[Coco] Largest supported HDD size?

[Gene Heskett]

On Wednesday 30 November 2016 03:15:39 RETRO Innovations wrote:

> My google fu must be lacking tonight, as I thought it would be trivial
> to see how big a HDD is supported on the Coco via an IDE or SCSI
> interface, but I came up empty.
>
> I figured the CocoSDC can use an unlimited drive, as you mount images
> by name, but what about the GLenside IDE or the various SCSI systems? 
> Is it really 255 drive images * 170kB, or is there another limit?
>
> Jim
>
Jim, you can have as many "banks" of those 256 disk images as you've 
drive space, up to a little over 4 Gigabytes. One could keep a paper 
copy of the offsets, and either add another device descriptor, or dmode 
the values of ofs and the other byte, w something IIRC that determines 
the offset into the drive where that bank of 256 images start. 
Each "bank" occupies 41,287,680 bytes of disk space. (If I pushed the 
right buttons on the calculator) Start the next "bank" at the next 
sector after that allocation.  Step and repeat till out of disk or a 
hair over 4Gigabytes total for both rsbasic and for Nitros9, my main 
disk is just short of 500 megs for os9, and my first bank of floppies, 
which can be formatted for rsbasic or os9 on a disk by disk basis 
anyplace, the limit is reached when this 3 byte value overflows.

But I doubt any of us has enough floppy disks to fill up a 4Gb drive. :) 
What I have wouldn't fill up the 1Gb drives I use.

I don't mess with rs-basic all that much but in the coco3's memory, the 
offsets are kept in an address starting with $D9xx, and is a 3 byte long 
value.  Its been mentioned on this list so a search should find the full 
address triplet easily. From basic, poke those 3 bytes with the new 
offset values in order to change the "bank" of 256 disk images of 35 
tracks, single sided each.

> --
> RETRO Innovations, Contemporary Gear for Classic Systems
> www.go4retro.com
> store.go4retro.com


Cheers, Gene Heskett
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