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Old 25 June 2012, 01:44   #61
prowler
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Join Date: Aug 2008
Location: Sidcup, England
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Well, finally, here is some better news.

A brief summary of what I have achieved over the last few days:

Despite still having captured nothing but corrupted rubbish from Disk Block 116, I think I'm on the brink of recovering the Calc program.

The closely matching data I found for Disk Block 116 in the Advantage Disk 2[a] image in TOSEC turned out to be from the English version of the Calc program.

Initially, I estimated the degree of closeness of these blocks of data by noting that the next block of data on each disk differs by only four bytes.

And so it has proved to be. After many, many captures from the Office Disk's Block 116 I have established the likelihood that the bulk of the replacement data I am using is correct and that there are just four bytes (the same number of discrepancies as in the next block) which do not match.

I appreciate that it would still take a huge amount of effort to establish the correct data for these four bytes using a brute force method, but I can now conduct a fresh analysis of the captures I have made so far to predict them on a maximum likelihood basis, plus I may yet find a disk drive which can read that block more effectively.

The Graph program on the Office disk also has a data block which closely matches Disk Block 116 (though not quite as closely as the English Calc program's), and there is also an English version of the Graph program in the Advantage Disk 2[a] image in TOSEC. This program has a five bytes discrepancy between the Portuguese and English versions both in the relevant data block and the next one, and both files are intact!

I intend to do some comparisons between the Portuguese and English versions of both the Calc and Graph programs, to see if I can discover the reason for the discrepancies, which would probably enable me to establish the correct data for the four bytes in Disk Block 116 without any guesswork.

Last edited by prowler; 25 June 2012 at 01:50.
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