Alex is right, Murugan (sorry) is wrong. Go to http://www-us.semiconductors.philips.com/handbook/...us_66.html and download the 80C51_fam... documents. Page 2 of the programmers guide has a nice picture showing how the '51/52 ahndle memory. The chips with more than 256 bytes of RAM have "some of the external RAM internal" this does not make sense, I know, however the '51 has evolved and this is the way it was done. So, to access the internal RAM you have the "standard '52 internal ram (128 bytes direct starting at address 0, 128 bytes indirect starting at address 80h, and internal XRAM starting at address 0.

Whenever I have had to explain this face to face, its been difficult, so if you do not understand this, just accept IT IS INTERNAL XRAM.
don't forget: Have fun
Erik

PS: This is not a compiler issue, any compiler I know can handle the full memory.