[Coco] micro drive configuration

jdaggett at gate.net jdaggett at gate.net
Wed Oct 14 00:01:15 EDT 2009


While it is late here and I may very well be wrong but it seems to me that it wont work 
very easily. To me it would seem that you run a risk of having either OS9 or DECB 
trashing the other half of the 512 byte sector during writes to the drive. Both systems 
would have to read the entire sector, modify the half that would be assigned and then 
write the whole sector back. 

I don't beleve there is a way to write either the upper of lower half of a disk sector. 
Though I could be wrong. 


On 13 Oct 2009 at 22:28, Roger Taylor wrote:

> I have an idea here that I need some feedback on in case I'm missing 
> something that might sneak up on me too late.
> Take a 2 gig "memory card" of any kind that the CoCo is interfaced to 
> and can access raw sectors for the memory and treat it as a "drive" 
> for OS-9 or Disk BASIC.  Currently, there may be systems in use that 
> use partitions to mark off an OS-9 area and a Disk BASIC area, or 
> possibly other areas.  I'm guessing that they 256-byte sector 
> controllers so that 1/2 of the memory card isn't lost.  If the 
> sectors are 512 bytes, then the OS probably uses both halves of the 
> sector which requires extra overhead... which I'm about to talk about.
> What if the memory card and host controller only dealt with 512-byte 
> sectors.  Would it be absolutely silly to let OS-9/NitrOS-9 have the 
> first half of the sector from LSN to LSN(end) and Disk BASIC have the 
> 2nd half of the sector from LSN0 to LSN(end) ?  I realize that a 
> read/write is involved for every write to retain the other OS'es 
> sector, and that a certain amount of speed would be lost for the 
> overhead.  The benefit would be that a 128mb, 256mb, 1gig, or 2gig 
> (just examples) memory card can be dropped in without having to tell 
> the CoCo "OS" anything about partitions or areas to stay out of.  The 
> idea is to use the drive in a parallel fashion and in the simplest 
> fashion, with no BASIC config program having to be used to configure 
> the "drives".  A 2 GIG card would yield 1 GIG for OS-9/NitrOS-9 and 1 
> GIG for Disk BASIC virtual drives, but then only 256 drives are ideal 
> so this is what I'm trying to work around without wasting any "hard 
> drive" space.
> Of course OS-9 and DIsk BASIC both would have to use only 256 byte sectors.
> -- 
> ~ Roger Taylor
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