All these three mapping methods are explained with the help of an example.

Consider a cache of 4096 (4K) words with a block size of 32 words. Therefore, the cache is organized as 128 blocks. For 4K words, required address lines are 12 bits. To select one of the block out of 128 blocks, we need 7 bits of address lines and to select one word out of 32 words, we need 5 bits of address lines. So the total 12 bits of address is divided for two groups, lower 5 bits are used to select a word within a block, and higher 7 bits of address are used to select any block of cache memory.

Let us consider a main memory system consisting 64K words. The size of address bus is 16 bits. Since the block size of cache is 32 words, so the main memory is also organized as block size of 32 words. Therefore, the total number of blocks in main memory is 2048 (2K x 32 words = 64K words). To identify any one block of 2K blocks, we need 11 address lines. Out of 16 address lines of main memory, lower 5 bits are used to select a word within a block and higher 11 bits are used to select a block out of 2048 blocks.

Number of blocks in cache memory is 128 and number of blocks in main memory is 2048, so at any instant of time only 128 blocks out of 2048 blocks can reside in cache menory. Therefore, we need mapping function to put a particular block of main memory into appropriate block of cache memory.