list = []
for si in context.portal_catalog(url_string=context.getUrlString(), portal_type='Software Installation', validation_state='validated'):
  computer = si.getAggregateValue()
  if si.getSlapState() == 'start_requested' and \
      not computer.Computer_getSoftwareReleaseUsage(context.getUid()) \
      and computer.getValidationState() == 'validated':
    list.append(computer)

return list
