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From: lsr@Apple.COM (Larry Rosenstein)
Newsgroups: comp.sys.mac
Subject: Re: comp.sys.mac
Message-ID: <4839@internal.Apple.COM>
Date: 23 Oct 89 18:18:21 GMT
References: <10453@cbnews.ATT.COM>
Sender: usenet@Apple.COM
Organization: Objects-R-Us,  Apple Computer, Inc.
Lines: 40

In article <10453@cbnews.ATT.COM> saw@cbnews.ATT.COM (stephen.a.wilkus) 
writes:
> Unfortunately, I've had some problems with the SCSI port.  I have 
connected 
> two external hard disk drives to the /ci and the machine (intermitantly) 
> either failed to boot (sad MAC with 0000000F/0000001 displayed) or else 
it 
> booted up without recognizing the hard disk. I tried various cables, 
> terminators, and SCSI addresses all to no avail.  Both drives work on Mac
> Pluses, Mac-II's, and MAC-II/cx's. 

Tech Note 258 and Inside Mac volume 5 might explain your problem.

It turns out that the ROM boot code is supposed to validate the disk 
driver by computing a checksum.  Due to a ROM bug, the checksum 
verification was never done UNTIL the Mac IIci.

The problem is that there are a number of 3rd party SCSI drivers that 
don't implement the checksum verification properly.  On the Mac IIci is 
the verification fails the driver won't be loaded and the disk won't be 
usable.

Another problem is that some SCSI drivers call SysEnvirons at boot time.  
Unfortunately, SysEnvirons is documented to require that all Toolbox 
Manager be initialized before it is called, which is not true at boot 
time.  A disk driver that calls SysEnvirons is likely to crash.  (I 
suspect that this worked on earlier machines because SysEnvirons was 
installed by a RAM patch, which means it wasn't available at boot time.  
On the Mac IIci, SysEnvirons is in ROM.)

The solution is both cases is to get an updated SCSI driver from the maker 
of your hard disk.  Generally, this is a simple software fix.  If you've 
gotten otehr SCSI devices to work, then it sounds like the SCSI hardware 
is OK.  

Larry Rosenstein, Apple Computer, Inc.
Object Specialist

Internet: lsr@Apple.com   UUCP: {nsc, sun}!apple!lsr
AppleLink: Rosenstein1