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Unformatted text preview: s system bus outside the computer by way of a cable, and just as you can plug
one extension cord into another to lengthen the circuits, you can plug one SCSI device
into another to form a daisy chain. Most current implementations of SCSI limit the
number of devices that can be connected together to form a daisy chain to seven due to
the bus capacity limitation. This can really save you expansion slots in your computer for
connecting other devices. If none of your computer's device controller cards has a SCSI
interface, you can purchase a separate SCSI interface (as the one shown in Figure 9.42) to
plug into an existing parallel port to which you can connect additional SCSI devices. Dumb, Smart and Intelligent Terminals
Terminals (monitors along with keyboards) are extensively being used today as online,
remote data entry devices. Depending on their local processing capability, these terminals
are classified as dumb, smart and intelligent.
A dumb terminal is a simple, low-cost terminal with alphanumeric display capability. It
has a keyboard for input, a means of communication with the CPU of the main computer,
and a screen to display the entered data and output received from the main computer.
Dumb terminals need not appear dumb to the user. Because of the rapidity with which the
main computer can communicate back to the terminal, many applications are not affected
if no actual processing is done locally at the terminal. However, dumb terminals transmit
all data directly to the main computer. This type of data is called "dirty" data because
errors are transmitted along with good data. The errors are then identified and informed
to the terminal operator by the CPU of the main computer and processing could be
delayed until "clean" data are obtained from the operator. This type of delay,
accompanied by the need to process the data over again, can be expensive.
A smart terminal usually has a microprocessor (a CPU) and some internal storage in
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This document was uploaded on 04/07/2014.
- Spring '14