Diffrence between external and internal design

External Design
External design is also called basic design or external design, and generally up to external design is included in the upstream process.
The basic design of the system is performed based on the functions, performance, and constraints determined in the requirements definition. Basically, the specifications for the user are designed, such as determining the specifications of the interface part that can be seen by the user such as the operation screen, operation method, data output etc., designing security and operation rules, schedule and expenses of system development, etc. It is external design to do.

Internal Design
The internal design is based on the external design to design details that are difficult for the user to see, such as the operation and functions inside the system and physical data. Although this is a process between external design and detailed design to performed afterward, it is sometimes treated as the same process as detailed design because it is specialized for internal system. Divide program functions into single units and design physical data and input / output to be used there. The role of internal design is to make the result of external design easy to program.

I would like to accumulate more know-how and knowledge on internal design.