We consider the problem of scheduling tasks requiring certain processi
ng times on one machine so that the busy time of the machine is maximi
zed. The problem is to find a probabilistic online algorithm with reas
onable worst case performance ratio. We answer an open problem of Lipt
on and Tompkins concerning the best possible ratio that can be achieve
d. Furthermore, we extend their results to an m-machine analogue. Fina
lly, a variant of the problem is analyzed, in which the machine is pro
vided with a buffer to store one job.