It is not that it is just ‘less sensitive’. I’m really stretching my memory from the research I did on the subject here but as I recall the composition of the coating of the disk is different (something like the particle size of the ferrous material being smaller). To flip the domain on this new HD coating requires a stronger magnetic field. The DD drive cannot output a strong enough magnetic field to properly magnetize the new HD coating.
Jeff Birt From: M100 <m100-boun...@lists.bitchin100.com> On Behalf Of Brian White Sent: Saturday, March 20, 2021 8:49 AM To: m...@bitchin100.com Subject: Re: [M100] TPDD service manual Not that it changes anything, but I thought the problem with the density difference was that the lower density drive would put out a stronger signal needed for the less sensitive media, and so the problem with using hd media in a dd drive would be that the dd drive would overdrive the media making a distorted signal? Is it actually the opposite, that the way they achieved higher density is by using less sensitive media driven by a stonger head? On Sat, Mar 20, 2021, 8:35 AM Jeffrey Birt <bir...@soigeneris.com <mailto:bir...@soigeneris.com> > wrote: Oh, sorry I misread what you wrote. But to your point, that could be done. I use a SuperCard Pro to image floppies which is just a PIC uC with supporting HW and some spiffy firmware/software. It can image TPDD1/2 disks easily using a standard 3.5” 1.44MB drive. The software does know how to interpret the data, it is just a flux map. The .SCP format is well documented though so one could figure out how to recreate the disk file structure from it. There is a similar device called the Flux Engine that has already done the file system decoding and can image/interpret TPDD disks using a standard 3.5” 1.44MB drive. Jeff Birt From: M100 <m100-boun...@lists.bitchin100.com <mailto:m100-boun...@lists.bitchin100.com> > On Behalf Of Stephen Adolph Sent: Saturday, March 20, 2021 7:28 AM To: m...@bitchin100.com <mailto:m...@bitchin100.com> Subject: Re: [M100] TPDD service manual not exactly the point I was trying to make. pretty clearly a TPDD1 cannot use an HD floppy. but a small microcontroller that speaks TPDD protocol and has integrated FDC function could interface with a modern FDD. ..steve On Sat, Mar 20, 2021 at 8:20 AM Jeffrey Birt <bir...@soigeneris.com <mailto:bir...@soigeneris.com> > wrote: High density disks, both 3.5 and 5.25, require a much higher flux level to write. A system designed for DD disks will not be able to write to them reliably. Some folks have tried HD 3.5” disks in an Amiga or Mac for example only to find that it reads for a while but after a few weeks or months it no longer does. You can generally write to lower density disks with a HD drive. The exception being that it is best to write 360K 5.25”disks with a 360K drive as the head on these drives was physically larger and the narrower track written by a higher density drive may not work well on all 360K drives. My take on the TPDD is that it was designed to be cheap (simple) and portable. Thus, they used a simple 8-bit micro to control everything and not one of the floppy disc controller ASICs that were available at that time. But, they wound up with something that would run on AA batteries and use standard media at the time even if the storage capacity was limited. Jeff Birt From: M100 <m100-boun...@lists.bitchin100.com <mailto:m100-boun...@lists.bitchin100.com> > On Behalf Of Stephen Adolph Sent: Saturday, March 20, 2021 5:59 AM To: m...@bitchin100.com <mailto:m...@bitchin100.com> Subject: Re: [M100] TPDD service manual this is quite interesting, and nice detective work. It would seem like an interesting use case here could be to modify this firmware to make it target a standard 1.44MB floppy disk drive. Maybe it would seem a bit backwards because SD cards are more mainstream, but still interesting to think about. I see you have the disassembly in place.