With an address width of 20 bits, as with the first central processing units( CPU) of the 80x86 series, an addressing range of 1 million addresses results, which corresponds to a memory area of 1 megabyte( MB). With an address width of 24 bits, the addressing range increases to 16 million, respectively 16 MB memory, and with a width of 32 bits, as with the Pentium Pro, 4 * 10^9 addresses can be addressed. This corresponds to a memory volume of 4 gigabytes( GB) of memory. And with a 64 bit address bus width, there are over 10^18 addressing possibilities.