Is the actual size of the file and size on the disk is different?

Is the actual size of the file and size on the disk is different and is your system takes more time to open files stored on the disk , this may be due to the fact that you have multiple deletions on the same disk ,which creates some memory free space that affect the others files to be stored with some other size than the actual
This can be overcome by optimizing the drive
steps:
Right click on the drive for which u want to optimize
and then click on the tools tab and select optimize option and then click on the analyse and takes some time in optimizing,fragmenting,defragmenting.
However , the system optimizes the drive periodically (usually the time for the periodic optimization should be set by the user)