IDATA is a physical attribute of the hardware - it exists whatever Memory Model you choose!

The Memory Model is simply a directive to the Compiler to tell it which memory space to use by default when you don't explicitly state one.

You can always add an explicit memory space qualifier to any variable definition!

You really need to take the time to study the Keil Documentation to understand these issues:

Memory Areas: http://www.keil.com/support/m...mareas.htm

Memory Models: http://www.keil.com/support/m...models.htm

Memory Types: http://www.keil.com/support/m...mtypes.htm

Note that Keil doesn't have a Memory model that uses IDATA (the Compact model uses PDATA).