A user invokes an app that writes a file. The app displays a progress bar that shows how much of the file has been written. Just as the progress bar reaches 50%, the battery fails and the device crashes. When the user reboots the device, he or she discovers that less than 20% of the file has actually been written. Explain why the app reported writing 50%. Frame your answer in terms of the design of I/O device drivers.

The app reported writing 50% before the battery fails is because while writing, the data is been saved in the secondary memory via a buffer and not directly to the primary memory ( RAM ) and its returned from the secondary memory via the buffer to the primary memory

Explanation:

The app reported writing 50% before the battery fails is because while writing, the data is been saved in the secondary memory via a buffer and not directly to the primary memory ( RAM ) and its returned from the secondary memory via the buffer to the primary memory

What the app displays as a progress bar is from the Buffer, this is because as the developer was designing the app he wanted the data entry to be very fast  hence he had to send the file through a buffer with the aid of a workstation he designed. so if the secondary storage is slow in returning the data  back to the primary memory as fast as it entered the secondary memory via the Buffer, Then the percentage of the file that would be displayed as written when the system reboots will be less than what the app displayed before the reboot i.e. 20% < 50%