-key block cipher — that is, it encrypts data one fixed-size block at a time — for bulk encryption. See block cipher, RSA and secret key.

RC4 (Rivest Cipher 4)
A secret-key cipher developed in 1987 by Ronald Rivest or RSA Security. Unlike Rivest Cipher 2 (RC2) and Rivest Cipher 5 (RC5), RC4 is stream cipher —it encrypts data as a sequence of bits, one bit at a time. See RC2, RC5 and stream cipher.

RC5 (Rivest Cipher 5)
The latest in a family of secret-key cryptographic methods developed by Ronald Rivest of RSA Security. RC5 is a block cipher; it is more secure than RC4, but slower. See block cipher, secret key and RC4.

RCM (reliability-centered maintenance)
A formalized approach to the maintenance of physical assets. RCM systematically applies scheduled inspections, preventive maintenance and other techniques to increase the efficiency and effectiveness of equipment maintenance programs.

R&D (research and development)
A descriptive term for the function, organization or budget allocation devoted to researching and developing new products or technologies.

Rdb
A database management system from Hewlett-Packard (originally from Digital Equipment, and later Compaq Computer). Rdb is integrated with the other Virtual Address Extension (VAX) Information Architecture products, and is designed to provide true multiplatform, distributed-database capabilities. See VAX.

RDBMS (relational database management system)
A database management system (DBMS) that incorporates the relational data model, normally including a Structured Query Language (SQL) application programming interface. It is a DBMS in which the database is organized and accessed according to the relationships between data items. In a relational database, relationships between data items are expressed by means of tables. Interdependencies among these tables are expressed by data values rather than by pointers. This allows a high degree of data independence. See DBMS and SQL.

RDF (Resource Description Framework)
A proposed World Wide Web Consortium (W3C) standard for metadata descriptions. See W3C and metadata.

RDM (Remote Deployment Manager)
An IBM tool (formerly called LANClient Control Manager, or "LCCM") that allows systems administrators to remotely configure and deploy operating systems and applications on IBM systems. RDM remotely identifies systems and collects data, such as system memory, hard disk capacity and BIOS information.

RDP (Remote Desktop Protocol)
Microsoft's protocol for remote presentation. See remote presentation.

RDRAM (Rambus Dynamic Random-Access Memory)
A memory chip design, from Rambus Inc. (Los Altos, California), that speeds up computer systems by accelerating the exchange of data between memory and surrounding logic chips.

real-time clock
A hardware clock system powered by battery when the PC is switched off. This clock is paced by a quartz crystal and operates in a similar fashion to a digital watch, maintaining information for the year, month, day, hour, minute and second.

recording density
The number of bits that can be written on a specific area of magnetic media, generally measured in bits per inch.

record management
The systematic organization and managed storage of diverse information sources through the end of their life cycles. Record management can be viewed as a subset of integrated document management (IDM) and is one of the five most important IDM library service functions. The others are check-in/check-out; version control; document-level security and attributes; and full-text-index search and retrieval. See IDM.

red book
Informal term for the Comite Consultatif International Telegraphique et Telephonique (CCITT) standards approved in 1984. See CCITT and International Telecommunication Union.

1. Portion of the total information contained in a message that can be eliminated without loss of essential information.

2. Provision of duplicate, backup equipment or links that immediately take over the function of equipment or transmission lines that fail.

referential integrity
The underlying rules defining the semantic interdependencies among items in a database. The goal is to define those items declaratively (that is, as business-oriented assertions) rather than through procedural logic.

refresh rate
The speed at which an image is "painted" onto a monitor screen.

relationship management
The function in an enterprise or external service provider (ESP) that acts as an organizational liaison — for example, between an enterprise's IS department and its business units, or between an ESP and the customer enterprise.

relay
An electronically operated device that causes abrupt changes in an electrical circuit, such as breaking the circuit, changing the circuit connection or varying the circuit characteristics.

remote access
The ability to connect to a network from a distant location. Generally, this requires a computer, a modem and remote-access software to allow the computer to connect to the network over a public communications network (such as a phone or cable network).

remote-access VPN
A virtual private network (VPN) that creates encrypted tunnels between remote users and a campus network. See VPN.

remote console
A console facility that enables a remote operator to perform normal operational tasks, including storage backup, on a running system.

remote control
Control of a computer or its applications from another computer or terminal in a remote location. Historically, this concept described certain legacy mainframe applications (for example, those accessed over an IBM 3270 terminal). More recently, the term is often applied to software that allows a PC to have complete control over another PC at a different site.

remote data management
A form of client/server computing in which the database management system or file management system executes on a different computer than the rest of the application logic. See client/server.

remote presentation
A form of client/server computing in which the presentation executes on a different computer than the rest of the application logic and data management. See client/server.

remote system monitoring
Software facilities that enable system operation to be monitored from a remote site, and that notify remote operators of system conditions that fall outside of specified parameters.

repeater
A network device that extends the range of a signal by amplifying, re-timing it and re-transmitting it.

repository
A facility for storing descriptions, definitions and other information on data or systems in an enterprise. A system repository would include configuration definitions, tuning parameters and performance goals, while an application repository would include data definitions.

resolution
The measure of the capability of a visual system (such as a video, fax or printing system) to reproduce image detail.

resource exchange
A Web site that enables enterprises in need of specific talent (for example, database administration) to select from many suppliers. Resource exchanges focus on putting the buyer in control. They usually aggregate content from multiple suppliers of staff and services, and provide decision support tools to help buyers make informed decisions.

response time
The time period between a system user's completion of an inquiry and the receipt of a response. Response time includes the time taken to transmit the inquiry, process it by the computer, and transmit the response back to the terminal. Response time is frequently used as a measure of the performance of an interactive system.

reuse
An application development methodology that catalogs and makes available application components so that they may be incorporated into other applications.

REXX (Restructured Extended Executor)
A structured, interpretive language used to create operator-level command streams to manage and link applications in IBM mainframe environments.

RF (radio frequency)
The electromagnetic frequency range used for radio communication, i.e., frequencies between approximately 20 kilohertz and 3 gigahertz.

RFC (request for comment)
A document submitted for comment and put through a review process under the auspices of the Internet Engineering Task Force (IETF). When accepted, it has the weight of a standard in the Internet community. Each RFC is given a tracking number. For example, RFC 822 describes the address format and data definitions for addressing electronic messages over the Internet, while RFC 1490 is a standard specification for encapsulating multiple protocols over a wide-area frame relay network.

RFI (request for information)
Notification of an intended acquisition sent to potential suppliers to determine interest and gather general descriptive product materials (but not prices). The RFI is generally used to determine to which vendors to send a formal request for proposal (RFP). See RFP.

RFID (radio frequency identification)
An analog-to-digital conversion technology that uses radio frequency (RF) waves to transfer data between a movable item and a reader for identification, tracking or location purposes. It does not require physical contact or a line of sight between the reader or scanner and the tagged item. This is one advantage over a bar code system, while another is that RFID tags can be read over a longer range — 100 feet or more. A typical RFID system has three components:

RFP (request for proposal)
An invitation for vendors to bid on supplying goods and services. It defines specific functions to be provided, the installed computing environment and any project work in progress.

RFQ (request for quotation)
Solicitation for pricing for a specific software product, service or system.

RHC (regional holding company)
A company created from the AT&T divestiture (originally, there were seven; now there are five). Each RHC acts as a holding company within a region of the United States for one or more of the divested Bell operating companies, as well as for their unregulated subsidiaries. The RHCs are: Ameritech, Verizon (formerly Bell Atlantic), BellSouth, SBC Communications and US West.

RIM (Reference Information Model)
A comprehensive, object-oriented information model for clinical healthcare. RIM serves as a semantic point of reference for all Health Level Seven (HL7) standards development efforts. See HL7.

RIM (Research in Motion)
A vendor of wireless communication products based in Waterloo, Ontario. Its products include the popular BlackBerry handheld device (see BlackBerry).

ring topology
A network topology in which each node is connected to two adjacent nodes to form a continuous-ring configuration.

RIP (raster image processor)
A device that converts computer graphics into a raster image — a grid of small dots — from which the printing device will re-create them on paper.

RIP (Routing Information Protocol)
An internal router protocol used for informing network computers of changes in configuration. See router.

RIS (radiology information system)
A system that supports the information-processing and business requirements of radiology departments and free-standing image centers.

RISC (reduced instruction set computer)
A processor architecture that shifts the analytical process of a computational task from the runtime execution phase to the preparatory "compile time" phase. By using less hardware or logic, the system can operate at higher speeds. RISC cuts down on the number and complexity of instructions, so that each instruction can be accessed and executed more quickly and less semiconductor "real estate" is required to process them. The result is that a more powerful microprocessor can be produced with RISC than with complex instruction set computer (CISC) architectures. See CISC.

risk transfer
The ability to make another party liable for the risk involved in a service function. A key component of the value of hiring an external service provider (ESP) is the ability to transfer risk. See ESP.

RJ11 (Registered Jack 11)
The physical specification for the four-wire jack commonly used in U.S. telephone systems.

RJ45 (Registered Jack 45)
A type of eight-wire connector commonly used in local-area networks.

Rlogin (Remote Login)
A protocol for communication between Berkeley Software Distribution (BSD) Unix systems attached to the same local-area network. It was developed when Telnet did not support all the services that users required. See BSD and Telnet.

RMI (Remote Method Invocation)
A Java technology that allows one application process to invoke services existing in another, remote application environment. See Java.

RMON (Remote Monitoring)
A specification that builds on the functionality of Simple Network Management Protocol (SNMP) by extending the definition of the SNMP management information base (MIB) to enable network managers to monitor subnetwork devices via the MIB. RMON also enables the local collection of device data, thereby helping network administrators address the bandwidth constraints imposed by SNMP's device-polling design. See SNMP and MIB.

RNIF (RosettaNet Implementation Framework)
A framework that provides generic specifications for sending Extensible Markup Language (XML) messages securely over the Internet using Hypertext Transport Protocol (HTTP) or Secure HTTP. RNIF is defined by the RosettaNet consortium. See XML and RosettaNet.

roaming
A search for available cellular-network carriers performed by mobile phone.

ROE (return on equity)
A measure of a company's financial performance. Expressed as a percentage, ROE is calculated by dividing net income by the value of the stockholders' equity.

ROI (return on investment)
Financial gain expressed as a percentage of funds invested to generate that gain.

ROLAP (relational online analytical processing)
A type of online analytical processing (OLAP) that uses relational database management systems (RDBMSs) to store multidimensional data in relational data tables, and new object types that support multidimensional analysis. ROLAP databases have the advantage of scalability and flexibility, but typically lack the query performance of true multidimensional OLAP systems. See RDBMS, OLAP and MDDB (multidimensional database).

rollback
The return of a system to a previous state. Typically, it is enabled by maintaining "before" and "after" images of an altered system in a log file so that, if the system fails, the unsuccessful updates can be backed out or "rolled back."

ROM (read-only memory)
Data stored in computer memory that can be accessed and read by the user, but not modified. ROM is often permanent, and stores system control software.

RossettaNet
A consortium that provides application standards based on Extensible Markup Language (XML) to align supply chain business processes. Its standards, which include the RosettaNet Implementation Framework (RNIF), are widely respected for their approach to standardizing messages for multistep processes. See RNIF and XML.

router
A class of network controller that determines the best routing for data transmission between a transmitter (sender) and a receiver. Routers are typically software-controlled and can be programmed to provide the least expensive, fastest or least busy of available routes. Routers operate at Layer 3 of the Open Systems Interconnection (OSI) network model. See OSI.

routing table
A table used by a network switch or router to determine the preferred path for a message to take to reach a given destination on the network.

RPC (remote procedure call)
A mechanism that extends the notion of local application procedure calls to a distributed computing environment. RPCs enable applications to be distributed among multiple systems in a way that is highly transparent to the application-level code.

RPG (Report Program Generator)
An IBM-proprietary procedural-programming language, most commonly used on the AS/400 family of computers (now known as the eServer iSeries).

RPO (recovery point objective)
A term used in disaster recovery and business continuity planning. The RPO defines what constitutes an acceptable loss of data — specifically, the required timeliness of the data that can be recovered using backups, journals or transaction logs.

RS-232
An Electronic Industries Alliance (EIA) physical interface specification for serial data connections. Originally introduced in 1962, RS-232 (sometimes presented as "RS232") is the most commonly employed interface between computers and modems. As the EIA and its telecom subgroup, the Telecommunications Industry Association (TIA), have released updated versions over the years, the formal name of the specification has changed — for example, to "EIA-232-D," "EIA/TIA-232-E" and, most recently, "TIA/EIA-232-F." Regardless of the version, however, the specification is still commonly referred to by the original "RS-232" appelation.

RS/6000 (RISC System/6000)
An IBM technical workstation introduced in 1990. It is based on reduced instruction set computer (RISC) architecture and runs the Unix-based Advanced Interactive Executive (AIX) operating system. See RISC, Unix and AIX.

RSA (Rivest-Shamir-Adelman)
A public-key algorithm invented in 1997 by Ron Rivest, Adi Shamir and Leonard Adleman. The encryption software company RSA Security, Headquartered in Bedford, Massachusetts, once owned the rights the algorithm, which has since entered the public domain. See public-key encryption.

RSVP (Resource Reservation Protocol)
A transport-layer protocol used to improve network quality of service (QOS) by reserving the resources (such as bandwidth and buffer space) that applications require. Developed by the Internet Engineering Task Force (IETF), RSVP relies on end devices to request their priority so that resources can be reserved for flows to facilitate the requested QOS. Each router along the path to the end device attempts to honor the RSVP request by maintaining connection state information. If this cannot be honored, service is denied and packets are dropped. See QOS and IETF.

RTCP (Real-Time Transport Control Protocol)
An Internet Engineering Task Force (IETF) protocol that works in conjunctions with Real-Time Transport Protocol (RTP) to provide services for the transport of real-time data, such as audio and video. RTCP provides feedback from receiver to sender on current network performance, helping to optimize coding speeds to varying network conditions. See RTP, OSI and IETF.

RTE (real-time enterprise)
An enterprise that achieves competitive advantage by using up-to-date information to progressively remove delays in the management and execution of its critical business processes.

RTF (Rich Text Format)
A file format that encodes documents so their messages include boldface, italics and other limited text stylings across platforms and applications. Differences exist between implementations by Lotus and Microsoft.

RTO (recovery time objective)
Often called the "recovery window," the RTO defines how quickly information systems, services and processes must be operational for disaster recovery purposes.

RTOS (real-time operating system)
An operating system that responds to an external event within a short and predictable time frame. Unlike a batch or time-sharing operating system, a real-time operating system provides services or control to independent, ongoing physical processes. It typically has interrupt capabilities (so that a less important task can be put aside) and a priority-scheduling management scheme.

RTP (Real-Time Transport Protocol)
An Internet Engineering Task Force (IETF) protocol that defines a mechanism for providing network transport functions suitable for applications transmitting real-time data, such as audio and video. RTP provides end-to-end delivery services, including payload type identification, sequence numbering and time stamping, which can be used by end systems to properly pace audio and video playback. See IETF.

rt-VBR (real-time variable bit rate)
An asynchronous transfer mode (ATM) service category, defined by the ATM Forum, that provides service guarantees for traffic with timing constraints (usually for compressed voice or video).

R-UIM (removable user identity module)
A smart card —similar to the Global System for Mobile Communications (GSM) subscriber identity module (SIM) — that is designed to be used in mobile phones based on code division multiple access (CDMA). It allows roaming across CDMA and GSM networks. The specifications for R-UIM were introduced by the CDMA Development Group and the 3rd Generation Partnership Project (3GPP), and were approved for publication by the Telecommunications Industry Association in 2000. R-UIMs will be implemented first on handset shipments in China and subsequently in other countries where both GSM and CDMA networks are prevalent. See SIM, smart card, CDMA, GSM and 3GPP.

rule-based technology
Technology that applies a collection of rules to captured information to deduce or infer new information, using an interface engine. Applications include medical diagnosis, insurance underwriting, regulatory compliance and customer service.

runtime
Literally, the period during which an application or system is running. Traditionally, it refers to the period during which a program is executing, after it has been compiled and loaded. Today, the term is often used in the context of middleware and component-based technologies (such as Java and .NET) that invoke procedures or create application execution environments during the runtime period. See Java and .NET.

RVA (RAMAC Virtual Array)
An IBM disk storage system.