Arrays let us store a list of items with fast access, but are of fixed size. Linked lists give us a data structure to store a list of items that grows and shrinks as the number of items changes. However, linked lists are not very efficient in two ways. They require a pointer for every data item $($two pointers for a doubly$-$linked list$),$ so seem to waste space. They also can be slow $($relatively speaking$)$ for two reasons. First, creating and deleting nodes takes time. Second, following the pointers takes time, primarily because of how memory access works. $($This is related to CPU cache behaviour, which we will have a class on a bit later.$).$