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BIOS-143 is JSON-encoded dump of the ROM images (OLIVETTI_M24_VERSION_1.43_LOW.BIN and OLIVETTI_M24_VERSION_1.43_HIGH.BIN) obtained from www.minuszerodegrees.net.
The dump was produced by running FileImage to merge the even and odd portions (8Kb each) to produce a single 16Kb ROM image:
fileimage --file=archive/OLIVETTI_M24_VERSION_1.43_LOW.BIN --merge=archive/OLIVETTI_M24_VERSION_1.43_HIGH.BIN --output=BIOS-143.json5 --comments --format=bytes
NOTE: The AT&T 6300 ROM BIOS is apparently identical to the Olivetti M24 ROM BIOS.