It is important for coalescing to be able to find the previous and next blocks when given only a pointer (the argument passed to free) to an allocated block.

But we already have overhead of 8 bytes in each allocated block for the header and footer, which the user can't (at least should NOT) use.

How do we find if the previous block is free?

How do we find the size of the previous block?

How do we find the beginning address of the previous block?