From: allisonp(a)world.std.com (Allison J Parent) The number of tracks is different, with more on the TK70 than on the TK50 (not surprisingly). When a TK70 drive tries to read a TK50 tape, it's easy enough to center a smaller (TK70) read head on a larger (TK50) track. It is far more difficult (that is, practically impossible) for the smaller write head to write a track which covers the larger track well enough to satisfy the larger read head. _This_ is why a TK70 drive can not write a tape which can be read by a TK50 drive. The magnetic properties of the tapes may or may not be different. My experience suggests that they're close enough. (Of course, also I've used HD floppies as DD by taping over the hole, again, with no problems. Please, let's not start that discussion here.) Regardless, it's the difference in track configuration which is the fundamental source of the problem. The same argument applies similarly to QIC tape drives of various densities. If anyone actually _knows_ about the magnetic properties of the two types of tapes, I'd be pleased to learn of the differences, if any. I could live happliy without additional uninformed speculation. ------------------------------------------------------------------------ Steven M. Schweda (+1) 651-645-9249 (voice, home) 1630 Marshall Avenue #8 (+1) 612-754-2636 (voice, work) Saint Paul MN 55104-6225 (+1) 612-754-6302 (facsimile, work) sms(a)antinode.org sms(a)provis.com (work)