Mini Utility Disc: BBC Micro bootstrapping

Virtually all BBC Micros that have disc interfaces come with matching firmware in ROM; but the standard Acorn DFS doesn't have a built-in command to format discs. If you don't have the original utility disc, you can bootstrap by creating a one-track volume containing the Acorn formatter and verifier.

After that you can format more discs and write disc images to them using other utilities such as Xfer in C and DFS Explorer.

Later DFS versions based on double density floppy drive controllers had a formatter built into the ROM.

The program to create the mini utility disc can be read in through the serial port or loaded through the cassette port. The one-track disc can be reformatted to full capacity without losing the utilities.

The 'dropper' is 3.5 KB long, self-contained and features a uudecoder in ~100 bytes of code that unpacks the rest of the program.

This video also shows that KCS/CUTS/BYTE format audio signals survive MP3 encoding, as long as a high enough bitrate and a good enough encoder are used.

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• retrocomputing
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• serial
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