help me understand system restore points vista?

[kmufc77]

hi im running vista 32 bit with system restore turned on the drive with vista installed.a few days ago i had about 15 restore points automacially saved from the last few weeks,however today all i have is one restore point which is saved about a hour ago where have the other restore points gone? i havent deleted them?having system restore on is pointless with having just one restore point which was saved about a hour ago if something goes wrong with my pc im stuffed, i dont understand where the rest of the restore points have dissapered does vista automacially delete then make a number a new ones or a regualry basis as i wanted restore points that give me a few days previous always as a backup.can someone please explain why im having this problem or is it vista automacially doing this by default