Abbreviated VAN. A communications network, such as Telenet or Tymnet, that offers services in addition to communications connections and data transmission. Types of value-added services include message routing, resource management, and conversion facilities for computers communicating at different speeds or using different codes or protocols.
A coating for optical-disc platters that permits the raising of small bumps on the surface instead of the pits used in standard CD-ROM discs for recording data. Bumps, unlike pits, can be flattened out to make an optical disc erasable and thus rewritable.
Commonly called a RAM disk. Random access memory (RAM) used as a disk drive. Because the computer does not need to wait for the hardware to respond, reading and writing to such a “disk” can vastly improve performance. However, because a virtual disk exists only in memory, its contents must be copied to a physical disk or the data will be lost. The exception is a virtual disk on battery-backed RAM, which is RAM that has its own battery; when the power to the computer is turned off, that battery ensures that the contents of RAM are left intact. Ultralight laptops often use battery-backed RAM as a virtual disk because such storage consumes less power than a hard disk.
Also called disk memory. A technique that allows an application to see the system as providing a large uniform primary memory, which in reality is smaller, more fragmented, and/or partially simulated by secondary storage such as a hard disk. Applications access memory through virtual addresses, which are translated (mapped) by special hardware onto physical addresses. Paging and segmentation are two common implementations of virtual memory.
the derived SI unit of electric potential; the potential difference between two points on a conductor.
Acronym for vertical redundancy check. An error-checking method used to check the accuracy of transmitted data. VRC generates an extra bit (party bit) for each character transmitted. The party bit determines whether the character (byte) contains an odd (for odd parity) or an even (for even parity) number of 1 bits. If its value does not correspond with the type of parity being used, the character is assumed to be incorrect.