Instruction Manual

158 Glossary
Battery Backup Unit (BBU)
The battery backup unit protects the integrity of the cached data on the
controller by providing backup power if there is a complete AC power failure or
a brief power outage.
BIOS
Basic Input/Output System. Your system's BIOS contains programs stored on a
flash memory chip. The BIOS controls the following: communications between
the microprocessor and peripheral devices, such as the keyboard and the video
adapter, and miscellaneous functions, such as system messages.
BIOS Configuration Utility
The BIOS Configuration Utility, also known as <Ctrl><R>, configures and
maintains RAID disk groups and virtual disks, and manages the RAID system.
The operation of this utility is independent because the utility resides in the
controller BIOS.
C
Cache
A fast memory that holds recently accessed data. Using cache, speeds
subsequent access to the same data. It is most often applied to processor-
memory access but also can be used to store a copy of data accessible over a
network. When data is read from or written to main memory, a copy is also saved
in cache memory with the associated main memory address. The cache memory
software monitors the addresses of subsequent reads to see if the required data
is already stored in cache memory. If it is already in cache memory (a cache hit),
it is read from cache memory immediately and the main memory read is aborted
(or not started). If the data is not cached (a cache miss), it is fetched from main
memory and saved in cache memory.
Caching
The process of utilizing a high speed memory buffer, referred to as a cache , in
order to speed up the overall read or write performance. This cache can be
accessed at a higher speed than a disk subsystem. To improve read performance,
the cache usually contains the most recently accessed data, as well as data from
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