why does a computer registry size changes?

Solution
The registry size changes when you install and unistall software and drivers because that is where they store their initilization and component linkage information.

Some applications use it as a storage area for inter and intra process communication and then delete their registry entries when the application is closed.

There are probably more reasons but that's the general outline - the registry is a semi-permanent storage area. It's permanent between shutdowns and variable when things are installed/unistalled or intialized and then shut down.
The registry size changes when you install and unistall software and drivers because that is where they store their initilization and component linkage information.

Some applications use it as a storage area for inter and intra process communication and then delete their registry entries when the application is closed.

There are probably more reasons but that's the general outline - the registry is a semi-permanent storage area. It's permanent between shutdowns and variable when things are installed/unistalled or intialized and then shut down.
 
Solution