In the case of a RAID-1 array, one drive must be copied to the other. In the case of RAID-5 arrays, the parity information must be generated. Burst - A term used to describe data words which are transmitted as a single group across a bus without interruption by another device. Bus Mastering - A method of data transfer which allows data to be moved between a peripheral controller and system memory without interaction with the host CPU or a third party DMA controller. A cache management algorithm monitors the data access patterns and selects which data from the slower device is to be kept in the cache for quick access.
Caches are normally transparent or hidden from the accessing device.
Degraded Mode - The mode of operation of a Redundant Array in which it can continue to be accessed after a component drive has failed. For read accesses, data is synthesized from the remaining good drives in the array. For write accesses, data is stored on the remaining good drives in such a way that it can be restored to the failed drive once it is replaced. SCSI devices include peripherals such as disk and tape drives, optical devices, scanners, printers, and host adapters. Differential - An electrical signal protocol which transmits information through a current loop rather than by changes in voltage, thereby reducing the susceptibility to electrical interference.