MECHANICAL STORAGE .1 Punched Hole Storage

The idea of storing information by punching or not punching holes in specified locations on tough pa-per cards or tape has been in existence a long time. By arranging regular rows or columns on a card or along the length of a tape, binary numbers can be permanently stored by the punch (I)-no punch (0) system.

When a card or tape is properly aligned and drawn between a metal plate and a set of metal wipers or fingers, a brief electrical contact is made through each hole. None is made where there is no punch. Thus,

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Control Panel Storage 4.5.1-4.5.2 punch-no punch is translated to pulse-no pulse, which

is understood by the computer.

A newer and faster method of reading punched in-formation is to draw the card or tape between a light source and a set of photocells (one per row or column).

Each punched hole lets through a flash of light to the corresponding photocell, which produces an electrical pulse, so again the informamtion is translated to com-puter language.

Punched cards and tape are not well suited for use as either main or auxiliary storage mediums in modern computers, because of the necessity for frequent han-dling by an operator as well as because of the slowness of access. For this reason, punched card and tape ma-chines are most often used as input-output devices and, as such, are described in Chapter 4.

4.5.2 Control Panel Storage

A telephone switchboard might be considered to be a type of memory device. Each time the operator plugs in one of the patch wires, she sets up a connection that will "remember" which circuits are connected. In com-puter usage, a similar storage device is the control panel, often called a plugboard. A device of this type, some-times used to store programs and data by means of plug-wires, is shown in figure 3-91. Information is stored in it by connecting certain hubs (holes) together with pluggable wires.

Two general types of control panel storage are used. In some machines, the control panel is used purely for storage of control information (the program). In this case, the control panel usually consists of two types of hubs: exit hubs and entry hubs. In general, the exit

Figure 3-91. Control Panel

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hubs are hubs which emit pulses. Entry hubs are con-nected to circuits controlling various machine functions.

Therefore, when they are pulsed, the functions they control are initiated. During each machine cycle, the various exit hubs are pulsed in certain sequences by the machine. If one of these exit hubs is .wired to an entry hub controlling a particular function, the pulse, when it appears, initiates this function. For instance, a exit hub might be wired to the entry hub which initiates the addition function. Then, when the machine pulses this exit hub, it will cause the machine to add.

Another type of control panel storage is more like the register storage which has been mentioned before.

In this case, the control panel is divided into registers, and each bit position of each register consists of a pair of hubs. In such a system, a 1 is usually represented by a wire connecting the two hubs of a pair, a 0 by no connection between the two hubs. A 5-bit register, for example, has five pairs of hubs. If the first, third, and fifth pairs were connected together and the second and fourth left unconnected, the register would contain 10101.

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PART 3 and receiving information for digital computer opera-tion. This chapter will consider those devices which are actually used.

5.1.2 Definition of Input-Output Devices

The equipment that introduces input information into the computer and receives output information from the computer may be the same device. The function of this device may vary between its input and output util-ization. For example, a tape unit may be used as a mem-ory storage, as an input source, or as an output device.

However, the general characteristics and capabilities of the tape unit are fixed and do not vary with its func-tion.

An input or output device may be defined as equip-ment for communication between the computer and the external sources or destinations of information and data; devices may be classified as input-output equip-ment if they can translate external information into computer information or vice versa.

5.2 DESCRIPTION OF INPUT-OUTPUT EQUIPMENT 5.2.1 General

Information transfer between a computer and a person is generally through magnetic or paper tapes, card machines, typewriters, visual displays, and line printers. The automatic inputs of the AN jFSQ-7 are all-electronic equipments which translate information from the form in which it appears in the telephone line receiver (serial pulses) to the form used in the com-puter (parallel pulses).

5.2.2 Tapes and Tape-Handling Equipment 5.2.2.1 General

There are two types of tapes available for use with digital computer systems, paper and magnetic. Both types can be used for either input or output functions.

Each type of tape has its own distinctive processing equipment and the tapes are not interchangeable. A paper tape must be used with a paper punch and

reader, and magnetic tape must be used with equipment designed for magnetic tape preparation and processing.

5.2.2.2 Paper Tape Equipment punch arrangement. Normally a computer-prepared tape is an output procedure and a keyboard prepared tape is an input procedure. Paper tape with the associated paper-tape punch and reader is shown in figure 3-92.

The tape reader converts the punched paper-tape code into electric impulses by means of a photo-electric system or by sensing the pattern of hole-no hole with brushes.

The paper-tape reader interprets the punched tape and can be linked to a printout device as well as to the information processing (although it is less expensive than a magnetic tape system) and is generally used with a special purpose computer solving scientific prob-lems of a fixed type.

5.2.2.3 Magnetic Tape and Tape-Handling Equipment

Magnetic tape usually is a coated plastic tape about liz-inch wide similar to the tape used in home style tape recorders. The coating varies with the commercial pro-cesses used to manufacture tape. The coating has mag-netic properties, that enable the tape to be magnetized in discrete units (very small magnetized spots).

Information is represented in the form of a pattern of magnetic bits. In one form of tape recording, a mag-netized spot or bit may represent a binary one; a non-magnetized spot on the tape may represent a binary zero. A more common system of writing on tape requires that both l's and O's be expressed as magnetized bits.

This is accomplished by recording l's with one north-south magnetic alignment and O's with north-south-north alignment. A large amount of information can be stored 125