Τεχνικός Υπολογιστών CompTIA A+

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radiation pattern Sometimes called a propagation pattern, the direction(s) a radio frequency is sent or received.

radio A wireless input/output technology that has a longer range than infrared.

radio firmware Low-level software that manages a cell phone’s radio connection to a network. A baseband signal sends updates to both the phone’s operating system and its radio firmware. Without the same updates, the cell phone experiences problems.

RADIUS (Remote Authentication Dial-in User Service) A secure method of authentication using a server.

RAID (redundant array of independent [or inexpensive] disks) Allows writing to multiple hard drives for larger storage areas, better performance, and fault tolerance.

RAID 0 Also called disk striping without parity, a type of RAID that enables data to be alternatively written on two or more hard drives but be seen by the system as one logical drive. RAID level 0 does not protect data if a hard drive fails; it increases only system performance.

RAID 1 Also called disk mirroring or disk duplexing, a type of RAID that protects against hard drive failure. See also disk mirroring and disk duplexing. Requires two drives at a minimum.

RAID 10 A RAID condition in which a mirrored set and a striped set are combined. Takes four hard drives as a minimum.

RAID 5 Describes putting data on three or more hard drives, with one of the three drives used for parity. See also RAID.

RAID not found An error condition that sometimes occurs with a power failure or surge, misconfiguration in BIOS/UEFI, system upgrade, application upgrade, or new application installation.

RAID stops working An error condition that requires using the Windows Disk Management tool to verify the status of the drives used in the RAID.

rainbow table A security attack method used to obtain a password in a shorter amount of time because the attacker has a table that contains previously discovered hash values.

RAM (random-access memory) A volatile type of memory that loses its data when power to the computer is shut off.

RAM limitation The maximum amount of memory that an operating system can recognize. Even if a system has more installed, the operating system will not be able to use that extra memory.

random-access time A performance comparison measurement; it is the amount of time a drive requires to find the appropriate place on the disc and retrieve information.

ransomware A security situation in which a hacker has restricted access to a device until the user is pressured to pay money to regain access.

rapid elasticity The ability for a provider to expand software and hardware quickly in response to a customer’s needs.

RAS (remote access service) Software that allows one network device to connect to another network device.

RAW volume A part of a hard drive that has been set aside as a volume but has never been high-level formatted and does not contain a specific type of file system.

RCA A type of connector used with coaxial cable.

rd (Remove Directory) A Windows command used to remove a directory (folder).

RDP (Remote Desktop Protocol) A Microsoft protocol used for accessing and controlling networked computers and mobile devices. RDP uses port 3389.

re-image A process of putting a new image (operating system, applications, and settings) on a corporate computer.

read/write failure An error condition that indicates a hard drive has a defective area.

read/write head The part of a floppy or hard drive that electronically writes binary data on disks.

ReadyBoost A utility that can speed up the Windows boot process by caching some startup files to a 256 MB+ flash drive, SD card, or CF card.

reboot A restart of an operating system, also known as a warm start.

rebuild a Windows profile If a message appears that the user profile cannot be loaded, make a copy of the user profile folder, rename the registry key, and have the user log in again.

recover OS The process of repairing, replacing, uninstalling, and reinstalling the operating system.

recovery disc A disc used to boot a system when you don’t have an original operating system disc and then restore the computer from a previously saved system image. Sometimes called a system repair disc.

recovery partition An optional partition provided by some vendors that contains the operating system, files, and applications installed on the system when purchased.

Recycle Bin A location in Windows-based operating systems in which user-deleted files and folders are held. This data is not discarded from the computer. The user must empty the Recycle Bin to erase the data completely.

refresh (installation method) A Windows 8/8.1 tool that reinstalls the operating system but keeps user data and settings. Windows 10 uses Reset This PC for this purpose.

refresh (process) A rewrite of the information inside memory chips.

refresh rate Measured in hertz (Hz) or milliseconds (ms), the amount of time it takes a screen to be drawn in one second. In LCDs, it is also called temporal resolution. LCD refresh rates are traditionally 60 Hz.

Refresh Your PC A Windows 8/8.1 tool that reinstalls the operating system but keeps user data and settings. Windows 10 uses Reset This PC for this purpose.

ReFS (Resilient File System) The Microsoft replacement file system for NTFS.

regedit A Windows utility that can modify and back up the registry.

regedt32 One of two Windows registry editors. See also registry and regedit.

region code A setting on a DVD or Blu-ray drive or disc that specifies a geographic region. The drive’s region code must match the disc’s region code.

registered memory Memory modules that have extra chips (registers) near the bottom of the module that delay all data transfers by one clock tick to ensure accuracy.

registry A central Windows database file that holds hardware and software configuration information.

regsvr32.exe A command used to register .dll files in the Windows registry.

regulatory and compliance policy A policy that is specific to an industry such as health care or manufacturing.

relational operator An operator that compares one side of an expression to another and is used in scripts.

Reliability Monitor A tool that provides a visual graph in Windows Vista or 7 of how stable the system is and shows details on events that might have affected system reliability.

reload OS A repair option that installs a new copy of the operating system when other repair options haven’t been successful in fixing the problem.

Remote Assistance A Windows tool used to remotely access a Windows device. The remote computer displays a prompt requesting permission for remote access. Contrast with Remote Desktop, which does not request permission.

remote backup An option on a mobile device to allow the device or specific data like personal contacts, videos, pictures, and/or music to be backed up to remote storage.

Remote Desktop Connection A Windows tool used to remotely access a Windows-based device that does not require someone to be at that computer and does not prompt for permission. Contrast with Remote Assistance, which does prompt for permission.

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