Old (big) mag cards?

[blackjetrock]

(07-05-2023 03:26 PM)johnb Wrote:  Just out of pure curiosity, I'm guessing Hi-Co and Lo-Co are abbreviations for "High Coercivity" and "Low Coercivity"?

Educate me! Why two different kinds of media? Advantages / disadvantages, and so on...

Yes, high coercivity and low coercivity.

Coercivity is a measure of how hard it is to magnetise the material. It's what H is needed to magnetise, on the B-H curve. If you want to make something that isn't going to be re-recorded like an ID badge then you'd use Hi-Co as it will be recorded in a special Hi-Co writer. It is then more robust to stray magnetic fields. Lo-co material is used when you will be re-recording data, like calculator storage cards. As the H of the BH is generated by electric current, hi-co writers need more power than lo-co to reach the required H. So in battery powered equipment you'd use lo-co to reduce the power requirement.

Andrew