Reading out of a NOR Flash is similar to reading out of a random-access memory, provided the address and data bus are mapped correctly. Because of this, most microprocessors can use NOR Flash memory as execute-in-place memory, meaning that programs stored in NOR Flash can be executed directly without the need to copy them into RAM. That is not the case for NAND Flash memory in which programs cannot be executed directly; instead, code shadowing must be performed. Microchip’s boot ROM makes it possible to boot from one of these NAND Flash based memories which do not require an external NOR Flash.