RL02K Pack Reliability/Characteristics

Pete Turnbull pete at dunnington.plus.com
Wed Apr 1 05:01:56 CDT 2015

On 01/04/2015 07:09, Christopher Parish wrote:
> On 01/04/2015 04:58, Johnny Billquist wrote:
>> 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...

> 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.

That doesn't necessarily mean they're perfectly aligned, because the 
servo will correct for small differences.  Switching heads and still 
being on the same track is what's supposed to happen even if the heads 
are almost half a track off.  You'd need to check with a scope to be sure.

> A normal single track seek on my drive takes ~12ms.

That's about right, if a shade fast.  "Less than 17ms" is nominal; mine 
take about 14-15ms.  Have you tried setting up an oscillating seek over 
longer distances?  It should be about 55ms for 170 tracks, and a little 
less than 100ms (about 95ms on mine) for 511 tracks.

> 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.

That's similar to what mine did with a faulty DLM, although I don't know 
that it made a difference whether the destination was an odd or even 
track.  I did notice that sometimes the heads would move beyond track 
511 into the guard area in the centre of the disk, and the times went up 
from ~95ms to around 110ms or more.  It no longer does that, of course.


Pete Turnbull

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