ZX Spectrum disk interfaces

[Liam Proven]

A question born only of idle curiosity.

In thge 1980s, I bought an MGT +D disk interface for the Sinclair ZX Spectrum:

https://en.wikipedia.org/wiki/%2BD

In the end, I traded mine in for its upmarket cousin, the DISCiPLE:

https://en.wikipedia.org/wiki/DISCiPLE

(I link to WP as I originally wrote those articles, IIRC. :-) )

I have noticed that multiple people have now cloned the +D:

http://sintech-shop.co.uk/sinclair/-d-disk-interface-clone/a-6196/

http://www.rwapsoftware.co.uk/spectrum/spectrum_storage.html#plusd

But this post, from FB, claims that the Beta Disk interface can handle
high-density drives, giving 1.5MB per disk:

https://www.facebook.com/groups/speccy4ever/permalink/1237322356346334/

Given that HD floppies and drives are far more readily-available than
DD these days, how come most 8-bit interfaces can only handle DD? Is
it purely a data rate issue?


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