Terminals were originally categorized as
interactive or remote batch, the latter also commonly referred to as a remote
job entry device. An interactive terminal is typically used to transmit
relatively short queries or to provide an operator with the ability to respond
to computer-generated screen displays by entering data into defined fields
prior to transmitting the filled in screen.
Once the data have been received, the
destination device will respond to the transmission in a relatively short
period of time, typically measured in seconds. In comparison, remote batch
terminals provide the operator with the ability to group or batch a series of
jobs that can range in scope from programs developed for execution on a large
computer to queries that are also structured for execution against a database
maintained on a large computer system.
The introduction of the personal computer
altered the previous distinction. That is, the ability to use the hard drive of
a PC as a storage mechanism enables the personal computer to transmit and
receive files that can range up to a gigabyte or more in size.
Although the distinction between
interactive and batch terminals was essentially eliminated by the PC, it is an
important topic to note as many software programs were developed to turn a
personal computer into a specific type of terminal by emulating the features of
a terminal. As you might expect, such software is referred to as terminal
emulation software.
Interactive terminal classification
One method commonly used to classify
interactive terminals is based on their. This method of terminal classification
has its origins with tletype terminals in which those terminals could be
configured as a receive only (RO), keyboard send–receive (KSR) or automatic
send–receive (ASR) device.
Receive only (RO)
A receive only (RO) terminal consists of a stand-alone
printer with a serial communications interface but lacking a keyboard.
Originally developed to simply receive messages transmitted on message
switching systems developed in the 1930s, a limited number of RO terminals are
still in use today.
Keyboard send-receive (KSR)
Originally, keyboard send–receive (KSR)
terminals included a printer, serial communications interface, and keyboard.
This permitted the terminal operator to both originate a message from the
keyboard as well as to print a received message.
Automatic send-receive (ASR)
The third interactive terminal
classification is automatic send–receive (ASR). An ASR terminal consists of a
printer, serial communications interface, keyboard and auxiliary storage. Here
the auxiliary storage permits messages to be composed ‘off-line’ with the
terminal not attached via a communications facility to its intended
transmission destination.
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