How much hard disk space is required for System Restore to work?
In order for System Restore to function on your hard disk, it needs at least 300 MB of free space for each drive that it is to function on. System Restore will not function on disks that are smaller than 1 gigabyte (GB). If you were to turn off System Protection (the feature that creates the restore points), all restore points from that disk are deleted. Once System Protection is turned back on, new restore points will begin to be created.