TESTFDC usage

The commonly found 5.25" drives are: A: Single-Sided, 35 track, 48 tpi (original SA400) B: Single-Sided, 40 track, 48 tpi (SA400L and others) C: Double-sided, 40 track, 48 tpi (SA450, TM-100-2, TEAC55B, etc.) D: Double-sided, 80 track, 96 tpi (SA460, TM-100-4 TEAC55F, etc.) E: Double-sided, 80 track, 96 tpi, High Density (TEAC55G, Pan JU-475 etc.) Less common, but I've run into a couple are: F: Single-Sided, 80 track, 96 tpi (can't think of any models) Still (much) less common are: G: Double-Sided, 77 track, 100tpi (TM-100-4M) A, B and C are compatible within the areas that they overlap, ie: C can read/write B and A, and B can read/write A D and F are compitible within the areas that they overlap (ie, side1), and can be "mostly" compatible with A, B and C within the areas that they overlap by double-stepping (ie: the even 96tpi tracks line up with the 48tpi drive tracks. There is an issue with the head being "thinner" which can cause some incompatibilities when disks are written on a 48 tpi drive, then re-written on a 96tpi drive, and then read on a 48 tpi drive - this is due to remanents of the original pattern remaining at the edges after a thinner track is laid down by the 96tpi drive head causing confusion when it's read back with the wider 48tpi drive head. E can be compatible with D and F within the areas that they overlap provided it is run at low-density and 300rpm, or 360rpm with a modified data rate. It can also be compatible with A, B and C by the use of double stepping. G is incompatible with all others, because the 100 tpi tracks have a different spacing and therefore you cannot position the head over all tracks of a 48 or 96 tpi written diskette. Make sense? Dave -- dave06a (at) Dave Dunfield dunfield (dot) Firmware development services & tools: www.dunfield.com com Collector of vintage computing equipment: http://www.classiccmp.org/dunfield/index.html