According to the RL tech manual... Disk Address Register During Read or Write Data Command --- ... Bit 6 Head Select Indicates which head (disk surface) is to be selected. A 1 indicates the lower head, a 0 the upper head. The correct track (_head_ and cylinder) must have been previously selected by a seek. I've just looked in the RL01 printset (the RL02 must be similar), and the head select signal comes from a register that only seems to be loaded on a seek command. So you _do_ need to do a 'seek' to change heads. Hope that helps -tony