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Re-watching an episode of The Computer Programme, I notice a couple of unusual characteristics of the BBC Micro text – more specifically, program listing as software-generated text on bitmap – display, which can be seen e.g. at 21:16.

  1. The text is white on blue, but the text rows are separated by a couple of scan lines of black. The BBC Micro has vertical resolution 256, which is enough for 32 rows of text; this is clearly using one of the modes that only use 25 rows, leaving extra scan lines between the rows.

  2. The LIST command shows the program with a blank line between each line of code. That's not something you would normally want; it would effectively restrict you to listing 12 lines of code on the screen. Presumably it is a mode provided by the Basic interpreter.

The first is documented as a characteristic of the hardware, but I don't remember seeing any rationale for it. I don't remember the second being mentioned anywhere.

Did the BBC ask for both of these kinds of extra line spacing modes, in the belief that it would make it easier for viewers to read the short program listings?

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  • 4
    The BBC Wiki (beebwiki.mdfs.net/MODE_3) seems to indicate that it was to provide a monochrome 80x25 display that would be compatible with online bulletin boards, and it also used less memory. The coloured rows ability was probably a happy side effect that made listings easier to read.
    – Alan B
    Commented Jul 30 at 13:42
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    Re: (2), having grown up with an Acorn Electron that is definitely not default behaviour, and I was previously unaware of the option. It looks like the entire display is double-spaced, not just LIST, so I guess it's a VDU<something>.
    – Tommy
    Commented Jul 30 at 14:47
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    Another important factor is the reduced memory consumption: MODE 3 took 16KB, saving 4KB over the other 80-char MODE 0; similarly, MODE 6 took 8KB, 2KB less than MODE 4.  When you have only 32KB, of which 3½–6¼ is used by the OS, every little helps!
    – gidds
    Commented Jul 30 at 21:21
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    There's a discussion of this very thing on stardot: Double carriage return? - stardot.org.uk, but they're not able to exactly replicate or come up with a rationale
    – scruss
    Commented Jul 30 at 22:24
  • Remember the BBC micro was often used with low quality "monitors".
    – Ian Ringrose
    Commented Jul 31 at 8:43

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The monochrome 80x25 display of Mode 3 was intended for word-processing, as well as bulletin boards. I did a lot of word-processing in the 1980s with Acornsoft View, and the 80x25 mode was definitely easier to read than an 80x32 mode.

The BBC Micro's built-in fonts are designed on an 8x8 pixel grid. With no added linespacing, this is not easy to read for an extended period. As your eyes scan along the lines, it's easy to "slip" to the line above or below the one you're trying to read. With the inserted vertical space, that problem was much rarer and reading was easier.

Double-spaced BASIC program listings certainly weren't the default. I'll believe there's a call to produce them somewhere, but I can't find it in the BBC micro wiki.

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