1024 bytes = 1 kilobyte 1024 kilobytes = 1 megabyte 1024 megabytes = 1 gigabyte 1024 gigabytes = terabyte.
Most hard drives these days on new pc come with at least 500 gbytes and many now are providing 1 terabyte. I would suggest that your main drive C: partition should be at least 500 Gbyte unless it is ONLY for the operating system and all other data and programs on another partition. Then drive C: could be smaller. Its always a good idea to have a recovery disc on a separate CD/DVD