On 27 Oct, 2006, at 07:41, ard at p850ug1.demon.co.uk (Tony Duell) wrote: Not all classic computers are micros. Fancy tracing the schematic for my 500 square foot second generation mainframe? Fortunately I have most of them, along with the 'address book' which lists every logic signal, its sources (think wire-OR) and destinations. Its on roughly A3 paper and is in two volumes four inches thick. Welcome to the new chap. BCD is not just a bit coding, its a card code as well. It lacks things like parentheses and brackets but has things like 1/4, 1/2 and 3/4. My 1301 uses it, though strangely there is not a one to one mapping printer! The old Friden Flexowriters used a similar code too, though they seem to have varied too. The old Elliott 920 code was different read 8 paper tape, or using the same mechanism, along the edge of a punched card size medium which I think could be fan-folded. I guess this allowed the operator to write on the rest of the card). Roger Holmes (Who has at home what might be a collection of the largest computers in private ownership - unless you know different as Esther Rantzen used to say on "That's Life").