dillon@CORY.BERKELEY.EDU (Matt Dillon) (09/25/88)
:> 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
dale@boing.UUCP (Dale Luck) (09/28/88)
In article <8809250346.AA23887@cory.Berkeley.EDU> dillon@CORY.BERKELEY.EDU (Matt Dillon) writes: > > 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. > Both the 2090 and the 2090a board support 16 head st506 drives in hardware, however the early version of rom code only supported 8 heads. This is the rom that holds the z80 code. Months ago I modified the source and created a version of the z80 rom that would support my maxtor-1140 15 head drive and it seemed to work ok. I was told later on that then new rom would make it into the production line and should be on the 2090a boards when they are available. -- Dale Luck Boing, Inc. {cbmvax|oliveb|pyramid}|!amiga!boing!dale Although I do contract work for Amiga-LosGatos, my opinions probably don't represent those of Commodore or its management or its engineers, but I think the world would be a better place if they did.