> ...similar devices to _read_ disks at a magnetic level...
It's not, though. It's reading the disk after the drive's analog-to-digital converter has had its way with the analog flux transitions coming off the head. There's auto gain control circuits in there, and a pre-amplifier, and finally the ADC. Greaseweazel and its ilk are closer to the flux than just reading the disk in the conventional manner but it isn't actually sampling the raw flux reversals.
The Domesday Duplicator is closer to what I'm taking about. You can do software-defined manipulation of the sampled analog signal. In its case, it's a software-defined laserdisk player. (One could do the same w/ VHS, for example.)
I'll try to dig up a good Vintage Computer Festival talk from a guy who was recovering analog signals from old tapes and reconstructing the data by building a software-defined "tape drive" and using signal processing algorithms that would be applicable in the software-defined radio domain.
It occurs to me that such an analog duplicator wouldn't need fancy FPGAs and high-speed digital signal processing that didn't exist back then. It would "just" need very clean analog circuitry and decent motor control.
It looks like the Applesauce[0] project does what I'm talking about. It's sampling analog signals from the drive, rather than the output of an old ADC. Very cool.
Yeah it'd be interesting to have a full analog floppy reader/writer for data recovery. Might as well make it fast enough to read early hard drives (at least through early IDE) too.
Probably could stuff quite a bit more data using today's methods on a disk, too, even though in the scheme of things it'd be pretty pointless... but why should that stop someone? ;)
It's not, though. It's reading the disk after the drive's analog-to-digital converter has had its way with the analog flux transitions coming off the head. There's auto gain control circuits in there, and a pre-amplifier, and finally the ADC. Greaseweazel and its ilk are closer to the flux than just reading the disk in the conventional manner but it isn't actually sampling the raw flux reversals.
The Domesday Duplicator is closer to what I'm taking about. You can do software-defined manipulation of the sampled analog signal. In its case, it's a software-defined laserdisk player. (One could do the same w/ VHS, for example.)
I'll try to dig up a good Vintage Computer Festival talk from a guy who was recovering analog signals from old tapes and reconstructing the data by building a software-defined "tape drive" and using signal processing algorithms that would be applicable in the software-defined radio domain.
It occurs to me that such an analog duplicator wouldn't need fancy FPGAs and high-speed digital signal processing that didn't exist back then. It would "just" need very clean analog circuitry and decent motor control.
Edit:
Here we go. Video of the talk: https://www.youtube.com/watch?v=sKvwjYwvN2U
A comment I made about it: https://news.ycombinator.com/item?id=31939703
Edit 2:
It looks like the Applesauce[0] project does what I'm talking about. It's sampling analog signals from the drive, rather than the output of an old ADC. Very cool.
[0] https://wiki.reactivemicro.com/Applesauce
There's some discussion here[1] about analog recovery of floppy data and some past discussion[2] from HN.
[1] https://scarybeastsecurity.blogspot.com/2021/05/recovering-l...
[2] https://news.ycombinator.com/item?id=27187435