If all clients are assigned to one group, GSS reduces to SCAN,

and if all clients are assigned to separate groups, GSS

effectively becomes round-robin scheduling. The service order

within one group is not fixed, and a stream may in fact be

first in one cycle while last in the next. This variation has

to be masked by extra buffering but whereas SCAN requires

buffer space for all streams, GSS can reuse the buffer for

each group and effect a trade-off between seek optimisation

and buffer requirements.