3.1 THE LANGUAGE USED BY DIGITAL COMPUTERS
The task of a digital computer is to process data, expressed in the form of digits, by performing certain predetermined arithmetic and control operations on the data. These operations are predetermined by a set stored program computers, however, the instructions are expressed in the form of digits. That is, each the computer. These physical conditions-voltages, cur-rents, etc., represent the digits. The physical conditions interact to produce a set of conditions that represent digits expressing the solution to a problem. Thus, the
"language" used by computers consists ultimately of specific physical conditions in its components. Conse-quently, all data and instructions fed to a computer must be represented by specific physical conditions in the computer. For example, if the digits 0, 1, 2, 3, and 4 are to be presented to a digital computer, they must be presented as five separate physical conditions that can be set up in the components of the computer. of digits. Digits representing instructions to the com-puter for operating on input data could be fed into a
The preceding description is extremely simplified and not necessarily based on any system in common use. It does illustrate, however, the type of "language"
that a digital computer "understands." Figure 1-5 gives an idea of the fundamental nature of information the de-energized relay condition.
3.2 DIGITAL-COMPUTER ELEMENTS
not gain any information by multiplying (processing)
UNCLASSIFIED
9Data Processing 3.2.1.1-3.2.1.3
UNCLASSIFIED T.O. 31P2-2FSQ7-2
PART 1 CH 3
DATA INPUT LINES
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4
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2 ADDER 2 DATA OUTPUTLINES
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I I0 0
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= VOLTAGE PULSE LI NES REPRESENT DIGITSc: C
0 I 2 3 4
CONTROL
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Figure J -5. Numbers and Control Instructions Represented in the Form of Voltages the data, although it is admittedly in a form more
suit-able for such purposes as comparison with other num-bers, adding to other numnum-bers, etc. It should always be kept in mind that data processing machines generate, no new information even though their processing re-sults in much greater usability of the existing data. It should also be remembered that the operator or pro-grammer instructs the machine to perform every re-quired step. The machine does not think-all of its op-erations and decisions must be built or programed into it by human effort.
3.2.1.2 Examples of Simple Data Processing A man who processes data does so by following an exact set of rules, although he may not always be conscious of the fact. In making up a payroll, for ex-ample, a paymaster performs a series of predetermined operations which may be written down in a check-list which he must follow. The operations governed by the check-list and their sequence may be as follows:
1. Receive and store (write down) necessary data such as:
a. Number of hours worked by each employee b. Pay rates for each employee
c. Deductions from gross pay for each employee 2. On data stored for each employee, perform
arithmetic operations such as:
a. Multiply hours by hourly pay rate, write down partial products, and add partial prod-ucts for complete product
b. Multiply the sum obtained in operation a by a tax rate
c. Subtract the product obtained in operation b from the product obtained in operation a
3. Make available, in a useful form, the results ( output) of the preceding operations (1 and 2).
Throughout the task of making up a payroll, an efficient paymaster would perform only those operations required by the rules of the task. He would not, for example, add up the ages of all the employees, even if this data appeared on the original documents re-ceived. On the other hand, the paymaster would oper-ate on all the data necessary for the task, and he would perform all necessary operations, as determined by the rules of the task.
Hence, to perform his work properly a paymaster must have some means of storing the required data and the appropriate instructions (such as paper, charts, tables, etc.). Morever, he must be able to extract data as needed and perform arithmetic operations in proper sequence. Finally, he must have means of making avail-able in useful form the results of the operations-for example, a means of making out pay checks.
3.2.1.3 Machine Requirement for Data Processing
If the paymaster were making out the payroll on a computing machine, the machine would require facil-ities for:
a. Receiving necessary data b. Storing the data
c. Controlling, by the rules of the task, the selec-tion of data to be operated on and the proper sequence of operations
d. Performing required arithmetic operations e. Making available in useful form the results of
the operations
10 UNCLASSIFIED
PART 1 ele-ments required by typical digital computers. The follow-ing paragraphs describe these elements and explain the tasks performed by each. Notice the similarity between corresponding computer operations and human oper-ations, and remember that all steps originate with the the input element: it provides one-way communication from the outside world to the computer. Data and computer could work with it. The input element usually performs this function of translating terms understand-able to the outside world to those usunderstand-able by the element may include facilities for converting the results of the computer's operations into the form of output data best suited to the user of the machine. Thus, the answer to the problem might enter the output element in the form of binary electrical pulses. The output ele-ment may then convert these pulses to voltages that operate an electrically operated typewriter or a print-ing machine to print the final answer. (See figure 1-7.) arithmetically must enter this part of the computer. Like-wise, most instructions determining what computations are to be performed must control the arithmetic
Storage Element 3.2.4-3.2.5
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PART 1 CH 3
VOLTAGES FROM OTHER ELEMENTS OF COMPUTER
TYPICAL FOR M OF SOLUTION TO PROBLEM
OUTPUT ELEMENT
TYPICAL VOLTAGE FORM OF PROBLEM SOLUTION AS REQUIRED
{TO OTHER OUTPUT, DEVICES, SUCH AS BELLS, TELEVISION SCREENS}
Figure 1-7. Output Element - This Element Converts Computer's Answer to the Problem into Form Usable by External Output Devices
DATA TO BE OPERATED ON ARITHMETICALLY
CONTROL TELLING WHAT TYPE OF ARITHMETIC TO PERFORM
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ARITHMETIC ELEMENT
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SOLUTIONS TO ARITHMETIC PROBLEMS
CONTROL ON WHAT IS TO BE DONE WITH SOLUTIONS TO THE ARITHMETIC PROBLEMS
Figure I -8. Arithmetic Element - Data Enters and Is Processed by this Element
Theoretically, it would be possible to build an arithmetic element which could perform most mathe-matical operations directly, just as a man performs them. This however, would require a very large and complicated arithmetic device and, consequently, is never done. Instead, the arithmetic element is usually designed to perform only a few basic operations such as addition, subtraction, multiplication, and division.
(Three of these four operations are usually only an adaptation of either addition or subtraction.) If an arithmetic device can perform either addition or sub-traction, and a few other simple operations, it can be made to perform almost any other mathematical oper-ation by simply breaking the operoper-ation down into its fundamental operations. This is the way in which the arithmetic element is made to do the more complex mathematical operations that are often required.
The arithmetic operations in a high-speed machine such as AN/FSQ-7 and AN/FSQ-8 must be accomplis~ed
very quickly. Entire series of operations must be com;
pleted in a few microseconds (usec). This speed cannot be attained by mechanical or electro-mechanical devices (such as relays) but can be attained by electronic circuits. Electronic circuits for performing arithmetic operations are described in Part 3.
3.2.5 Storage Element
As stated in paragraph 2.3.2, operations in a digital computer are carried out in step-by-step fashion. For this reason, some of the information fed into a com-puter must be stored for indefinite periods prior to actual usage. The facilities required for storing informa-tion in a computer are included in the storage element.
Information fed into a computer is of three kinds:
a. Particular items of data to be processed b. Instructions for performing the particular
data-processing operations required (the program) c. Reference data
Reference data-(c) above-must sometimes be stored for indefinite periods. For example, if the com-puter is used in the air-defense system, the reference data will include ballistic tables and Hight plans of friendly aircraft. Such data are used over and over for successive problems. It would be impractical to feed this same information into the computer all over again for each new problem. If the storage element of the computer can retain such data indefinitely and quickly select individual items each· time they are needed, prob-lems can be solved much faster. Indeed, without fast, automatic, and reliable insertion and extraction of data
12 UNCLASSIFIED
PART 1 hand-operated calculators and reference tables.
Another type of information that can be stored is input data for each new problem is accordingly reduced.
The basic characteristic of an information storage medium is that it has at least 2 stable states. For
Figure 1-9. Storage Element - Possible Address and Contents Correlation
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rotating drum coated with a magnetic material. There are also other storage devices, such as magnetic cores and cathode-ray tubes (see Part 3).
All storage elements have some basic characteris-tics that are similar. They always contain a number of perform them. For all desired processing operations, moreover, the results of the arithmetic operations must be routed to the appropriate storage or output loca-tions. Also, the transfer of all output data to the out-put element and, finally, to the user must be properly controlled to ensure the required sequence of informa-tion.
The entire sequence of operations by the computer is predetermined by the program (and the construction of the computer) for the data-processing task. The pro-gram, coded in the digital language used by the com-puter, is inserted through the input element, to be stored at specific addresses in the storage element. The element for interpreting and carrying out instructions contained in the program is the control element (see fig. 1-10).
By its interpretation of the program, the control element governs the flow of data and the sequence of operations performed by the computer. In a high-speed machine such as the AN /FSQ-7, special electrical cir-cuits provide the required control. These circir-cuits re-spond to electrical signals representing the digits that
CONTRO L TO
Figure 1-10. Typical Instructions from Control Element
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