A super computer is a computer which performs at a rate of speed which is far above that of other computer. 

Note: The primary use of supercomputer is in scientific computing which requires high speed computer to perform complex calculation.

Light travelling in an optical fiber loses power over distance. The loss of power depends on the wavelength of the light and on the propagating material. For silica glass,the shorter wavelength are attenuated the most. The lowest loss occurs at the 1550-nm wavelength, which is commonly used for long transmission. So the amount of attenuation for given cable is wavelength dependent.

Each row in a relation is called a tuple. A tuple defines a collection of attributes values.

The Modem or router is a transmitter and can’t give computer a virus, but they can both transmitter and can’t give computer a virus, but they can both transmit it if it is sent through them. They just pass on what is fed to them. They can’t hold on viruses.

The port numbers in the range from 0 to 1023 are the well known ports. They are used by system processes that provide widely used type of network services. By default HTTP uses port 80.

Central processing unit is the part of a computer that performs logical and arithmetical operation on the data as specified in the instructions.

A personal digital assistant (PDA), also known as a handheld PC is a mobile device that functions as a personal information manager.

A hard copy is a printed copy of information from a computer. Sometimes referred to as a printout, a hard copy is so-called because it exists as a physical object.

Batch processing is the execution of a series of programs on a computer without manual intervention. All input parameters are predefined through scripts, command-line arguments, control files or job control language. Rather than running one program multiple times to process one transaction each time, batch processes will run the program only once for many transactions, reducing system overhead. 

A Relation is a set of tuples .Each row is unique. Rows are unordered. we can display them in any way we like and the meaning doesn’t change.