At 04:47 PM 2/5/2013, Bob Vines wrote: There's no format difference. There's a bit called the "mode" bit (software selected) which selects 12-bit mode or 8 bit mode for the RL8A. In 12-bit mode, a sector contains 128 12-bit words or 256 8-bit bytes - 64 bytes are wasted in 12-bit mode. (Also, with 12-bit mode, you can't DMA more than one sector at a time.) I don't know for sure, but I'll bet that OS/8 runs in 12-bit mode. You *do* have to run a magic formatter program on the '8 that fixes up the bad block map into where OS/8 expects it. As far as the jumper Charles is referring to - there's a pair of jumpers on the RL8A that need to be configured. W8 is installed to support the RL02 (W8), W9 installed for the RL01. Only one of those jumpers are installed at a time. If the zero drive is working, W8 is installed. What this does (when W9 is installed) is to limit the track delta register to the RL01 size. -Rick