Internal mechanics of arrays

So far, we learned what an array is and how it solves problems where we need to store and manipulate large-scale data easily. We can now look at how the array data structure works under the hood and what makes it so fast and easy to use.

Memory addresses

Array elements are accessed using indices because arrays are stored contiguously in memory. To better understand the relationship between array elements and indices, let us revisit the memory model we learned earlier.

Memory is logically organized in RAM as a sequence of blocks, each 1 byte (8 bits) long. Every block has a unique identifier that can be used to locate it in memory, called its address. The address is nothing but a number that is the relative position of the block from the start (starting from 0).

Layout in memory

An array is just a continuous segment of memory that stores data of a single type. Each data item in the array has a fixed size equal to the size of its data type, so the total size of an array is the sum of the size of all data items.

Accessing data items

Now that we know how an array is mapped into continuous memory, it is easy to figure out a mathematical formula to calculate the address of a data item at a given index if we know the base address (where the array starts in memory) and the size of each data item.