General Category > LisaList2
dc42 images and known good checksums
sigma7:
--- Quote from: blusnowkitty on April 17, 2025, 03:38:46 pm ---When did XENIX 2.3 show up?
--- End quote ---
The dates on the files are 2011, is it actually 2.3 as the folder is named? Dunno. I thought these were on BitSavers, but I don't see them in the Twiggy folder.
stepleton:
Twiggy Xenix is new to me too. Google turns up no hits for "Xenix5of5.dc42".
TorZidan:
--- Quote from: sigma7 on April 17, 2025, 02:44:49 pm ---... Hence the suggestion to MD5 only the data portion of the DC42, eg ...
--- End quote ---
This is getting hairy because twiggy and sony400 and sony800 images have different data size. Also, an image like https://github.com/stepleton/LisaMandelbrot/blob/master/Solo/LisaMandelbrot_twiggy.dc42 is just 1KB, and is still a valid dc42 image (with just two sectors).
Instead of this md5 madness, why not use the 4-byte data checksum that is already calculated and stored in the dc42 header?
It is always at offset 72:
Example how to get it in Linux:
--- Code: ---dd if=BLU090.dc42 bs=1 skip=72 count=4 status=none | xxd -p
1858813c
--- End code ---
sigma7:
--- Quote from: TorZidan on April 17, 2025, 08:53:40 pm ---This is getting hairy ...
--- End quote ---
Agreed, but:
The checksum is not always valid; some dc42 files have a zero checksum indicating it was not calculated...
- Floppy EMU does (or did) this because recalculating on the fly is not practical (maybe images edited by Floppy EMU won't ever be a consideration, but I think it isn't impossible for someone to create a valuable image via FEMU).
- I have a couple of older images that predate BLU and Floppy EMU that have zero checksums; I don't know what software created them.
Others have an incorrect checksum because eg. someone has edited the data... possibly the best reason to MD5 is to confirm the data integrity vs identify the image
The variable file length is a complication -- the data length could be extracted from the dc42 header, eg. in the same way you extracted the checksum, and this should work for the sparse images too.
ried:
--- Quote from: blusnowkitty on April 17, 2025, 10:08:49 am ---Good find, I'm interested to see it in action - it looks like my first thought was correct, this is a Tektronics 4010/4050 graphics terminal emulator program that appears to have gotten ported over to the Mac later in life: https://books.google.com/books?id=zC4EAAAAMBAJ&pg=PA46&dq=%22tekalike%22+mesa+graphics&hl=en&sa=X&ved=2ahUKEwib8fPSnt-MAxXkRTABHZemF_wQ6AF6BAgIEAM#v=onepage&q=%22tekalike%22%20mesa%20graphics&f=false
I also found some snippets on Google Books implying that Tekalike did actually ship for Lisa... the dealer pamphlet also says Mesa Graphics was writing software for Lisa in 1983, think this is what they were writing? http://www.bitsavers.org/pdf/apple/lisa/marketing/Lisa_Dealer_Presentation_1983.pdf
--- End quote ---
Just added DC42 (BLU 0.9) Twiggy disk images for all three disks to the files section: https://lisalist2.com/index.php/topic,629.0.html
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