There is no such a thing as a Flat RM. "Unreal" flat -- is. Definitely, what do you mean of the "flat real"?

Segmentation is of no use to protect processes from each other without page faults. sic.

OK, spread it lightly...

You have 65535 selectors (most of them of no use, and 8k*2 descriptors, too). Without paging, you're limited to 4GB.

hello everybody:

paging has one avantage against a flat adress space. A modern memory managment mechanism (slab allocator or something similar) can eleminate fragmentation though remapping of splitting areas into a linear adress space. These reduce the complexibility to handle memory areas of different size and position at cost of the mean performance for memory accesses (because the fast change of mapped adresses results in increasing page faults).