How much disk space does System Restore require?
To store restore points, you need at least 300 megabytes (MB) of free space on each hard disk that has System Protection turned on. System Restore might use up to 15 percent of the space on each disk. As the amount of space fills up with restore points, System Restore will delete older restore points to make room for new ones.
System Restore will not run on disks smaller than 1 gigabyte (GB).