IBM 990 - Manual (Page 266)

254 IBM ^ zSeries 990 Technical Guide
core . (1) In an optical cable, the central region of an
optical fiber through which light is transmitted. (2) In an
optical cable, the central region of an optical fiber that
has an index of refraction greater than the surrounding
cladding material. See also cladding and optical fiber.
coupler. In an ESCON environment, link hardware
used to join optical fiber connectors of the same type.
Contrast with adapter.
CPC. Central Processor Complex
CTC. (1) Channel-to-channel. (2) Mnemonic for an
ESCON channel attached to another ESCON channel.
CVC. Mnemonic for an ESCON channel attached to an
IBM 9034 convertor. The 9034 converts from ESCON
CVC signals to parallel channel interface (OEMI)
communication operating in block multiplex mode (Bus
and Tag). Contrast with CBY.
DDM. See disk drive module.
dedicated connection. In an ESCON Director, a
connection between two ports that is not affected by
information contained in the transmission frames. This
connection, which restricts those ports from
communicating with any other port, can be established
or removed only as a result of actions performed by a
host control program or at the ESCD console. Contrast
with dynamic connection. Note: The two links having a
dedicated connection appear as one continuous link.
default. Pertaining to an attribute, value, or option that
is assumed when none is explicitly specified.
destination. Any point or location, such as a node,
station, or a particular terminal, to which information is
to be sent.
device address. In the ESA/390 architecture and the
z/Architecture, the field of an ESCON or FICON (FC
mode) device-level frame that selects a specific device
on a control-unit image.
device number. (1) In the ESA/390 architecture and
the z/Architecture, a four-hexidecimal-character
identifier, for example 19A0, that you associate with a
device to facilitate communication between the
program and the host operator. (2) The device number
that you associate with a subchannel that uniquely
identifies an I/O device.
device. A mechanical, electrical, or electronic
contrivance with a specific purpose.
direct access storage device (DASD). A mass
storage medium on which a computer stores data.
disconnected. In an ESCON Director, the attribute
that, when set, removes a dedicated connection.
Contrast with connected.
disk drive module (DDM). A disk storage medium that
you use for any host data that is stored within a disk
subsystem.
Disk. A physical or logical storage media on which a
computer stores data (is also sometimes referred to as
a magnetic disk).
distribution panel. (1) In an ESCON or FICON
environment, a panel that provides a central location
for the attachment of trunk and jumper cables and can
be mounted in a rack, wiring closet, or on a wall.
duplex connector. In an ESCON environment, an
optical fiber component that terminates both jumper
cable fibers in one housing and provides physical
keying for attachment to a duplex receptacle.
duplex receptacle. In an ESCON environment, a fixed
or stationary optical fiber component that provides a
keyed attachment method for a duplex connector.
duplex. Pertaining to communication in which data or
control information can be sent and received at the
same time. Contrast with half duplex.
dynamic connection. In an ESCON Director, a
connection between two ports, established or removed
by the ESCD and that, when active, appears as one
continuous link. The duration of the connection
depends on the protocol defined for the frames
transmitted through the ports and on the state of the
ports. Contrast with dedicated connection.
dynamic connectivity. In an ESCON Director, the
capability that allows connections to be established
and removed at any time.
Dynamic I/O Reconfiguration . A S/390 function that
allows I/O configuration changes to be made
non-disruptively to the current operating I/O
configuration.
EMIF. See ESCON Multiple Image Facility.
Enterprise System Connection (ESCON). (1) An
ESA/390 computer peripheral interface. The I/O
interface uses ESA/390 logical protocols over a serial
interface that configures attached units to a
communication fabric. (2) A set of IBM products and
services that provide a dynamically connected
environment within an enterprise.
Enterprise Systems Architecture/390® (ESA/390).
An IBM architecture for mainframe computers and
peripherals. Processors that follow this architecture
include the S/390 Server family of processors.