RL02K Pack Reliability/Characteristics

Christopher Parish christopher.parish at parishcomputers.com
Wed Apr 1 01:09:35 CDT 2015

> This sounds strange. Are you sure you are not just fiddling with the
> head here? A head switch will taste like a seek, but it might actually
> not move you as you would expect...
>        Johnny

The head bit is not adjacent to the cylinder offset field in the command word, and I've verified with the logic analyzer that my intended commands are being sent.  Actually, it's ironic because the head alignment on my drive is near perfect.  I can switch heads and I am on the same track, opposite side, every time.

Now I'm almost certain this seeking problem has something to do with the logic on the drive because so far, the drive only ever mis-seeks when trying to land on an odd numbered track.  The controller re-issues the seek, but there's a time penalty.  

A normal single track seek on my drive takes ~12ms.  Most bad seeks to odd numbered tracks tend to take me an additional track beyond what I wanted, requiring another ~12ms seek to get back on track.  Not that performance is a key factor here, but I'd like to understand why this is happening.


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