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interchange. The sending and receiving of data in
such a manner that the content of the data is not
altered during transmission.
internet. The worldwide collection of interconnected
networks that use the Internet suite of protocols and
permit public access.
intranet. A private network that integrates internet
standards and applications (such as Web browsers)
with an organization's existing computer networking
infrastructure.
invalidate. The action of removing a logical data unit
from cache memory because it cannot support
continued access to the logical data unit on the logical
device. The removal may be the result of a failure within
the storage controller or a storage device associated
with the logical device.
I/O. Input/Output.
I/O device. An addressable read and write unit, such
as a disk drive device, magnetic tape device, or printer.
I/O interface. An interface defined to allow input/output
operations to be performed between a host and its
associated peripheral devices.
IOA. I/O Attachment Card
IOM. 4-Slot Bay Planar
IOCC. Input/Output Channel Controller
IP. Internet Protocol.
IPL. Initial Program Load
J
java. An object oriented programming language for
portable interpretive code that supports interaction
among remote objects. Java was developed and
specified by Sun Microsystems, Incorporated.
JBOD. Just a Bunch Of Disks, a group of hard disks
that are not configured according to RAID, a subsystem
of disk drives that improve performance and fault
tolerance.
K
KB. KiloByte.
key field. The second (optional) field of a CKD record.
The field length is determined by the key length
specified in the count field. The key field contains data
written by the program that can be used to identify or
locate a given record.
kilobyte (KB). A kilobyte of storage is 10³ bytes. A
kilobyte of memory is 2¹⁰ bytes.
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VOLUME 3, ESS Service Guide
KPOH. Kilo (1000) of Power-On Hours. A unit of time
used for a measurement of MTBF.
L
LAN. Local Area Network.
Last-In First-Out (LIFO). A queuing technique in
which the next item to be retrieved is the item that has
been most recently placed in the queue.
LBA. Logical Block Address
Least Recently Used (LRU). The algorithm used to
identify and make available the cache space that
contains the least-recently used data.
LED. Light-Emitting Diode.
LIC. Licensed Internal Code.
Licensed Internal Code (LIC). Microcode that IBM
does not sell as part of a machine but licenses to the
customer, as designated in the Supplement to
Agreement for Purchase of IBM Machines. See
microcode.
LIFO. Last-In First-Out.
Light Emitting Diode (LED). A semiconductor chip
that gives off visible or infrared light when it is activated.
link address. On an ESCON interface, the portion of a
source or destination address in a frame that ESCON
uses to route a frame through an ESCON director.
ESCON associates the link address with a specific
switch port that is on the ESCON director. Equivalently,
it associates the link address with the
channel-subsystem, or control-unit link-level functions
that are attached to the switch port.
link-level facility. An ESCON term for the hardware
and logical facilities of a control unit or channel
subsystem that allows communication over an ESCON
write interface and an ESCON read interface.
Local Area Network (LAN). A computer network
located at a user's site within a limited area.
logical address. On an ESCON interface, the portion
of a source or destination address in a frame used to
select a specific channel-subsystem or control-unit
image.
logical data unit. A unit of storage which is accessible
on a given logical device.
logical device. The facilities of a logical subsystem
that the host communicates with when performing I/O
operations to a single addressable-unit over an I/O
interface. The same logical device may be accessible
over more than one I/O interface.
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