Complex sentence: The memory of a process consisted solely of segments which were mapped into its address space; to read or write to them, the process simply used normal CPU instructions, and the operating system took care of making sure that all the modifications were saved to disk.
Split into simpler sentences: The memory of a process consisted solely of segments which were mapped into its address space. To read or write to them, the process simply used normal CPU instructions, and the operating system took care of making sure that all the modifications were saved to disk.