Sometimes when modifying a document with a word processor ad

Sometimes, when modifying a document with a word processor, adding text does not increase the appartent size of the file in mass storage, but at other times the addition of a single symbol can increase the apparent size of the file by several hundred bytes. Why?

Solution

Storage space is allocated in units of physical sectors (actually in units of groups of sectors in most cases). If the last physical sector is not full, additional text can be added without increasing the storage space allocated to
the file. If the last physical sector is full, any addition to the document will require additional physical sectors to be allocated.