[Coco] RE: Tandy Hard Disk Controller

[Boisy Pitre]

I can state pretty much unequivocally that there is no possible way  
to detect the type of collision problems that can occur by two CoCos  
sharing a single SCSI drive, short of having some type of  
communication between the CoCos themselves.

This would require that the CoCo wishing to write to the drive pass a  
message to the other CoCo with a start sector and sector count before  
it writes to a particular section of the drive.  The CoCo receiving  
the message would have to put off reading or writing to that area  
until the initiating CoCo indicates that its write has completed.   
Such a scheme would slow down I/O a bit, as every write would need to  
be prepended and appended with this information.

A more meaningful method of using a single SCSI hard drive connected  
to two CoCos (which would not require the above communication  
scenario) would be if CoCo #1 used a separate area, or partition of  
the disk than CoCo #2.  That way reads and writes would stay out of  
the way of each other.  Or in the case of a SCSI drive that does not  
need to be written to, two CoCos could easily share the same data.

There was a review of the Ken-Ton hard drive system back in 1989 or  
so, which appeared in the now defunct CoCo Clipboard Magazine that  
detailed this scenario.  It was written by none other than Jim  
Distefano (anyone remember him? :)

Boisy

On Mar 6, 2006, at 7:51 AM, Mike Pepe wrote:

> L. Curtis Boyle wrote:
>>    I do know that Ken (of Kenton) had demoed an RS-DOS system at  
>> Rainbowfest that did have 2 Coco 2's hooked up to one SCSI hard  
>> drive... but I don't remember any of the details. I would presume  
>> it would "just" be a driver issue.
>
> It's not a big deal. The drivers are very simple and shouldn't  
> care. Really there are only a few things to worry about:
>
> 1- you need to be able to set each CoCo host adapter to use a  
> different SCSI ID.
>
> 2- you need to maintain proper bus termination.
>
> and
>
> 3- you best not write to the same file(s) at the same time.  
> Multiple reads should be just fine.
>
> Note that you can (technically) also wire up and share floppies in  
> a similar manner.
>
>
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