Your Pc is a digital device. He performs most tasks by turning a series of electronic switches.
A binary 0 - represented here by a sphere - indicates a button off. A binary 1 - here represented by a cube
- Indicates a button on. There is no intrinsic distinction. The design of a digital code would look like this:
The phone system is an analog device, designed - at a time when digital electronics was unknown - for
convey the various sounds and tones of the human voice. These sounds are electronically converted into an analog signal as a continuous current that varies gradually power and frequency.
Can be described by means of oscilloscope as a wavy line like this:
The modem is a bridge between analog and digital signals. It converts the digital data on and off at a sign
Analog varying or modulating the frequency of a wave machine, a process similar to that used by stations
FM. As the receiving end of an electronic connection, the modem does exactly the opposite: demodulates the analog signals digital codes. The two terms, modular and demodulating, gave his name to the modem.
The modem communication involves three elements less standard personal computers - serial ports, the
modem commands and communication program (see How It Works Serial Port). The inconsistencies make it impossible describe a universal form of operation for all modems, but the modes of operation discussed here describe precisely most programs that use a standard Hayes modem with 25 pin serial port.
Source: Evolution of Computers
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