^^^^^^ *A* pair? It's a fixed head disk of 64 tracks, so I'd expect 64 such heads! RS03: 64 tracks, 64 sectors/track, 64 words (128 bytes) per sector. RS04: 64 tracks, 64 sectors/track, 128 words (256 bytes) per sector. An RS03 actually has 4 spare tracks and a timing track, while the RS04 has 8 spare tracks and a timing track, with (of course) a set of heads for each track. And, of course, a zero millisecond seek time. -- 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