Q. Explain Keyboard Input and Video output ?

A Keystroke read from keyboard is termed as a console input and a character displayed on the video screen is known as a console output. In assembly language reading and displaying character is most tiresome to program. Though these tasks were greatly simplified by convenient architecture of 8086/8088. Thatarchitecture offers for a pack of software interrupt vectors starting at address 0000:0000.

The benefits of this type of call is that it appears static to a programmer however flexible to a system design engineer. For illustration INT 00H is a special system level vector which points to the 'recovery from division by zero' subroutine. If new designer come and want to move interrupt location in memory it adjusts entry in the IVT vector of interrupt 00H to a new location. So from the system programmer point of view it's relatively easy to change vectors under program control.