Stephane, you need to go back to the Manual and read carefully about the meaning of the Memory Model, and Keil's 8051-specific extensions for defining variables to use the different memory spaces - DATA, IDATA, PDATA, XDATA or CODE.

Basically, Keil provides keyword extensions which allow you to explicitly specify which memory space is to be used for a variable; if you don't take advantage of this, the default memory space is defined implicitly by the Memory Model; viz:
* Small - variables in DATA;
* Compact - variables in PDATA;
* Large - variables in XDATA