Promise Technology 66 Pro - Manual (Page 151)

SuperTrak66™ User's Manual Appendix G
G-2
cache A method of enhancing disk system performance by reducing and
advancing physical drive accesses in an intelligent manner, by
temporarily storing disk data in local RAM. Subsequent access to
cached data is then fetched from RAM which is much faster than
accessing the physical media. Using cache memory, systems can
provide read ahead caching where more data is brought into cache
memory than was requested by the O/S during a particular access.
Read ahead caching anticipates the next read request by the O/S to
increase data read response when the request “hits” the advanced
cache. The same principle is applied with write back cache, the
practice of holding disk write requests in cache memory until a flush is
performed. This effectively combines multiple disk I/Os into a single
operation which may otherwise have been fragmented by the O/S.
channel Refers to a specific channel connection on the SuperTrak66 controller
card. Each cable connected to the controller represents a single
channel.
CHS Cylinder Head Sector: An older method of defining the geometry and
accessing the hardware of media devices such as hard drives. A drive
which has multiple platters is divided up into cylinders which are in
turn divided by heads. Each cylinder/head pair has a sector address
up to the SPT value. Today, this method is used more for backward-
compatibility since LBA is now the prevailing addressing method.
DDM Device Driver Module: A software component of IxWorks. DDM
includes both HDM and ISM, and (potentially) other types of modules.
dirty A term used loosely to describe blocks of drive data in cache memory
which require a flush.
DMA Direct Memory Access: DMA is a system bus device which has its
own logic for addressing a piece of memory in the system without the
use of a CPU to move data. This allows I/O devices such as hard drive
controllers to push data to/from memory without burdening the system
CPU to perform the data transfer to the drive through a mechanism
such as PIO.
EDO Extended Data Out RAM: A type of RAM which has a larger internal
working buffer, boosting performance under normal use.