Specifications

the data in the key field and use the key field to identify
or locate a given record. The subsystem does not use
the key field.
kilobyte (KB). (1) For processor storage, real, and
virtual storage, and channel volume, 2
10
or 1024 bytes.
(2) For disk storage capacity and communications
volume, 1000 bytes.
Korn shell. Interactive command interpreter and a
command programming language.
KPOH. See thousands of power-on hours.
L
LAN. See local area network.
last-in first-out (LIFO). A queuing technique in which
the next item to be retrieved is the item most recently
placed in the queue. (A)
LBA. See logical block address.
LCU. See logical control unit.
least recently used (LRU). (1) The algorithm used to
identify and make available the cache space that
contains the least-recently used data. (2) A policy for a
caching algorithm that chooses to remove from cache
the item that has the longest elapsed time since its last
access.
LED. See light-emitting diode.
LIC. See licensed internal code.
licensed internal code (LIC). Microcode that IBM
does not sell as part of a machine, but licenses to the
customer. LIC is implemented in a part of storage that is
not addressable by user programs. Some IBM products
use it to implement functions as an alternate to
hard-wired circuitry.
LIFO. See last-in first-out.
light-emitting diode (LED). A semiconductor chip that
gives off visible or infrared light when activated.
link address. On an ESCON or FICON interface, the
portion of a source or destination address in a frame
that ESCON or FICON uses to route a frame through
an ESCON or FICON director. ESCON or FICON
associates the link address with a specific switch port
that is on the ESCON or FICON 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. The ESCON or FICON hardware
and logical functions of a control unit or channel
subsystem that allow communication over an ESCON or
FICON write interface and an ESCON or FICON read
interface.
local area network (LAN). A computer network
located on a user’s premises within a limited geographic
area.
local e-mail. An e-mail configuration option for storage
servers that are connected to a host-system network
that does not have a domain name system (DNS)
server.
logical address. On an ESCON or FICON interface,
the portion of a source or destination address in a frame
used to select a specific channel-subsystem or
control-unit image.
logical block address (LBA). The address assigned
by the ESS to a sector of a disk.
logical control unit (LCU). See control-unit image.
logical data unit. A unit of storage that is accessible
on a given device.
logical device. The facilities of a storage server (such
as the ESS) associated with the processing of I/O
operations directed to a single host-accessible emulated
I/O device. The associated storage is referred to as a
logical volume. The logical device is mapped to one or
more host-addressable units, such as a device on an
S/390 I/O interface or a logical unit on a SCSI I/O
interface, such that the host initiating I/O operations to
the I/O-addressable unit interacts with the storage on
the associated logical device.
logical partition (LPAR). A set of functions that create
the programming environment that is defined by the
ESA/390 architecture. ESA/390 architecture uses this
term when more than one LPAR is established on a
processor. An LPAR is conceptually similar to a virtual
machine environment except that the LPAR is a function
of the processor. Also the LPAR does not depend on an
operating system to create the virtual machine
environment.
logical path. For Copy Services, a relationship
between a source logical subsystem and target logical
subsystem that is created over a physical path through
the interconnection fabric used for Copy Services
functions.
logical subsystem (LSS). Pertaining to the ESS, a
construct that consists of a group of up to 256 logical
devices. An ESS can have up to 16 CKD-formatted
logical subsystems (4096 CKD logical devices) and also
up to 16 fixed-block (FB) logical subsystems (4096 FB
logical devices). The logical subsystem facilitates
configuration of the ESS and may have other
implications relative to the operation of certain functions.
There is a one-to-one mapping between a CKD logical
subsystem and an S/390 control-unit image.
194 ESS Host Systems Attachment Guide
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