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Replacing the internal ROM with a 512KB flash chip allows for the Z88 to be upgraded to a more modern OZ version without consuming a flash card in Slot 1. Most machines with this modification run OZ 4.7.1.
However some useful Z88 software does not function on the these newer OZ versions, since authors were known to deviate from the Cambridge developer guidelines. Vision2 VT100 terminal is one such application. Using a Z88 as a portable serial terminal, with its full size keyboard and long battery life, remains a useful proposition even today.
Historically, once a Z88 had a Slot 0 flash modification and an OZ upgrade was performed, it could no longer run legacy applications… until nowthis flash ROM downgrade package!
Legacy OZ Version Selection
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After using OZ 4.7.1 or OZ 5.0 it's easy to forget just how irritating it can be returning to one of the stock versions. Simply transferring files is a chore, often painfully slow since EazyLink2 standalone is limited to 9600bps. However, Dennis Gröning's XY-Modem can achieve around a 10x speed improvement, explained in this guide.
Since my own updates in 2022, all of the essential flash tools above have been updated to add compatibility for newer flash memory types - so they remain current even running on old OZ versions.
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