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• Radio Frequency Identification:
  RFID first appeared in tracking and access applications during the 1980s. It is a method of remotely storing and retrieving data using devices called RFID tags/transponders and is coming into increasing use as an alternative to the bar code.
   

• RAID:
  Short for Redundant Array of Independent (or Inexpensive) Disks, a category of disk drives that employ two or more drives in combination for fault tolerance and performance. RAID disk drives are used frequently on servers but aren't generally necessary for personal computers.
  
  There are number of different RAID levels. The three most common are 0, 3, and 5:
  
  Level 0: Provides data striping (spreading out blocks of each file across multiple disks) but no redundancy. This improves performance but does not deliver fault tolerance.
  
  Level 1: Provides disk mirroring.
  
  Level 3: Same as Level 0, but also reserves one dedicated disk for error correction data. It provides good performance and some level of fault tolerance.
  
  Level 5: Provides data striping at the byte level and also stripe error correction information. This results in excellent performance and good fault tolerance.
   

• RAM:
  (Random Access Memory) A configuration of memory cells that hold data for processing by a computer's central processing unit, or CPU; (see also memory). The term random derives from the fact that the CPU can retrieve data from any individual location, or address, within RAM.
   

• Ranging:
  The process of automatically adjusting transmit levels and time offsets of individual modems, in order to make sure the bursts coming from different modems line up in the right timeslots and are received at the same power level at the CMTS.
   

• RAS:
  Short for Remote Access Services, a feature built into Windows NT that enables users to log into an NT-based LAN using a modem, X.25 connection or WAN link. RAS works with several major network protocols, including TCP/IP, IPX, and Netbeui.
  
  To use RAS from a remote node, you need a RAS client program, which is built into most versions of Windows, or any PPP client software. For example, most remote control programs work with RAS.
   

• RDRAM:
  Rambus DRAM technology is a system-wide, chip-to-chip interface design that allows data to pass through a simplified bus. Rambus uses a unique RSL (Rambus Signaling Logic) technology. Rambus is available in two flavors: RDRAM and Concurrent RDRAM. RDRAM is currently in production with Concurrent RDRAM production scheduled for late 1997. The third line extension, Direct RDRAM, is in development stages and scheduled for production in 1999. In late 1996, Rambus agreed to a development and license contract with Intel that will lead to Intel's PC chip sets supporting Rambus memory starting in 1999.
   

• RealAudio: 
  This is a method of playing sounds invented by Rob Glasser that creates a buffer between the supplying server and your computer. The file is played without downloading it completely.
   

• Real Player:
  Developed by RealNetworks, this is a cross-platform multi-media player.
   

• Real Time:
  This is method of processing data the moment it is received. Batch mode is a term used for a mainframe computer dealing with data when it has the time.
   

• Reboot:
  To restart a computer. In DOS, you can reboot by pressing the Alt, Control and Delete keys simultaneously. This is called a warm boot. You can also perform a cold boot by turning the computer off and then on again.
  
  On Macs, you reboot by selecting the "Restart" option from the Special menu.
   

• Redundant:
  Array of Inexpensive (or Interconnected) Disks. A performance enhancing method of storing the same data in different places on multiple hard disks. Unnecessary redundancy can cause problems if one copy of the data is updated and another copy of the data is not. All redundant data can’t be eliminated in most databases because primary keys in one table are repeated in other tables as foreign keys to create links between tables. This type of redundancy is called controlled redundancy.
   

• Refresh:
  Generally, to update something with new data. For example, some Web browsers include a refresh button that updates the currently display Web pages. This feature is also called reload.
  To recharge a device with power or information. For example, dynamic RAM needs to be refreshed thousands of times per second or it will lose the data stored in it.
  
  Similarly, display monitors must be refreshed many times per second. The refresh rate for a monitor is measured in hertz (Hz) and is also called the vertical frequency, vertical scan rate, frame rate or vertical refresh rate. The old standard for monitor refresh rates was 60Hz, but a new standard developed by VESA sets the refresh rate at 75Hz for monitors displaying resolutions of 640x480 or greater. This means that the monitor redraws the display 75 times per second. The faster the refresh rate, the less the monitor flickers.
   

• Refresh Rate:
  Refers to the speed in which an image can be flashed or re-drawn on a monitors screen. The higher the refresh rate, the more unnoticeable the flashing will be to the naked eye. A low refresh rate will make the imagery appear very unsteady or jerky. The typical refresh rate in the United States is 60 hertz (Hz).
   

• Registered Memory:
  This memory uses "registers" which are extra chips designed to delay the flow of data. By delaying the data flow, it allows for better control over communication in systems with heavily loaded memory.
   

• Registry:
  In a Windows operating system, the registry is the database of information that stores all of the setup, user preferences, software and hardware configuration information.
   

• Relational Database:
  A method in which data is stored in multiple tables so that the data can be organized by pre-defined relationships.
   

• Repeater:
  A device that receives weak incoming signals, boosts the signal and then retransmits the signal. Its purpose is to extend the signals distance while keeping adequate signal strength.
   

• Resolution:
  Refers to the sharpness and clarity of an image. The term is most often used to describe monitors, printers, and bit-mapped graphic images. In the case of dot-matrix and laser printers, the resolution indicates the number of dots per inch. For example, a 300-dpi (dots per inch) printer is one that is capable of printing 300 distinct dots in a line 1 inch long. This means it can print 90,000 dots per square inch.
  
  For graphics monitors, the screen resolution signifies the number of dots (pixels) on the entire screen. For example, a 640-by-480 pixel screen is capable of displaying 640 distinct dots on each of 480 lines, or about 300,000 pixels. This translates into different dpi measurements depending on the size of the screen. For example, a 15-inch VGA monitor (640x480) displays about 50 dots per inch.
  
  Printers, monitors, scanners, and other I/O devices are often classified as high resolution, medium resolution, or low resolution. The actual resolution ranges for each of these grades is constantly shifting as the technology improves.
   

• Resource:
  Generally, any item that can be used. Devices such as printers and disk drives are resources, as is memory.
  In many operating systems, including Microsoft Windows and the Macintosh operating system, the term resource refers specifically to data or routines that are available to programs. These are also called system resources.
   

• RFID:
  Radio Frequency identification (ID). Refers to the technology that uses devices attached to objects that transmit data to an RFID receiver. An alternative to bar coding. Advantages include data capacity, read/write capability, and no line-of-sight requirements. 
   

• RIMM:
  Rambus In-Line Memory Module. RIMM is a synchronous dynamic random access memory (RAM) module that is used on newer motherboards. RIMM's are manufactured by Rambus Corporation.
   

• Ripper:
  This refers to a software application capable of transferring digital audio files from a CD to a hard drive.
   

• RISC:
  Reduced Instruction Set Computer. A computer processing architecture that requires fewer instructions to run applications, thus increasing processing speed.
   

• RJ-11:
  Short for Registered Jack-11, a four- or six-wire connector used primarily to connect telephone equipment in the United States. RJ-11 connectors are also used to connect some types of local-area networks (LANs), although RJ-45 connectors are more common.
   

• RJ-45:
  Short for Registered Jack-45, an eight-wire connector used commonly to connect computers onto a local-area networks (LAN), especially Ethernets. RJ-45 connectors look similar to the ubiquitous RJ-11 connectors used for connecting telephone equipment, but they are somewhat wider.
   

• ROM:
  Stands for Read-Only Memory. A semiconductor-based memory system that stores information permanently and does not lose its contents when power is switched off. ROMs are used for firmware, such as the BIOS used in the PC; and in some portable computers, application programs and even the operating system are being stored in ROM.
   

• Rootkit:
  A set of programs used by hackers to gain access to information contained in your operating system and can even mask its presence. The program can also be used to access computers within a network. Usually, the rootkit is written for malicious purposes.
   

• Router:
  A device that connects any number of LANs. Routers use headers and a forwarding table to determine where packets go, and they use ICMP to communicate with each other and configure the best route between any two hosts. Very little filtering of data is done through routers. Routers do not care about the type of data they handle.
   

• Routing Switch:
  A switch that also performs routing operations. Usually a switch operates at layer 2 (the Data Link layer) of the OSI Reference Model while routers operate at layer 3 (the Network layer). Routing switches, however, perform many of the layer 3 functions usually reserved for routers. And because the routing is implemented in hardware rather than software, it is faster. The downside of routing switches is that they are not as powerful or as flexible as full-fledged routers.
  
  Because they perform some layer 3 functions, routing switches are sometimes called layer-3 switches.
   

• RPL:
  Request Parameter List. A VTAM (Virtual Telecommunications Access Method) control block that contains parameters necessary for processing a request (data transfer, connecting or disconnecting a terminal, etc). 
  
  Also, Relocatable Program Library. A data set used to store CICS (Customer Information Control System) application programs, which are fetched (loaded) at execution time.
   

• RSS: (Rich Site Summary) 
  XML format for distributing news headlines on the Web, also known as Really Simple Syndication.  

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