The Amstrad CPC had 64K or 128K of RAM + 32K of ROM (in a total addressable space of 64K) using "RAM banking". The Amstrad PCW was the same but with even more RAM (up to 512K). This worked very differently from what we now think of as virtual memory.
On the CPC it worked as follows: There were two 16K ROMs, located at 0-16K and 48K-64K. The 16K-48K middle area contained 32K of fixed RAM.
The upper and lower ROM areas were shadowed by RAM. By writing to an IO port you could switch in either the ROM or a 16K bank of RAM individually into each of those two 16K areas. There was an elaborate system of trampolines to allow the ROM functions to be called, or for the ROMs to read/write to the bank of RAM "hidden" under them.
