The maximum size of possible addressable memories

The define memory directive defines a memory space with a given size, which is the maximum possible amount of addressable memory, not necessarily physically available. See define memory directive.

Available physical memory

The define region directive defines a region in the available memories in which specific sections of application code and sections of application data can be placed. You can also use this directive to declare whether a region contains RAM or ROM memory. This is primarily useful when building for a traditional ROM system. See define region directive.

A region consists of one or several memory ranges. A range is a continuous sequence of bytes in a memory and several ranges can be expressed by using region expressions. See Region expression.