On Sun, 08 Mar 2020 17:11:57 -0000
Daniel James  wrote:

> By the time the IBM PC appeared most CP/M-80 machines I was seeing
> wrote either 10 512-byte or 5 1024-byte sectors on a track on a 5.25"
> floppy -- making 400kB of data in all. The mostly used WD controller
> chips that allowed that. The floppy controller in the PC writes too
> much lead data on each track to achieve that, so the best it can do is
> 9 sectors of 512 bytes -- giving 360k (DOS originally wrote only 8
> sectors to keep the addressing simple(r), giving 320k in all).

 Yep I recall wondering at the time why they set up 400K drives so
badly. I did encounter a claim that it was for reliability.

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