Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!oliveb!apple!mattd
From: mattd@Apple.COM (Matt Deatherage)
Newsgroups: comp.sys.apple
Subject: Re: SCSI slot problems on the apple II
Message-ID: <30471@apple.Apple.COM>
Date: 11 May 89 04:38:36 GMT
References: <8905100737.AA12945@crash.cts.com>
Organization: Apple Computer Inc, Cupertino, CA
Lines: 52

In article <8905100737.AA12945@crash.cts.com> pnet01!pro-sol!pro-nucleus!hzink@nosc.mil writes:
>Here's my problem, and hopefully someone will have a solution (of some kind).
>
>As you know, if you run a SCSI drive on the apple II series, Prodos can
>address two devices per slot.  This applies to all slots, except slot 5,
>whehre you can have 4 SCSI devices (2 of them shadowed in slot 2).  So far so
>good.  Now let's examine the intelligence behind implementing this scheme.  
>
>Obviously, slot 6 is always reserved for floppy drives, slot 5 is a normal
> [attempted justification for this deleted]

>Anyway, enough gripes from me here, my question pertains to a possible
>solution.  I assume that there is special code in Prodos that decides that
>slot 5 has the special abilities, and all other slots are normal.  I also
>assume that the selection of slot 5 was more or less arbitrary (If I'm wrong
>on any of these assumptions, feel free to jump in any time).  Now, is there
>some way to patch/modify Prodos to give slot 7 the abilities it should have
>had in the first place, i.e. the ability to address up to 4 SCSI devices?  
>
>Has anyone experimented with some modifications that would allow this, or
>successfully implemmented them?  If so, please share this information with the
>rest of us (most of all ME), so we can run our hard drives from slot 7 once
>again.
>
>profound thanks to those answering this.
>
>        hzink@pro-nucleus
>        crash!pnet01!pro-nucleus!hzink : UUCP
>                                                +
The justification for this is pure, and simple, and even close to logical.

At boot time, ProDOS 8 looks at slot 5 and looks for a SmartPort firmware
interface there.  If it finds it and it has more than two devices connected
to it, the third and fourth devices are shadowed to slot 2.  This was done
so that more than two devices (3.5" drives and RAM disks) could be used
with the IIgs SmartPort in port 5.  It just so happens that the Rev. C
SCSI card was later designed such that it could also handle being shadowed
to slot 2 if placed in slot 5.

It is no massive "hard disk usage" strategy; it's simply a side effect of
how ProDOS 8 was modified to work on the IIgs (without this, any RAM disk
would mean a second 3.5" drive would be unusable).

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