Re: SCSI Apple II

[nparker@cie-2.uoregon.edu (Neil Parker)]

In article <3354236c.6076953@167.152.149.11>
LOSETHECAPITALWORDSedhel@bigfoot.com (Edhel Iaur, Esq.) writes:
>On 11 Apr 1997 00:23:59 GMT, nathan@visi.com (Nathan Mates) wrote:
>
>>   What's far better is to just move any SCSI devices to the chain of
>>the other computer and connect there. Having multiple computers on the
>>same SCSI chain is a bad idea unless both the hardware and the
>>software on both ends is written to provide safe access to the
>>'shared' drives. [Tip: I wouldn't want both machines trying to write
>>to the same drive at once unless they did it right.]
>
>What if only one of the computers was on at once?

That should work just fine.

The problem arises when two computers are plugged into the same drive, and
both are turned on at the same time.  If both machines try to write the
same disk at the same time, they're practically guaranteed to corrupt each
other's data unless their operating systems have been specifically designed
to prevent such disasters.

Actually, the disk accesses don't even have to be simultaneous for the
problem to arise.  If either computer caches any disk data in its memory,
even for an instant, and the other computer accesses the disk while the
data is cached, you'll probably end up with corrupted data.

I'm unaware of any operating system for the Mac or the PC (or even the
Apple II) that implements the protections necessary to reliably share a
disk in that manner.  In the absence of such protections, the only safe way
to do it is for each computer to have its own private partition on the
shared disk, and never access anything in the other computer's private
partition, or try to alter the partition table.

               - Neil Parker
-- 
Neil Parker, nparker@{cie-2,cie}.uoregon.edu, http://cie-2.uoregon.edu/~nparker
                     "Bad move, Neil!"  -- The Tick

Unsolicited commercial e-mail to my address will be discarded unread.