Technique for controlling screen size of monitor adapted to GUI environment

A circuit for controlling a partial magnification of a monitor screen, comprising:

• a microcomputer mounted in a monitor, said microcomputer containing a magnification control program for controlling the magnification of the monitor screen, said microcomputer receiving horizontal and vertical synchronization signals and generating horizontal and vertical control signals in response to said horizontal and vertical synchronization signals;
• a horizontal and vertical signal processor for receiving said horizontal and vertical control signals and a vertical voltage control signal from said microcomputer and outputting horizontal and vertical correction signals and horizontal and vertical oscillator signals according to those horizontal and vertical control signals;
• a horizontal driving circuit for supplying a horizontal current to a horizontal deflection yoke circuit in response to said horizontal oscillator signal, said horizontal deflection yoke and generating a horizontal sawtooth wave current for horizontally synchronizing video signals displayed on the monitor screen in response to said horizontal correction signal and said horizontal current;
• an S-shaped correcting and switching circuit receiving an S-shaped correcting signal from the microcomputer generating a correction waveform for output to said horizontal deflection yoke for S-shaped correction, and said S-shared correcting and switching circuit receiving a switching control signal output from the microcomputer for controlling an on/off switch to control the horizontal size of a portion of the screen;
• and
• a vertical deflection circuit for receiving the vertical correction signal and the vertical oscillator signal output from the horizontal and vertical signal processor according to the vertical voltage control signal for magnifying the vertical size of the monitor screen, and for transferring a vertical sawtooth wave current to a vertical deflection yoke circuit.