SIGNAL
In the fields of communications, signal processing, and in electrical engineering more generally, a signal is any time-varying quantity. Signals are often scalar-valued functions of time (waveforms), but may be vector valued and may be functions of any other relevant independent variable.
Sound. Since a sound is a vibration of a medium (such as air), a sound signal associates a pressure value to every value of time and three space coordinates. A microphone converts sound pressure at some place to just a function of time, using a voltage signal as an analog of the sound signal.
Compact discs (CDs). CDs contain discrete signals representing sound, recorded at 44,100 samples per second. Each sample contains data for a left and right channel, which may be considered to be a 2-vector (since CDs are recorded in stereo).
Pictures. A picture assigns a color value to each of a set of points. Since the points lie on a plane, the domain is two-dimensional. If the picture is a physical object, such as a painting, it's a continuous signal. If the picture a digital image, it's a discrete signal. It's often convenient to represent color as the sum of the intensities of three primary colors, so that the signal is vector-valued with dimension three.
SYSTEM
1. A group of related components that interact to perform a task.
2. A "computer system" is made up of the CPU, operating system and peripheral devices. All desktop computers, laptop computers, network servers, minicomputers and mainframes are computer systems. Most references to "computer" imply the "computer system
3.An "information system" is a business application made up of the database, the data entry, update, query and report programs as well as manual and machine procedures. Order processing systems, payroll systems, inventory systems and accounts payable systems are examples of "information systems