Firt off that is for for up to 65536 sectors (per track). As that directly maps to only sectors on a track and only for 128byte logical sectors. (typically it's less than 64 for most disk drives) It would be that if for only one thing. The math is not way. The calulation is 65536 sectors total or 65536*128 or 8516608 (8mb). It's really a result that all math truncates to 16bits. there are BDOSs that fix this (P2DOS, Suprbdos, Novados, ZRdos...) and can do the full 2Gb. Define pointless.. The problem is if your using a LBA HD or CF that has more than 8MB then you have to partition the drive. Also for LBA addressing there are some track and sector tricks that can be applied as well for deblocking. You might. It allows up to 16bit values for both track and sector. While floppies never use more than byte values the parameters passed to the BIOS is a word and it's at your choice to truncate to byte. Caveat: For floppies and smaller hard disks they are CHS, usually cylinders needs a byte for floppy but hard disks it may have more than 256 cylinders. Both however rarely have more than 64 logical sectors per track so a byte works. The gotcga is devices like Ramdisks, CF and larger IDE drives are or can be LBA where it's easier to look at it as 1 track of 65536 sectors or 65536 tracks of one sector or anything that multiples out to 65536! Where the byte/word thing is important is this case: Hard disk organized as 16spt (assume they are 128 byte sectors which rarely happens) and 8192 tracks for 16mb. Thats a total of 131072 sectors. So to use it all you partition it in the bios as two drives and one has an offset(reseverd tracks) of half the total tracks or 4097. That means the parameter for tracks passed will be a word as you need at least 13bits. CP/M does handle that correctly. It's gets discussed but not often and it's straight forward and not obvious. The CP/M alteration guide is plain poor on why or how. the only book that explains this reasonably and you have to read the whole book to get all the bits is Andy Johnson-Laird, The Programers CP/M Handbook. I have done enough things with CP/M and it's bios to have the need to understand it and that books was both best and good reference. Prior to that I had to infer, guess and test to see what was really happening. As a result when I do a bios SETTRACK, and SECSEC stores a word value and else where I can then selectivly chose to use a byte or word. Also SECTRAN (AKA skew) is a allways NUL routine in my BIOS as it's useless when drives that have sectors larger than 128 bytes. For hard disks and CF/IDE types it's never used as they are too fast. If I need Sectran functionality I do it at the device level rather than have BDOS do the work. You may use it if you wish and it applies well for any disk that is SD especially for 8"SSSD. Hope that helps. Allison