For pure Harvard machines, there is an address "zero" in instruction space that refers to an instruction storage location and a separate address "zero" in data space that refers to a distinct data storage location. By contrast, von Neumann and split-cache modified Harvard machines store both instructions and data in a single address space, so address "zero" refers to only one location and whether the binary pattern in that location is interpreted as an instruction or data is defined by how the program is written. However, just like pure Harvard machines, instruction-memory-as-data modified Harvard machines have separate address spaces, so have separate addresses "zero" for instruction and data space, so this does not distinguish that type of modified Harvard machines from pure Harvard machines.