The Commodore systems famously wrote everything to the Datasette twice as a form of error correction. Most other formats I've looked at - Atari, CUTS and CoCo - lack any form of correction.
Is anyone aware of a format that used ECC on cassette storage? I assume this was not uncommon in non-cassette formats of the era.
Use of error-correcting codes was not common in home computers until at least 33.6Kbps modems and/or gigabyte-sized hard disks were available. One of the earliest consumer applications of ECC (in the form of two-dimensional Reed-Solomon codes) was the Compact Disc.
Until then, error-detecting codes such as parity and CRC were reasonably common, including in TCP/IP packets and floppy disk formats. If an error was detected, the computer might try a second time to read the data. Often this worked, and the extra time taken would alert the user that renewing the media might be a good idea.
Due to the nature of typical errors, simpler ECCs, like Hamming, would be of no use, and more complex ECCs would be prohibitively expensive.
For example, a burst of noise will corrupt several bits in a row, and if we're unlucky, and depending on the encoding mechanism, the synchronization may be lost, thus rendering all bits up to the end of a block or the file incorrect.
Not sure if VHS counts as a cassette storage, but ArVid did use ECC (Hamming in older models, Reed-Solomon in later models).
The Oric Atmos (not the Oric 1) had some kind of error detection (that was broken in the first version of the Atmos ROM) which printed "errors found" (without any further details) when loading encountered an issue. It wasn't based on a checksum, but rather on detecting a proper read of each byte of the tape (if it was using parity, it's at the hardware level).
When you saw that message (on a machine with the corrected ROM), it was generally too late (or the tape volume/speed required adjustment)
The Oric Atmos ROM also introducted an option to check the saved tape. Basically the user:
CSAVE "MYPROG")CLOAD "",V)That option loads and compares against the machine memory (not storing the data twice, but saving+checking doubles the time needed to save the data). If everything could be loaded once, at least it means that the save was successful (repeat process with another tape/another volume settings until it succeeds). And unless the tape rots, there's a good chance that the tape can be loaded again in the next future.
Those were heroic times, on amateurish computers, where it was admitted that you could lose your data from time to time (I lost a lot of work, just because sometimes I was too lazy to check my saves)
At least the Oric Atmos proposed a way to make sure that the save worked, without needing a second computer to load the saved data…
(Well, better save it on another tape from time to time, just to be sure)
