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FreeDOS on SBC188 (Announce)

posted by ecm Homepage E-mail, Düsseldorf, Germany, 14.09.2020, 13:35

> > > > By the way, how much memory is installed on this system and
> available
> > to
> > > > DOS?
> > >
> > > 1Mb
> >
> > It is unlikely that the entire MiB is available to DOS, which expects at
> > most 640 KiB generally. (It can be higher, but not a full MiB.) Try
> running
> > ldebug /C="a;int 12;;t;h ax * #1024;q" (You can use the
> > executable in the second archive I posted.)
>
> [image]
As expected there's 640 KiB of low memory available to DOS. It is highly likely that this is the same as available to the dot-displaying boot sector loader, which means that a lack of memory is not a cause for its failure.

By the way, it might be possible to have a special driver offer some additional memory (between 640 KiB and 1024 KiB) to DOS as upper memory. If so then your DOS=UMB setting could take effect and DOS could link such memory as UMBs into its memory chain.

Perhaps such a driver already exists for the SBC188. I created such a driver for the 8086tiny environment. However, it would have to be adjusted to work with the SBC188. And it would be crucial to know exactly which memory areas are both backed by actual RAM and available for us to use. As I stated in the readme: "the UMB area is assumed by the DOS driver. (This is 128 KiB (2000h paragraphs) between segments D000h and EFFFh.)"

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l

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