Conference hydra::amiga_v1

    Try ...dir/title=madness...
    
    besides marble madness you see hard drive madness...lots of stuff
    there, but I don't recall it answering this question! I re-read
    them recently too!

    According to my Adaptec Manual the ACB-4000 and ACB-4010 was a two
    module set that the ACB-4000A replaced.  This is a SCSI controller
    for ST506/ST412 drives.
    
    Alan
    

    ST506 drives can use SCSI controllers????

    re:.2
    
    thanks, the vendor is claiming that the 4010 is an OEM version of
    the 4000A.
    
    re:.3
    it's an adapter.  
    As in "host controller"----"scsi-to-st506 adapter"----st506 drive
    
    -dave

Re: .4

>    re:.3
>    it's an adapter.  
>    As in "host controller"----"scsi-to-st506 adapter"----st506 drive
    
This is backwards.

Actually, it's a controller.  ST-506 drives do not have come with a controller;
instead a controller leaves inside the computer and can control one or
two devices.

In the SCSI world, disks come with embedded controllers.  The controller
on the disk then speaks a high level protocol to a "host adapter"
which lives inside the computer.  All of those "SCSI controllers" people
talk about getting for their Amiga are really SCSI Host adapters.  A
SCSI host adapter is easier and cheaper to build than a real controller.
That one of the reasons why Apple can afford to bundle them with the 
Mac.  It's also why most third party Amiga disk "controllers" are SCSI.

The "adapters" being discussed are ST-506 controllers that instead of
delivering the data straight to the computer's buss instead talk SCSI
to a host adapter living in the computer.  So the adapters are really
controllers and the controllers are really adapters.  Get that?

    
Re: .5

>>    re:.3
>>    it's an adapter.  
>>    As in "host controller"----"scsi-to-st506 adapter"----st506 drive
    
>This is backwards.

    No, it is not.  It depends on your use of the jargon.  I've tried
    explaining to pc users about the wonders of SCSI, but it all comes
    down to what the expectations are.  The board you plug into a pc
    slot is a controller, since it is what you need to talk to a harddisk.
    You run a cable from it to the harddisk.  For an harddisk with builtin
    SCSI, that is all you need.  So it appears that all you have is
    "controller ----- harddisk (scsi)"
    
    If the harddisk speaks ST506 instead of SCSI, you need to get an
    adapter.  The fact that the adapter does the actual controlling
    of the drive is a detail buried at a deeper level than "what do
    I need to hook up a harddisk?".  It shows up when they ask "why
    would I want SCSI, instead of ST506?"
    
    Consider, which is the controller?
    1. the board that issues the commands to do something
    2. or the board that actually does the commands
    
>In the SCSI world, disks come with embedded controllers.  The controller
>on the disk then speaks a high level protocol to a "host adapter"
>which lives inside the computer.  All of those "SCSI controllers" people
>talk about getting for their Amiga are really SCSI Host adapters.  A
>SCSI host adapter is easier and cheaper to build than a real controller.
>That one of the reasons why Apple can afford to bundle them with the 
>Mac.  It's also why most third party Amiga disk "controllers" are SCSI.

    Ahh.. I thought it was because they wimped out on providing slots
    in the Macintosh and other computers.  The ibmpc market seems to be doing
    ok without SCSI.  I'm not so sure about it being cheaper to build,
    isn't the chip count on a real controller down to one chip?  The
    reason for SCSI is the features it offers over ST506, not the cost.
    Like faster speed, intelligent devices, one controller board
    controlling more than two devices, etc....
    
    -dave

Re: .6

The point of .5 was it was just a question of semantics.  The people that
defined SCSI defined it claiming that the thing in the computer is the
"host adapter" and the intelligence on the disk was the controller. 
Although those are the technically correct terms, they seem to be more
or less universally ignored.

>I'm not so sure about it being cheaper to build, isn't the chip count
>on a real controller down to one chip?

I could be wrong about SCSI being cheaper.  I've heard the claim before,
but I don't remember my source.

	The scoop on Adaptec 40xx:

	4000 ($85-125) - scsi to st506 MFM controller
	4000a ($125) - NEW scsi to st506 MFM controller
	4070 ($125-190) - scsi to st506 RLL controller
			As mention in note 870.2, a RLL controller will
			get you a extra ~50% capacity (i.e. 20meg drive at
			MFM = 32.8meg using RLL).  But, C-ltd warns that hard
			disk certified only for MFM (i.e. ST225) should not
			be used with a RLL controller.  I guess it's like
			using single sided floppies as double sided (i've had
			good luck with Sony SS-DD, only one bad in 40 disks).
	4010 ($60) - removable hard disk, scsi to st506 MFM controller
			C-ltd has told me that they've had some minor problems
			with this unit (ie. random "disk error" which are
			really "removeable disk drive door is open error").
			C-ltd said that some of the scsi command map into
			"removeable disk drive" commands in this adapter.
			I bought one, so I'm taking my chances on this one.

_Mike