How to process 360 GB file within a minute

Question

I have processed a 3 GB binary file within three minute using a single thread.Here processing meant that I have read the file and loaded onto memory and applied a small buisness logic while processing the data.The program is taking 3 minutes as a processing time If I use multithreading in the program, it is taking 4 minutes (more time) to process that data . If we compre the two procesing time(single thread ,multithreads) the multithread program is taking more time.Generally speaking multithreading should give good performance .Here performance is meant that processing time. Here I observed the multithread programing while switching between the threads ,the threads are taking some tiny time.In the tiny time those theards are in idle state. The above program is only for testing 3 GB data. But my intension is to process the 360 GB data with a minutes. Please give your thoughts about it.