LARGE-SCALE STORAGE AND MEMORY
5.2 DESCRIPTION OF INPUT-OUTPUT EQUIPMENT .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
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PAPER TAPE PUNCH PAPER TAPE READER
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on a length of tape. A typical tape is about 2,000 feet in length and has a word density of 41 computer words per inch.
Information may be transferred to a magnetic tape by means of special typewriters, by card-to-tape con-verters, by card machines, from magnetic drum, or di-rectly from a computer.
Tape-handling equipment consists of a tape drive with associated electronic reading and writing circuitry.
A typical tape drive is shown in figure 3-93.
If a program has been coded and is ready for translation into a form of information usable in a com-puter, the first step in the procedure is "to write" the program on the tape using the equipment available in a given system. This equipment may be a computer or card machine. When the information is on the tape, the reel of tape is placed in a tape drive unit. Then, the information can be read by the read-write head of this 'mit and the pulse pattern transferred to the computer.
Ttapes and tape-handling equipment may also be used to receive and record outputs from the compwter.
The outputs are operationally processed from the com-puter to the tape unit. Generally the information is left on the magnetic tape in its magnetic form since it will probably be used again by the computer and there is no need for human monitoring (no printout is necessary).
Sometimes a common program is stored on tape so that when it is needed again it will be very easy to insert.
When human monitoring of the output is necessary it is often advantageous to record the output on tape and then use an auxiliary device (entirely separate from the computer) to print the results from the tape. This sys-tem permits a very high speed tape output which can be monitored.
Tapes and the associated equipment are generally used as large-capacity slow-access memory storage. They may be considered 10 equipments since they are used to initially load information into the computer. As storage unit, tapes are memory type equipments, slow in rela-tion to the other memory units.
5.2.3 Card-Handling Equipment 5.2.3.1 General
The term card machines includes all units of a card handling system that uses the holes punched in paper cards to represent information. Such a system must be capable of punching information on cards and reading the information from the punched cards and printing it in a form that can be directly read without further decoding. A card-handling system implies at least three units; a card punch, a card reader, and a printer.
There are many possibilities of coding information
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Card·Handling Equipment 5.2.3.1-5.2.3.4
figure 3-93. Magneflc Tape Drive Unit on cards using numeric or alphanumeric codes. Among the more important codes are the binary and the Hol-lerith.
5.2.3.2 Cards and 'Card-Punch Equipment A typical card (fig 3-94) is of fixed dimensions and is made of a specified quality of paper. A card may be of varying format in accordance with the best tech-niques for translating information from the card to the computer of any given computer system. The card punched in Hollerith code is of one definite format which, despite disadvantages, is suited for use with mechanical computing equipment. Another similar card, arranged in other format, is the binary card; this is suited to electronic computing equipment.
The equipment used to manually transfer informa-tion onto a card is a card punch. A manual card punch is an electromechanical device which punches
informa-tion on cards and prints out the informainforma-tion on the top of the cards. The punching operation is performed at a keyboard, similar to a standard typewriter key-board, by an operator. A typical example of a manual card punch is illustrated in figure 3-95. This particu-lar card punch also performs the additional function of reading the punched cards and converting the informa-tion expressed into a pulse-no pulse pattern for direct computer input. This type of punch is called a com-puter-entry punch. First, the card is punched; then the card is automatically sent to the reading station. At the reading station mechanical feelers sense the hole-no-hole pattern and generate voltages corresponding to this pattern, which in turn are fed to the computer.
Such a system allows the operator to check the card punches before the information is actually entered in the computer.
A card punch for transferring outputs from the computer to cards is illustrated in figure 3-96. This card punch is operated by the computer through the memory. The computer generates voltages which oper-ate punch-selecting electromagnets. When the punches operate, they punch out a card-hole pattern correspond-ing to the computer output information. No manual operation is possible. The computer-operated card punch is faster than the manual operated punch; the output punch can process about 100 cards per minute while the manual-operated punch is limited to the skill of the operator. A processing of about 3 cards per minute is within normal operator capabilities.
In most computers it is possible to punch informa-tion on cards in any of several codes. This may be a built-in feature or, if not, it may usually be accom-plished by special programming techniques.
5.2.3.3 Card Reader
The card reader shown in figure 3-97 is used to transfer information from punched cards into the Cen-tral Computer. The card reader is directly linked to the computer. Cards may be read at the rate of about 250 cards per minute. Reading is accomplished by contact with brushes which sense holes in the card and com-plete an electrical contact; holes in the cards become pulses and the intact area becomes the no-pulse in the binary code arrangement. The reader can be used to process information from cards directly to the memory unit of the computer. This information is available for use in the computer operation or for transfer to mag-netic tape for storage.
5.2.3.4 Line Printer
A line printer records output information, usually in alphanumeric form (fig. 3-98). The term line desig-nates that the printer is capable of printing a line of characters at a time.
Printers vary in speed of the printout from about 121
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Figure 3-94. Card Arranged in Hollerith Code Format 100 lines per minute to over 1,000 lines. The number
of characters per line also varies. The printer in the figure above can print out 150 lines per minute, 64 characters per line.
The exact technique of how the printing is accom-plished is not within the scope of this manual. In gen-eral the computer generates a pattern of voltages which are used to energize electromagnets. These electromag-nets than select the proper letter or number on a type-wheel and the printer prints. The printer illustrated in figure 3-98 prints one line at a time by the simultane-ous positioning of the type wheels (120 in number).
Each typewheel is not positioned in every line of print-out-only those 64 typewheels which can be selected within the cycle of line printout are used.
5.2.4 Typewriter
In some systems, typewriters are available for trans-ferring input and output data into and out of the mem-ory element of the Central Computer. These typewriters have an alphanumeric keyboard and may be manually and computer operated. When typing inputs, typewriters are manually operated and transmit one character at a time to the Input System. The keyboard character is translated into coded electrical pulses for entry into the memory by means of contacts on each key. Manual op-eration is a relatively slow input method and is usually restricted to inputs of a local nature in a computer system with a fixed program. Outputs are typed out one character at a time under computer control and selec-tion. The outputs also are transmitted from the memory.
During output operation the 10 typewriter is oper-ated by a series of electromagnets and solenoids
mount-ed beneath the keyboard. The magnets and solenoids automatically actuate keyboard functions of the type-writers, including carriage return, spacing, tabulation, ribbon color control, and others. When used as input devices, electrical impulses are transmitted from the typewriter by depressing a key. These electrical impulses may be generated in a coded pulse-no-pulse pattern by a preset action of the key in relation to a group of switches.
5.2.5 Visual Displays
Information may be transmitted from a digital com-puter and displayed visually in a direct-read form. The equipment used to display such output information is generally known as visual displays. A typical example of a visual display equipment is shown in figure 3-99.
Some display a picture similar in physical appearance to a television picture of printed or pictorial informa-tion. Other display outputs may be merely graphical, such as might be seen on the usual cathode-ray oscil-loscope.
The main component of a display equipment is a cathode-ray tube (figure 3-99). The special purpose tubes such as those used in the AN/FSQ-7 have pro-visions for writing actual alphabetic characters. Figure 3-100 shows a simplified diagram of a typicial display tube. Writing on the viewing screen is accomplished by forming a character and positioning the character on the tube face. Characters may be generated by a stencil-ing process; that is, the electron beam is directed through a selected aperture in a character-forming ma-trix and directed by electrostatic deflection plates to a selected position on the tube face. The face of the tube
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Fig. 3-95
Figure 3-95. Computer Entry Punch is phosphor-coated. The phosphor emits a blue flash
when illuminated by a writing beam, followed by a yellowish afterglow which persists long enough for human perception. In some display systems, it is pos-sible to retain the character on the tube face by using another beam of electrons.
Information in binary-coded pulse form is trans-mitted from the storage element of the computer or from the Input System to the display equipment. There, it is converted to analog deflection voltages which gen-erate the desired visual displays. Since the information on the tube face does not persist for a long period of 129
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Figure 3-96. Computer-Operated Card Punch
time, it is sometimes desirable to record this informa-tion in a more permanent form. Camera systems are available which automatically photograph the display tube face and process the film to provide a positive transparency. When required, the transparency can be projected on a screen and the information is visually available for as long as required. Other information recording systems photograph the information on the display tube face and project the images on sensitized paper where the information is reproduced.
5.2.6 Other Input-Output Equipment
The 10 equipments discussed in the preceding para-graphs are commonly identified with general purpose digital computers. Possible types of 10 devices associ-ated with special purpose computers are limited only by the capability of any device to transmit or to receive information in a form that can be converte4 for use in a digital computer.
Input information can be transmitted from teletype machines, telemetering devices, analog computers, and even by human voice. In some way, this information must be converted to a pulse no-pulse binary number
Figure 3-97. Card Reader
code, after which it is compatible for transmitting into the computer system as data in a specific problem.
The results of computer computation can be trans-lated into a form that can be transmitted to guided missiles, control systems, and wide-spread inventory and business offices. The devices used to transmit computer results are teletype systems, telephone lines, radio, and so forth. These devices may be directly linked to the computer system and the outputs require no additional processing by human operators. A dramatic type of output is the speech output from the computer. This technique is termed speech communication with the computer and has been used in diagnostic troubleshoot-ing for locattroubleshoot-ing causes of failure.
The choice of 10 devices for special purpose com-puters depends on the sources of information for the solution of specific problems. These sources are some-times termed data-links. The digital computers are not restricted to accepting information only from the tradi-tional tapes, card-machines, and keyboards. They will use data from any source as long as the data is trans-lated into the binary code of pulse no-pulse.
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T .0. 31 P2-2fSQl-2figure 3-98. Line Printer
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Fig. 3-98
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Figs. 3-99 & 3-100
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CHARACTER MATRIX