That's not entirely correct. You certainly can have code in external RAM if you wire the PSEN and RD pins correctly. Some derivatives also do allow code to be executed from on-chip MOVX RAM. The TI MSC1210 comes to mind since it has 1k of MOVX memory on-chip which can also be used to execute code (pretty nifty for dynamic code purposes). And that same TI part allows the available flash memory to be partitioned between code flash memory and data flash memory.

Of course you're right that the traditional 8051 is a Harvard device and that most 8051 programs aren't executed from RAM. But the above blanket statement does need these qualifiers and the original question was not without merit (though I'm sure it could be answered by reading the datasheet).

Regards,
Craig Steiner