General Report on Tunny

13B Page 26

approximate count. For details see 91.

(a) Colossus.

Colossus has a "bedstead" round which the Z tape is driven by pulleys so as to be scanned at 5000 letters per second; and "triggers" in which chi, Mu, Psi patterns may be set up.

The counts most commonly required are of ΔD = ΔZ + ΔΧ and P = Z + Χ + Ψ'. For these there is a switch panel which imposes conditions on Q, where Q is, at choice, any sum, with or without deltaing, of Z, Chi, Psi.

The Q panel suffices to select almost any arbitrary group of letters, but is kept reasonably small by 'not' switches: "either A or B or C" is replaced by the equivalent "Not (not A, not B, not C)".

There is a plugboard for conditions not expressible in terms of Q. It has no "not".

The effective speed is increased five fold by five separate counters which, in particular, can be used for counting at five different settings simultaneously (multiple test).

Specialised facilities include "not 99", for ignoring the 9's used to replace corruption; "spanning", for selecting a part of the text; "set total", for cancelling scores too small to be of interest.

On some Colossi there is an elaborate rectangling gadget; on others a wheel-breaking panel.

Scores are displayed and printed.

Colossus is the standard machine for wheel-setting and breaking: it is too large to replace hand work economically in all cases.

On Colossus only one pattern is arbitrary vis. the tape, the others being restricted by wheel periodicities. If two arbitrary patterns are to be compared Robinson is used.

(b) Robinson.

In pre-Colossus days the old Robinson did much of the work now assigned to Colossus, and, considering its primitive character, did so with remarkable success.

The present 'Super Rob.' has four bedsteads, a plugboard rather more flexible than that of Colossus, a very meagre switchboard, "span" and "set total". It lacks the immense elaboration of facilities provided by Colossus.

Its advantage is that patterns punched on a tape are completely arbitrary; its disadvantage that they are difficult to change.

Since Colossus became generally available, Robinson has been used mostly for cribs and for experimental work, occasionally for rectangling.

(c) Specialised Counting and Stepping Machines.

These are Dragon, for setting short cribs in de-chis; and two machines which arrived too late for operational use: Aquarius, for go-backs and Proteus for depths.

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