Re: IIgs doesn't see the SCSI harddrive.........

[dempson@actrix.gen.nz (David Empson)]

william strutts <wrstrutts1@nospam.home.com> wrote:

> "Marsha" <menacechgo@aol.com> wrote:
> > Courtney Thomas <ccthomas@flash.net> wrote:
> > > Under 6.01, an external 2.15Gig Seagate Barracuda attached to an Apple
> > > SCSI card is not detected. The card is in slot 7 and the ID is 7.
> >
> > When you mention SCSI ID 7, are you talking about the card or the drive?
> > Make sure the drive doesn't have the same SCSI number... For convenience
> > my system has it's drive set to ID 4 so I could occasionally plug in
> > other drives and boot order.
> 
> What does that matter? The Apple Card takes up SCSI ID 0.

No it doesn't.  It takes up a single SCSI ID, which by default is 7.
You use jumpers to set this with the original Apple SCSI card (one of
the eight pairs must be jumpered), or three of the four DIP switches on
the high-speed SCSI card.

The computer should be the highest priority device on the SCSI bus,
because that guarantees it will "win" any arbitration clash with a
peripheral.

> The boot device should be the highest numbered SCSI ID because
> that has priority over the other SCSI ID's.

Apart from the issue of host vs peripheral, the use of the SCSI ID to
set the relative priority of peripherals is not relevant on the Apple
II, because little if any software supports issuing simultaneous
requests to different SCSI peripherals, then detaching and waiting for
them to reply.

The only significance of the SCSI IDs on the Apple II are:

- They must be unique (including the host).

- The Apple SCSI card firmware uses the priority to determine which
device to boot from (scanning from ID 7 down to ID 0, skipping its own
ID).  The order in which the drives appear is also affected by this.

- You can force a delay at startup (e.g. to give time for your hard
drive to get ready after being powered on) by using a lower ID for your
boot device, as it takes the SCSI card longer to find it.

> I have mine on SCSI ID 6 because that is the highest my drive supports.

If it was designed to work on a Macintosh, that makes sense, because the
Mac's SCSI ID is fixed at 7.

> However, on the RamFAST, the card doesn't take a SCSI ID

This means that the RamFast cannot support overlapped SCSI operations
and does not implement the SCSI arbitration mechanism.  It also means
that some recent hard drives (notably the Quantum Fireball series) does
not work on a RamFast.

I think the RamFast can be configured to boot from an arbitrary device.
It defaults to scanning SCSI IDs in descending order.

> but on the Apple SCSI it does.  He just has to make sure the HD and the
> Apple card don't use the same ID.

No arguments there.