IBM E10, Service Manual, Page: 262 / 279

data field. The third (optional) field of a CKD record.
The field length is determined by the data length
specified in the count field. The data field contains data
written by the program.
data record. A data records are stored on a track
following the track-descriptor record. The data records
are numbered consecutively starting with 1. A maximum
of 255 data records can be stored on a track. Each data
record consists of a count field, a key field (optional),
and a data field (optional).
data sharing. The ability of the similar or different host
systems to concurrently utilize information that they
store on one or more storage devices. The storage
facility allows configured storage to be accessible to any
attached host systems, or to all. To use this capability,
the host programs need to be designed to support data
sharing.
dedicated storage. Storage within a storage facility
that is configured so that a single host has exclusive
access to the storage.
demote. The action of removing a logical data unit
from cache memory. A data unit is demoted in order to
make room for other logical data units in the cache or
because the logical data unit was invalidated. Logical
data units with active write unit must be destaged
before being demoted.
destage. (1) The process of reading data from cache.
(2) The action of storing a logical data unit in cache
memory with active write data to the storage device. As
a result, the logical data unit changes from cached
active write data to cached read data.
device. The ESA/390 term for a logical device.
Device Adapter (DA). A physical sub-unit of a storage
controller, the SSA device card, that provides the
facilities to attach to one or more interfaces used to
communicate with the associated storage devices.
device address. The ESA/390 term for the field of an
ESCON device-level frame that selects a specific device
on a control-unit image.
device interface card. A physical sub unit of a
storage cluster that provides the communication with the
attached DDMs.
device number. The ESA/390 term for a
four-hexadecimal-character identifier (e.g. X'13A0')
associated with a device to facilitate communication
between the program and the host operator. The device
number is associated with a subchannel.
device sparing. When a subsystem automatically
copies data from a failing DDM to a spare DDM. The
subsystem maintains data access during the process
disk drive. The mechanism used to seek, read, and
write information on a disk.
disk drive module. The primary nonvolatile storage
medium that you use for any host data that is stored
within a subsystem. Number and type of storage
devices within a storage facility may vary.
drawer. A unit that contains multiple DDMs, and
provides power, cooling, and related interconnection
logic to make the DDMs accessible to the attached host
systems.
E
EBCDIC. Extended Binary-Coded Decimal Interchange
Code. A coding scheme developed by IBM which is
used to represent various alphabetic, numeric, and
special symbols with an 8 bit code.
EC. Engineering Change. A update to a machine, part,
or program. Each EC for a given unit is assigned a
unique number referred to as an EC level or EC
number. The initial release of a unit normally has an
associated EC level.
ECC. Error Correction Code.
ECKD. Extended Count Key Data. An extension of the
CKD architecture.
electrostatic discharge (ESD). An undesirable
discharge of static electricity that can damage
equipment and degrade electrical circuitry.
EMIF. ESCON Multiple Image Facility. An ESA/390
facility that allows LPARs to share an ESCON channel
path by providing each LPAR with its own
channel-subsystem image.
enclosure. See rack.
end-of-file record. On a CKD DASD device, end of
file is indicated by a record with a data length of zero.
EPOW. Early Power-Off Warning.
EPROM. Erasable Programmable Read-Only Memory.
ERP. Error Recovery Procedure.
Exception Symptom Code (ESC). A two byte error
code that describes the exception: class, type, and
symptom.
ESA/390. Enterprise Systems Architecture/390. An
IBM architecture for mainframe computers and
peripherals. Processor systems following this
architecture include the ES/9000 family.
ESC. Exception Symptom Code.
246
VOLUME 3, ESS Service Guide