The magnetic coercivity on HD disks is different than on regular disks. It requires more energy to lay down the tracks. If you start with a blank HD disk rather than a pre-formatted disk then you have a better chance. That's because once the HD tracks are laid down, you need to erase them for your new format. If your drive doesn't have enough energy to completely erase the existing track, it wont work. 720k disks have a lower coercivity and therefore work with either a 720k or 1.44mb drive. A 1.44 drive has a sensor for the open hole and when it sees that hole, it will use a higher level of write energy to properly work with the media. When that hole is covered, it will use a lower level which is what the 720k media is looking for. Though I do remember that formatting a 720k disk in a 1.44mb drive didn't always work when going back to a 720k drive.
Not sure about the Coco drive, but my TPDD2 does not work reliably with HD disks. I have only been able to format one properly and it had data failure shortly after. Kurt On Sun, Mar 24, 2019, at 6:32 PM, Stephen Adolph wrote: > interestingly, > > Yes, if I take an HD disk, and tape over the hole to make it appear to be a > DD disk, then it works. > > But why? > > the floppy is capable of both formats... > > On Sun, Mar 24, 2019 at 7:39 PM Mike Stein <mhs.st...@gmail.com> wrote: >> __ >> Have you tried closing the HD sense hole with a piece of tape or similar? >>> ----- Original Message ----- >>> *From:* Stephen Adolph <mailto:twospru...@gmail.com> >>> *To:* m...@bitchin100.com >>> *Sent:* Sunday, March 24, 2019 6:08 PM >>> *Subject:* Re: [M100] question regarding floppy disks. >>> >>> the Coco is using it's standard controller >>> >>> When issuing the DSKINI 0 command the coco tries to format for 180kB. >>> >>> The combination of >>> (Coco, std controller, PC 1.44MB drive + a 720kB dd floppy) works >>> >>> whereas >>> (Coco, std controller, PC 1.44MB drive + a 1.44MBB hd floppy) does not work >>> >>> this is something I don't understand! >>> >>> >>> >>> On Sun, Mar 24, 2019 at 5:42 PM Gregory McGill <arcadeshop...@gmail.com> >>> wrote: >>>> likely the floppy controller doesn't support 80 tracks or high density.. >>>> most of the controllers of the era are ds/sd 40 track or dsdd 40 track.. >>>> are you able to format 720k? ds/dd 80 track? >>>> >>>> Greg >>>> >>>> On Sun, Mar 24, 2019 at 2:38 PM Stephen Adolph <twospru...@gmail.com> >>>> wrote: >>>>> I'll start by saying this isn't an M100 or TPDD discussion, but just >>>>> looking to understand something. >>>>> >>>>> I have a Tandy Coco3 with a 3.5 inch floppy drive. The drive is a >>>>> standard PC drive and it is working well. >>>>> >>>>> Seems though that I cannot use 1.44 MB floppies in that drive. They don't >>>>> seem to want to format. >>>>> >>>>> I really don't understand where the problem could be. >>>>> - the drive and the floppy are compatible >>>>> - the disk is known good and formats at 1.44MB in a PC >>>>> - if it can support 135 TPI, why can't it support 35 TPI? >>>>> >>>>> Does anyone know what's going on? >>>>> >>>>> thx >>>>> Steve
