NonStop System Glossary

segment
In general, a contiguous sequence of logically related pages of virtual memory. The pages of the
segment are individually swapped in and out of physical memory as needed. Within a loadable
object file, one of the portions of the file that is mapped as one unit into virtual memory as the file
is loaded. See also code segment and data segment.
selectable segment
A type of logical segment formerly known as an extended data segment. The data area for a
selectable segment always begins with relative segment 4, and this area can be dynamically
switched among several selectable segments by calls to the Guardian SEGMENT_USE_ procedure.
The effect is similar to a rapid overlaying of one large data area. See also logical segment and
flat segment.
SEM
See ServerNet extender module (SEM).
semaphore
A mechanism used to provide multiple processes with access to a shared data object.
semi-globalized
An import control characteristic of a loadfile that allows the loadfile first to obtain symbols from its
own definitions and then to obtain others as for a globalized loadfile. See also searchList.
sensitive command
A Subsystem Control Facility (SCF) command that can be issued only by a user with super-group
access, by the owner of the subsystem, or by a member of the group of the owner of the subsystem.
The owner of a subsystem is the user who started that subsystem (or any user whose application
ID is the same as the server ID—the result of a PROGID option that requires super-group access).
Contrast with nonsensitive command.
SEP table
See system entry-point (SEP) table.
separately derived power source
A facility wiring system where power is derived from a generator, transformer, or converter windings
and there is no direct electrical connection, including a solidly connected grounded circuit conductor
(neutral), to supply conductors originating in other facility wiring systems. Types of separately
derived power sources include standby power generator, uninterruptible power supply (UPS),
isolation transformer, and computer-room power center (CRPC).
Serial Attached SCSI (SAS)
A data transfer technology designed to move data to and from computer storage devices such as
hard drives and tape drives. It is a point-to-point serial protocol that replaces the parallel SCSI bus
technology from the mid 1980s, and uses the standard SCSI command set.
serial communications controller (SCC)
A type of communications controller. Each quad-integrated communications controller (QUICC)
has four SCCs to handle the two Ethernet ports and the two wide area network (WAN) ports.
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