Back in the olden days, like 1995, classmates used to buy cheaper DD floppies and drill holes into them to use them as HD floppies (the 3 1/2 floppy had a hole in one of the corners to allow the drive to distinguish between DD and HD drives).

I didn't do that because I feared data loss, yet in a recent discussion, people claimed that this was not much of an issue. Which led me to reconsider; I assume that manufacturers switched to producing only HD media, simply putting some of them into DD casings, possibly those who didn't pass as well in QC. From an economic perspective, it would make perfect sense: rather than having to manufacture two different media, the manufacturer could produce only one. The cost difference between DD or HD media would vanish over time and far outweigh the expenses saved by having to maintain only one production line.

However, someone else claimed that there is a substantial physical difference between DD and HD media, which is substantial enough to necessitate the production of "true" DD media. Therefore, people "faking" HD disks would really risk data loss.

Is he right or not?


Yes, there's a substantial difference between HD and DD media.

Magnetic material has a property called coercivity that is measured in oersteds. The coercivity of the magnetic coating is related to the field strength necessary to change the magnetization when writing data.

For 3.5 inch floppy disks, DD media has 665 oersteds, while HD media has 720 oersteds. [1] So when using the wrong media, writing data will either use too little or too much field strength, resulting in "weak" bits that are difficult to read and can produce errors, and also reduce the lifetime of data.

The same kind of difference (but with a different numbers) exists between HD and DD media for 5.25" floppies.

[1] http://www.retrotechnology.com/herbs_stuff/drive.html

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.