Date   : Wed, 10 Aug 2011 14:42:25 GMT
From   : jgh@... (J.G.Harston)
Subject: Risc PC (Was 'Minitel in France')

Theo Markettos wrote:
> Furthermore, the 26 bit memory map limits the
> amount of physical RAM to 16MB.

The CPU's address bus doesn't limit the amount of physical memory,
only the amount of memory the CPU can see at one time.

The 6502 only has a 16-bit address bus, but the BBC has 20 bits of
memory (16 sideways banks at &8000-&BFFF).

The Z80 only has a 16-bit address bus, but the Spectrum 128 has 19
bits of memory (8 sideways banks at &C000-&FFFF).

The Z80 can access 1M of memory with a memory manager such as this
one: http://mdfs.net/Info/Comp/Z80/Circuits/1MbMem.gif

The amount of physical memory accessible is limited by the number
of address lines on the outgoing side of the memory management
system, not the CPU.

-- 
J.G.Harston - jgh@...      - mdfs.net/jgh