FTYP of sub-directories on SDC...

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tofro
QL Wafer Drive
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Location: SW Germany

Re: FTYP of sub-directories on SDC...

Postby tofro » Mon Oct 30, 2017 9:14 am

Jan,

I remember something similar - And I also remember asking myself when I read that back then how a copy of something would help robustness when there are no means to verify the integrity of neither the original nor the copy (file headers have no checksum or anything to do that), even more so when the copy isn't a true copy.

In my opinion, there is lot of reasoning behind this scheme based on the need to speed up access time for microdrives (if you are working with a file there is a very high probability you have the sector containing the header in a slave block already, which reduces the read-modify-write time needed to update the header to one single tape revolution instead of at least two for updating the directory file which you probably have to read in first. That's 7 seconds... - And matters get even worse once the directory is spread over more than one sector, i.e. more than 8 files in the directory).

Quite a lot of this reasoning is pretty much void for more modern media like floppies or disks/silicon cards. They would be much better off by storing the header information in the directory file only (like most modern PC file systems do).

Tobias


martyn_hill
Gold Card
Posts: 403
Joined: Sat Oct 25, 2014 9:53 am

Re: FTYP of sub-directories on SDC...

Postby martyn_hill » Mon Oct 30, 2017 8:52 pm

Hi everyone

Just to close the loop on the original topic (which, as ever, has become soooo much more interesting then my original question!) I have been in touch with Wolfgang who, within 12 hours, provided a new release of QXLWinReader!

I've tested it and now FTYP returns the expected file-type of '255' for sub-directories copied across from a WIN drive to BDI image on my SD-Card.

I'll leave it to Wolfgang to tell us when he's ready to publish the new version on his site.

Do feel free to continue discussing the topic of dual file-headers!

M.



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