Originally, I thought that the problem with dir exiting with an error, and the jumble appearing on screen as my "DRIVEDFILE" filename, were one and the same, but it turned out that there was no problem with the filename - the way it is displayed in DOS Plus is deliberate!

This is because DOS Plus follows the convention of 8-character filenames, plus a 3-character suffix, usually used to identify a file by type. This system is sometimes known as DOS "8.3" which is nothing to do with the version number.

So, what does DOS Plus with Econet do with the 2 characters which won't fit in the 8 characters allowed in DOS Plus? You might think the sensible thing would be to put them in the 3 character extension, but no, instead, it encodes the final two bytes of a filename into two 4-bit nybbles, and distributes those 8 bits across the 8 characters of the DOS name.

As shown here, when I was working it all out. We take the last two characters, deduct the ASCII code for "a", and that gives us a 4-bit number. Results outside that range are disallowed by this conversion process. Reversing the two nybbles of those two characters gives us an 8-bit number, and for each bit set, the byte in the 8-character DOS name is replaced with a byte from a lookup table.

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