[Coco] HDB-DOS Eprom

[Gene Heskett]

On Saturday 19 March 2016 18:11:04 Tormod Volden wrote:

> On Sat, Mar 19, 2016 at 12:40 AM, Gene Heskett wrote:
> > On Friday 18 March 2016 17:06:01 Mathieu Chouinard wrote:
> >> > That is sector offset to the beginning of the HDBDOS/basic disks,
> >> > and allows 94,371,840 megabytes for os9, which is about 3/4 of
> >> > what can be handled with a cluster size of 1.  Above about 132
> >> > megs it needs a cluster size of 2, then 4 at just above 250 megs,
> >> > moving up in powers of 2, so my 1Gb seagate I have as S1, is
> >> > running with a cluster size of 16, or $10 in hexidecimal.  We run
> >> > out of cluster size room at about 4Gb IIRC.
> >>
> >> is there some document that explain how to do it?
>
> Some is explained here, page 7-5, on "segment allocation size",
> http://www.icdia.co.uk/microware/tech/tech_7.pdf
>
> > I don't know as there is an official document, but it works like
> > this, at a cluster size of one, each bit in the allocation map
> > represents a single sector. The map itself is limited to 65536
> > bytes, 64k IOW, so the map can represent 8 x 65536=522,944, 256 byte
> > sectors, and that is 133,873,664 bytes of disk.  Above that to
> > double that to 267,747,328 bytes, it needs a cluster size of 2, then
> > double that again for 535,494,656 bytes it needs a cluster size of
> > 4. You just keep upping both figures by a power of two until you are
> > out of a 1 byte cluster size, and you are something above 4Gb, at
> > which point you are up against the 3 byte offset limit of a sector
> > seek anyway, so you never hit a full 256 sectors per bit in the map.
> >  Your minimum allocation is one cluster. At a cluster size of $10,
> > aka 16, one could use a sas of 2 or 4 and still have room for the
> > average coco sized file in one FD.SEG entry.  We have had our files
> > grow in average size over the years, so the default SAS=8 is
> > occasionally a problem, so I have been advocating a SAS of $10,
>
> I don't think the default segment allocation size is 8. It was changed
> before NitrOS-9 3.3.0 here:
> https://sourceforge.net/p/nitros9/code/ci/e881994bfe30017541c516107b24
>4b57ccb6355f/
>
> However it looks like you set it to 10 (decimal) in rbfdesc.asm, and
> to $10 in superdesc.asm
> Should it maybe be $10 both places?
>
> > or for known huge files, set it for $FF temporarily, so you never
> > run out of FD.SEG's, which can be an un-recoverable problem in some
> > cases.
> >
> > Once the file has been written and closed, os9 cleans up and returns
> > any of that unused SAS to the system, so you don't lose anything by
> > running a big SAS except the ability to stuff a disk to the last
> > byte.
>
> Yes, the SAS is only used to reserve space while the file is open, and
> the extra sectors are de-allocated when the file gets closed, /if/ the
> file pointer is at end-of-file. If the file pointer is in the middle
> of the file upon closing, the extra space is not de-allocated, if I
> read above OS-9 docs correctly.
>
> Tormod

I believe you are.


Cheers, Gene Heskett
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