Every CPU from the 386 to the latest Pentium and Athlon processors has used a 32-bit architecture, which means that the internal registers of the CPU are 32 bits wide. In other words, 32 bits of data are the most the CPU can handle on a single instruction cycle, and a block of data that size is considered to be one ‘word’ of data for that CPU. A ‘word’ not only determines the size of a program instruction, but also the maximum size of a RAM location that the CPU can address. This turns out to be 4,294,967,295, which means that a 32-bit architecture can use a maximum of 4 GB of RAM. By comparison, a 64-bit architecture can address 16 exabytes (16 billion GB) of RAM.