Chapter 2 • Computer Systems 21memory of the bank’s computer. Optical character
recognition (OCR)is an input method that directly scans
typed, printed, or hand-printed material. A device called an
optical character reader scans and recognizes the charac-
ters and then transmits the data to the computer memory or
records them on some type of digital media.
Imaginggoes even further than OCR. With imaging,
any type of paper document, including business forms,
reports, charts, graphs, and photographs, can be read by a
scanner and translated into digital form so that the docu-
ment can be stored in the computer system. Then this
process can be reversed so that the digitized image stored
in the computer system can be displayed on a video display
unit, printed on paper, or transmitted to another computer.
An increasingly important way of entering data into
a computer is by scanning a bar code labelon a package,
a product, a routing sheet, a container, or a vehicle. Bar
code systems capture data much faster and more accurate-
ly than systems in which data are keyed. Thus the use of
bar codes is very popular for high-volume supermarket
checkout, department store sales, inventory tracking, time
and attendance records, and health care records. There is
actually a wide variety of bar code languages, called
symbologies. Perhaps the most widely known symbology
is the Universal Product Code, or UPC, used by the gro-
cery industry.
Of course, if the data are already stored in computer-
readable form, such as on a compact disk (CD) or a digital
video disk (DVD), they can be input into the computer via
a CD drive or a DVD drive. These devices can also serve as
output devices if the data will be read back later into either
the same or another computer.
Just as we must have a way of entering data into the
computer, the computer must have a way of producing
results in a usable form. We have already mentioned
displaying results on a video display unit, printing a docu-
ment on a small printer built into a special-purpose termi-
nal, or writing output on a CD or a DVD.
The dominant form of output, however, is the printed
report. Computer printers come in a variety of sizes, speeds,
and prices. The printers used with PCs usually employ a
nonimpact process (such as an ink-jet process), and they
typically operate in a speed range of 5 to 50 pages per
minute. Printers used with larger computers may be impact
or nonimpact printers. Impact printers operate at speeds up
to 2,000 lines per minute and print one line at a time, usually
employing an impact printing mechanism in which
individual hammers force the paper and ribbon against
the appropriate print characters (which are embossed on a
rotating band or chain). Nonimpact printers often employ an
electrophotographic printing process (similar to a copying
machine); cut-sheet printers operate at speeds up to
135 pages per minute, while continuous-form printers may
reach speeds up to 1,800 pages per minute.
In part to counteract the flood of paper that is threat-
ening to engulf many organizations, microfilm has become
an important computer output medium. The output device
is a computer output microfilm (COM)recorder that
accepts the data from the memory and prepares the micro-
film output at very high speeds, either as a roll of micro-
film or as a sheet of film called a microfiche that contains
many pages on each sheet. Voice response unitsare gain-
ing increasing acceptance as providers of limited, tightly
programmed computer output.
To summarize, the particular input and output
devices attached to a given computer will vary based on
the uses of the computer. Every computer system will have
at least one input device and at least one output device. On
the computers you will be using as a manager, keyboards,
mice, video display units, printers, and CD/DVD drives
will be the most common input/output devices.Computer Memory
At the heart of the diagram of Figure 2.1 is the memory,
also referred to as main memory or primary memory. All
data flows are to and from memory. Data from input
devices always go into memory; output devices always
receive their data from memory; two-way data flows
exist between files and memory and also between the
arithmetic/logical unit and memory; and a special type
of data flows from memory to the control unit to tell the
control unit what to do next. (This latter flow is the focus
of the section of this chapter “The Stored-Program
Concept.”)
In some respects, the computer memory is like
human memory. Both computers and humans store data in
memory in order to remember it or use it later. However,
the way in which data are stored and recalled differs radi-
cally between computer memory and human memory.
Computer memory is divided into cells, and a fixed
amount of data can be stored in each cell. Further, each
memory cell has an identifying number, called an address,
which never changes. A very early microcomputer, for
example, might have 65,536 memory cells, each capable of
storing one character of data at a time. These cells have
unchanging addresses varying from 0 for the first cell up to
65,535 for the last cell.
A useful analogy is to compare computer memory to
a wall of post office boxes (see Figure 2.2). Each box has
its own sequential identifying number printed on the box’s
door, and these numbers correspond to the addresses asso-
ciated with memory cells. In Figure 2.2, the address or
identifying number of each memory register is shown in