Hi Poya22, the problem is that FCUSB is not like those legacy "universal" programmers. And it doesn't operate the same. Those software were designed for data that was typically 8Mbit-16Mbit density chips. So the software was designed around a "buffer screen", where you could load data into the buffer (either via file, or reading another chip), modify the buffer with manual inputs, compare the buffer against the current data, and write the buffer back to the chip. That buffer was stored in "RAM".
FlashcatUSB uses real-time streaming. The data in the window is filled, at the time, it is viewed. If you scroll down, you are literally streaming the data from the Flash device in real-time. This method is ideal for Flash devices that are very large (8Gbit is currently the highest supported density in the Flash library, and 64Gbit/128Gbit support is in development). It would be impracticable to "buffer" that kind of data.
So I propose a solution. How about a button that says "Verify", when you click it, it will allow you to select a file, prompt you for an offset, and then check to see if that file is in the Flash, and if not, how many bytes differ? Would that work for you?