A method and apparatus is provided to enable provision of requested data
within two clock cycles when performing a swap operation between an
accessible memory cell and a background memory in a computer. In a first
clock cycle, memory addresses to be used in the swap operation are
decoded. In a high phase of a second clock cycle, requested data is
restored from the background memory to an accessible memory cell. Because
the data previously stored in the accessible memory cell is duplicated in
a shadow memory cell, the restoration of data to the accessible memory
cell is performed without data loss. In a low phase of the second clock
cycle, the requested data is available for reading. During a third cycle,
data is saved from the shadow memory cell to the background memory, and
the shadow memory cell is made consistent with the accessible memory
cell.