Chapter 4 Preliminary discussion of the logical design of an electronic computing instrument 119

mechanisms for preparing and printing from magnetic wires. Such converters are really nothing other than special purpose digital computers. They would seem to be justified only for those computers which are primarily intended for solving problems in which the computation time is small compared to the input-output time, to which class our computer does not belong.

6.8.3. It is possible to use various types of cathode ray tubes, and in particular Selectrons for the viewing tubes, in which case programming the viewing operation is quite simple. The viewing Selectrons can be switched by the same function tables that switch the memory Selectrons. By means of the substitution operation Ap ® S(x) and Ap' ® S(x). six-digit numbers specifying the abscissa and ordinate of the point (six binary digits represent a precision of one part in 2⁶ = 64, i.e. of about 1.5 per cent which seems reasonable in such a component) can be substituted in this order, which will specify that a particular one of the viewing Selectrons is to be activated.

6.8.4. As was mentioned above, the mechanisms used for preparing and printing from wire for the first model, at least, will be modified Teletype equipment. We are quite fortunate in having secured the full cooperation of the Ordnance Development Division of the National Bureau of Standards in making these modifications and in designing and building some associated equipment.

By means of this modified Teletype equipment an operator first prepares a checked paper tape and then directs the equipment to transfer the information from the paper tape to the magnetic wire. Similarly a magnetic wire can transfer its contents to a paper tape which can be used to operate a teletypewriter. (Studies are being undertaken to design equipment that will eliminate the necessity for using paper tapes.)

As was shown in 6.6.5, the statement of a new problem on a wire involves data unique to that problem interspersed with data found on previously prepared paper tapes or magnetic wires. The equipment discussed in the previous paragraph makes it possible for the operator to combine conveniently these data on to a single magnetic wire ready for insertion into the computer.

It is frequently very convenient to introduce data into a computation without producing a new wire. Hence it is planned to build one simple typewriter as an integral part of the computer. By means of this typewriter the operator can stop the computation, type in a memory location (which will go to the FR), type in a number (which will go to Ac and then be placed in the first mentioned location), and start the computation again.

6.8.5. There is one further order that the control needs to execute. There should be some means by which the computer can signal to the operator when a computation has been concluded, or when the computation has reached a previously determined point. Hence an order is needed which will tell the computer to stop and to flash a light or ring a bell.

BurkA62a, BurkA62b; CrawP??; GoldH63a, b, c, d; RajcJ43.