difference between cart getItemsCount() and getSummaryCount()

Question

I am displaying the total items present in the cart at header. I am able to display the count of items.

But I am bit confused between two methods of cart

1. Mage::helper('checkout/cart')->getItemsCount()
2. Mage::helper('checkout/cart')->getSummaryCount();

For me 1st one returns 1 item in cart and 2nd one returns 6 items in cart, Which is correct one and what is the difference these two functions..

Thanks.