[robespierre]

The geometry data for the drive is

Code:

MK156FB     SCSI          10 heads        830 cylinders        35 sectors         0 Write-Precomp    830 Landing-Zone     145MB Capacity

The operation manual for the related MK156FA (an ESDI drive) is here. Of note:

Use of a center stack servo system improves head positioning accuracy across the full environmental operating range and allows servo writing to be performed with the disk stack mounted in the drive.

So it has a dedicated servo surface on an inner platter.

My 4D/70G was slightly different: the power inlet was a Hubbell twist-lock, not an IEC connector, the base compartment of the side tower had space for a tape drive, and there was a DC-37 port on the back for some unknown purpose (ESDI? Parallel?)