NonStop S-Series Hardware Installation and FastPath Guide (G06.26+)

Glossary
HP NonStop S-Series Hardware Installation and FastPath Guide—529876-001
Glossary-25
direct jump area
direct jump area. One of sixteen 256-megabyte portions of the 4-gigabyte virtual address
space. A RISC jump instruction has the ability to jump directly to any location within its
own direct jump area without having to use a far jump table.
direct memory access (DMA). A technique for transferring data from main memory to a
device without passing it through the CPU.
directory. A type of Open System Services (OSS) special file that contains directory entries,
which associate names with files. No two directory entries in the same directory have
the same name.
directory entry. In the Open System Services (OSS) file system, an object that associates
a filename with a file. Several directory entries can associate names with the same file.
See also link.
directory loop. In the Open System Services (OSS) file system, an error condition in which
a directory is identified as its own parent directory.
directory special file. See directory.
directory stream. In the Open System Services (OSS) file system, an object with an
opaque data type. A process can sequentially read directory entries from a directory
stream.
directory tree. A hierarchy of directories. In the Open System Services (OSS) environment,
directories are connected to each other in a branching hierarchical fashion such that
only one path exists between any two directories (if no backtracking occurs).
disconnecting means. A device, group of devices, or other means by which the conductors
of a circuit can be disconnected from their source of supply.
discovery. For the OSM and TSM client software, the process of identifying the resources
that exist on an HP NonStop™ server. See also incremental discovery and initial
discovery.
disk bootstrap. A software entity residing on disk that is used to load the HP NonStop™
operating system image (OSIMAGE) into memory during a system load. A disk that
contains the disk bootstrap is referred to as a bootable disk. The disk bootstrap is
placed on the disk either as part of a tape load or as a result of the SCF CONTROL
DISK, REPLACEBOOT command.
disk cache. A temporary storage buffer into which data is read, retained, and perhaps
updated before being written to disk, for more efficient processing.
disk drive. A device that stores and accesses data on a magnetic disk. Random access to
addressable locations on a magnetic disk is provided by magnetic read/write heads.
See also volume
.