customization.
Procedures
that
tailor
the
controller
microcode
to
fit
the
various
types of
display
stations
and
printers
and the method of host
attachment
that a
particular
controller
will
handle.
D
data link. Any physical link,
such
as a
wire
or
a
telephone
circuit,
that
connects one
or
more
devices
or
communication
controllers.
data
processing
(OP). The
systematic
performance
of
operations
upon data;
for
example,
handling,
merging,
sorting, computing.
data
stream. (1)
All
data
transmitted
through
a data
channel in a
single
read
or
write
operation. (2) A
continuous
stream
of
data
elements
being
transmitted,
or
intended for·
transmission,
in
character
or
binary-digit
form,
using
a defined format. See also data
stream format.
data
stream
format.
In SNA, the
format
of the data
elements (end-user data) in the request
unit
(RU). See
also
3270 data stream.
Data
Terminal
Ready (OTR)
flow
control.
A
procedure
for
a
communicating
device
to
signal
its readiness to
receive
data
by
raising
the DTR lead on an EIA
2320
interface.
decrypt. To
convert
encrypted
data into
clear
data.
Contrast
with
encrypt.
device. A
mechanical,
electrical,
or
electronic
contrivance
with
a
specific
purpose.
direct
access
storage
device.
(1) A
storage
device
that
provides
direct
access
to
data.
(2)
See
also
immediate
access storage and random access
memory.
disk. A
direct-access
data
storage
medium,
which
may
be
either
flexible
(diskette)
or
hard
(fixed disk).
diskette. A
flexible
magnetiC
disk
enclosed in a
protective
container.
diskette
drive.
The
mechanism
used to seek, read,
and
write
data on diskettes.
display
field. (1) An
area
in the
display
buffer
that
contains a
set
of
characters
that
can be
manipulated
or
operated upon as a unit.
(2)
A
group
of
consecutive
characters
(in the buffer)
that
starts
with
an
attribute
character
(defining the
characteristics
of
the field) and
contains one
or
more
alphanumeric
characters.
The
field
continues
to, but
does
not
include, the
next
attribute
character.
display
station. An
input/output
device
containing
a
display
screen
and an attached keyboard
that
allows
a
user
to
send
information
to
or
receive
information
from
the system.
distributed
function
terminal
(OFT). A
programmable
terminal
that can
perform
operations
previously
performed
by the
controller.
These
terminals
can
interpret
the 3270 data
stream
themselves. Examples
are
the IBM 3270 Personal
Computer
and the 3290
Information Panel.
distributed
function
terminal
(OFT) mode. A
host-interactive
mode
that
enables an IBM 3270
Information Display System customized in
this
mode
to
run as
many
as
four
host sessions. The
sessions
can
emulate
a
3178,3179,3278
Model 2,
or
3279 Model
S2A.
downstream.
(1)
In the
direction
of data
flow
or
toward
the
destination
of
transmission.
(2)
From the
processor
toward
an attached
unit
or
end user.
(3) Contrast
with
upstream.
downstream
load (OSL). The
capability
of a
distributed
function
terminal
to
receive
its
control
program
from
the
controller
to
which
it
is attached. A
diskette
containing
the
terminal's
control
program
is loaded into
the
controller.
duplex. Pertaining
to
communication
in
which
data
can be sent and received at the
same
time.
Synonymous
with
full duplex.
E
EIA
communication
adapter. A
communication
adapter
conforming
to EIA
standards
that can
combine
and
send
information
on
two
lines
at speeds up
to
19.2
kbps.
EIA 2320. An
electrical
interface defined by the
Electronics
Industries
Association for
establishing
connections and
controlling
data
flow
between
data
terminal
equipment
and
data
communication
equipment. The interface has been adapted
to
allow
communication
between DTEs.
emulation.
(1)
The
imitation
of all
or
part
of one
system by another,
primarily
by
hardware,
so
that
the
imitating
system accepts the
same
data,
executes
the
same
programs,
and achieves the
same
results as the
imitated
computer
system.
(2)
The use of
programming
techniques
and special
machine
features
to
permit
a
computing
system
to execute
programs
written
for
another
system. (3) Imitation;
for
example,
imitation
of a
computer
or
device.
(4)
See
terminal
emulation.
(5)
Contrast
with
simulation.
encrypt. To
scramble
data
or
convert
it, before
transmission,
to
a
secret
code
that masks the
meaning
Glossary
X-7
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