Physical and virtual memory
Memory devices in computers can be categorized as random-access memory (RAM), which can be read from and written to at will, and read-only memory (ROM), which, as the name indicates, can be read but not written. Some types of memory devices, such as flash memory and electrically erasable programmable read-only memory (EEPROM), inhabit a middle ground, where the data content of the devices can be changed, just not as easily, or as quickly, or updated such a large number of times, as standard RAM.
Memory devices within a computer must be configured to ensure that each device occupies a unique span of the system address space, enabling the processor to access each of possibly several RAM and ROM devices by setting its address lines appropriately. Modern computer systems generally perform this address space allocation automatically, based on the slot a memory device occupies.
Software running on early computer systems, and on the less-sophisticated computers...
