One of the functions of the control unit is:

It tells the computer's memory, arithmetic/logic unit(ALU) and input - output devices (I/0) How to respond to a program's instructions ?

Explain that 

(Support the answer with a graphic if possible).

Control Unit

Control unit refers to as a component found in the Central Processing Unit (CPU) of a computer which basically gives directions to the computer processors.

The application's writing file contains a storage in a secondary storage which became slower as compared to the primary storage. Therefore, when the file the file was written, it was sent to the Random-Access Memory (RAM) to which buffering took place.

From the Random-Access Memory (RAM), the writing file was later stored in the secondary storage which basically is contained in memory cards and hard drives. Here, the development of the application goes under various tasks which illustrates that the application is designed to rate the amount of data that is being used in workstations that contains a high transferring rate for them to lack any problem that may arise.

Step-by-step explanation

From the above definition, it is clear that when the user is using the application secondary storage with low transferring speed because the progress bar relies on the buffering data. So, when the system is off, the buffering data is also deleted or cleared and hence it is not written in the secondary storage and when the power is restored, the system will check the fata that was written before the turning off which will in turn show the difference in the progress bar. If the secondary storage had high transferring rate then the progress bar after the system being off will be more and if the rate was low, then the progress rate will even be lower than the percentage seen before turning off.