System Restore creates regular scheduled checkpoints even if you have not made any changes to the system. System Restore automatically creates these checkpoints:
Every 10 hours that your computer is on
Every 24 hours in real time
If your computer is off for more than 24 hours, System Restore will create a checkpoint the next time you turn it on. The computer must be idle for a few minutes before System Restore will create a scheduled checkpoint.
To give System Restore more disk space to save information.
Open System properties in Control Panel.
Click the Performance tab, and then click File System.
On the Hard Disk tab, move the System Restore disk space use slider to allot more space for System Restore.
Click Apply, and then OK.
If you do not click Apply, the changes will not be saved when you click OK and close the dialog box.
System Restore requires at least 200 MB of free space on the hard disk (or partition that contains your Windows System folder). For the best performance and protection, you should try to allocate more space than that.
By default, when Windows installs System Restore on your computer, it allocates about 12 percent of your disk space for storage.