myUnallocatedSpaceDescriptor.NumberofAllocationDescriptors = 1;
myUnallocatedSpaceDescriptor.AllocationDescriptors = new Extend_ad[1];
// unallocated space #1
// TODO: extend method for describing more than one unallocated space area
myUnallocatedSpaceDescriptor.AllocationDescriptors[0] = new Extend_ad();
myUnallocatedSpaceDescriptor.AllocationDescriptors[0].loc = unallocatedSpaceStartBlock;
myUnallocatedSpaceDescriptor.AllocationDescriptors[0].len =
(unallocatedSpaceEndBlock - unallocatedSpaceStartBlock) * blockSize;
myRandomAccessFile.seek(targetBlock * blockSize);