  Contrary to a widely accepted view the phase diagrams of
La$_{2-x}$Sr$_x$CuO$_4$ and YBa$_2$Cu$_3$O$\rm_{6+y}$, in spite of similarities
are remarkably different. Both the electric conduction properties and the
commensurate/incommensurate spin ordering properties differ dramatically. It is
argued that the role of disorder in YBCO is insignificant while the bilayer
structure is crucial. On the other hand in LSCO the intrinsic disorder to a
large extent drives the properties of the system. The developed approach
explains the low-temperature magnetic properties of the systems. The most
important point is the difference with respect to the incommensurate spin
ordering, including the difference in the incommensurate pitches. The present
analysis demonstrates that the superconductivity is intimately related to the
incommensurate spin ordering.
