Chapter 1 Introduction to a Typical PC 7
Hexadecimal Number Code
The hexadecimal code is based on the number
base 16, similar to how the binary code is based
on the number base 2. The hexadecimal number
system is a computer code system that uses
16 characters. See Figure 1-8.
The hexadecimal system uses numerals 0
through 9 from the decimal number system and
six additional characters from the alphabet, A
through F. This combination of number and letter
characters forms the hexadecimal number system.
The original photo is mounted on
the rotating drum. A light transmitter
and receiver convert the light and dark
areas of the image into matching
voltage levels.
Original news photograph.
Copy converted from electrical signal back to photograph.
The first facsimilie or “telephotography” machine was put into commercial use in 1924. A transparency of a
photograph was placed on a spinning drum. The image was converted into electrical signals representing the light and
dark areas in the photograph. The electrical signals were converted back into a photographic image at the destination.
Data is converted into electrical signals.
The signals are carried across telephone
lines to the destination telephoto
machine where the image is recreated.
A transducer moves along the
drum while it spins, converting the
image into electrical signals.
A writing stylus converts the
electrical signals into an image.
Rotating drum.
Electronic voltage levels
converted to drawing.
Goodheart-Willcox Publisher
Figure 1-7. Voltage highs and lows can be used to send pictures across phone lines.