If you were searching for a particular element, you might easily have to look at the whole list before you find the one that you need. Linux uses another technique, hashing to get around this restriction. A hash table is an array or vector of pointers. An array, or vector, is simply a set of things coming one after another in memory. A bookshelf could be said to be an array of books.
Arrays are accessed by an index , the index is an offset into the array.
A hash table is an array of pointers to data structures and its index is derived from information in those data structures. If you had data structures describing the population of a village then you could use a person's age as an index. To find a particular person's data you could use their age as an index into the population hash table and then follow the pointer to the data structure containing the person's details. However, searching these shorter chains is still faster than searching all of the data structures. As a hash table speeds up access to commonly used data structures, Linux often uses hash tables to implement caches .