On a PRO, the MFM hard drive is ID'd by the number of heads and number of cylinders. If you look at, for example, DW.MAC on a RT-11 distribution kit, you'll find the table quite easily. You can add your own devices to the table - just keep in mind that it has to be in ascending order by heads, and then ascending order by cylinders. OK, the above is a bit of an oversimplification - if the drive in question happens to be a RD50, the drive might be damaged by the seek test that counts the number of cylinders. So RD50's are identified by a bit in the status/init register, and not by the seek test. The PRO's MFM controller only allows 3 bits for the head ID and 10 bits for the cylinder ID, so you can only use drives up to 8 heads and 1024 cylinders (aka the RD53). -- Tim Shoppa Email: shoppa(a)trailing-edge.com Trailing Edge Technology WWW: http://www.trailing-edge.com/ 7328 Bradley Blvd Voice: 301-767-5917 Bethesda, MD, USA 20817 Fax: 301-767-5927