Image forming system with memory duplex printing

An image forming system for forming an image on both surface sides of a sheet of paper, comprising:

• random access memory means for storing video data to be printed on a sheet of paper;
• printing means reading out the video data stored in the random access memory means and printing an image formed by the video data on the sheet in either one of a plurality of predetermined both side print modes, said printing means comprising:
• transporting means for transporting the sheet of paper along a predetermined transportation path including a loop path section;
• inverting means located in said loop path section for turning the paper over to face the opposite direction;
• feeding means for feeding the sheet into said transportation path;
• and
• image printing means disposed at said loop path section for printing the image formed by the video data on the sheet which is being transported along said transportation path;
• the both side print modes defining different sequences of reading out the video data corresponding to one page from the video data and different sequences of printing on two surfaces of sheets, one of the both side print modes being selected depending on the currently available memory capacity of the random access memory means;
• the both side print modes including first, second and third both side print modes, the first both side print mode being selected when the random access memory means has a large amount of currently available memory capacity, the second both side print mode being selected when the random access memory means has a medium amount of currently available memory capacity, the third both side print mode being selected when the random access memory means has a small amount of currently available memory capacity;
• the first both side print mode being a mode (MODE 3) in which the printing means alternately prints images on a front surface of a sheet of paper and a rear surface of a sheet of paper which precedes the former sheet by two sheets of paper;
• the second both side print mode being a mode (MODE 3) in which the printing means alternately prints images on a rear surface of a sheet of paper which has a front surface on which an image has been printed and on a front surface of a sheet of paper which follows the former sheet by two sheets of paper;
• and
• the third both side print mode being a mode (MODE 1) in which the printing means alternatively prints images on a front surface of a sheet of paper and a rear surface of said sheet of paper.