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EDR-DOS repository - Single-file kernel load (Announce)

posted by ecm Homepage E-mail, Düsseldorf, Germany, 13.10.2023, 18:16

> > I don't think it is required to combine the file. It is good for other
> reasons though.
>
> What are the other reasons?
Several:

* BIO and DOS file can get out of sync, potentially resulting in failures to boot or even data corruption.
* One more file to keep track of.
* Need a FAT FS read implementation in the BIO that is only ever used to read the DOS file, this is in bdosldr.a86 for EDR-DOS, called by the BIO init routines here.
* The BIO kernel has to locate the DOS file, meaning it will have to include a directory scanner. (Arguably, lDOS iniload contains just as much of a FAT FS reader (to read the remainder of the kernel file) as EDR-DOS's BIO file, but lDOS iniload certainly does not need a directory scanner.)
* Compression of kernel files also needs two bespoke solutions, one for each file, whereas lDOS iniload + inicomp has a single compression stage which depacks the entire remaining kernel. This can make for better compression ratio than compressing two files, too.

Back in the day I discussed this with Udo in the EDR-DOS forums. However, that thread is likely lost to time. I recall that Udo brought up you can update one of the files without the other, and vendors could get away with only providing a BIO file sharing a common DOS file that they wouldn't have to know much about. At the time I already noted that this last advantage is minor if the entire kernel is available as free software.

The second link that I included in my list also hints it is possible for the DOS to be resident somewhere already, and not have the BIO load it from a file. This means part of the work towards a single-file kernel may already be done.

---
l

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