🚀 go-pugleaf

:> The A2090 supports only 8 heads, thus is ST-506 compatible.
:> 
:> The Seagate ST-251 drive has 6 heads and will function with either an ST-506
:> or ST-412 compatible controller.
:
George Robbins responds:
:That's more reasonable.  The 8+ head drives reassign one of the control
:signals for the 3'rd head select line.  Traditionally, this has only
:occurred on the high-capacity/high-doller drives by Maxtor and others,
:but these drives are now showing up on the surplus market for ~$1K...

	As far as the buffered seeking goes, you *can* use unbuffered seeks
on an ST-412 drive but it is incredibly slow.  I don't know what the A2090
does... I assume it supports buffered seeks.  ST-412 Buffered seeking is
nice because it allows the drive firmware to execute high speed seeks.

	Heads:  ST-506 supports 8 heads (3 select lines).  ST-412 supports
16 heads (4 select lines).  Specifically, a line associated with write
precompensation was turned into a fourth select line  (I think it's the
reduced-write-current line).  Write precomp is almost never used anymore on
newer drives.  Only 1 or 2 of the dozen or so Seagate drives uses it.

	In anycase, four select lines means 16 heads.  It is utterly trivial
to support this expansion in controllers since none of these drives support
parallel reads... you select one head at a time.  I very strongly suggest
that you guys at C-A implement the line in the A2090.

	The seagate 4096 (80 MB) drive has 9 heads.  *Most* serious users
are going for 80MB+ drives these days.

					-Matt