about first question: perhaps you have misunderstood my meaning. I didn't copy the big file in my application.Instead, I switched to the window's explore to do this task, so my application can't handle something(such as update the interface in real-time , send a signal to the comport's DTR when I received some special bytes from the comport),and these only can do after the file's copying is ended. About question 2: Can you give me some good advices ? :laugh: Have a nice day! No money is a terrible thing!

Two question: 1. My program must monite the communication port in real-time mode,and display the trend-line in the screen,but when i do another long task,such as copy a big file to the floppy disk, It seem that the program's interface can't updated until this long task has finished, what shoud I do in such case? 2. when I drag another application's window, It seem that the WM_TIMER message only occured after I release the mouse-button,but I don't want this ,what do I do in such case? Thanks a lot!