Operational Concepts

NEETS MODULE 22-Digital Computing

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1 OPERATIONAL CONCEPTS

Learning Objectives

After you finish this chapter, you should be able to do the following: 1. Describe the history of computers. 2. Describe how computers are classified. 3. Explain how digital computers have changed during each generation. 4. Describe the practical applications of digital computers in the Navy. 5. Describe the initial steps needed to use a microcomputer. 6. Explain storage media handling, backups, and the threats to storage media. 1.1 INTRODUCTION Digital computers are used in many facets of today's Navy. It would be impossible for one NEETS module to cover all the ways they are used in any depth. A few of these ways are covered later in this chapter.

The purpose of this module is to acquaint you, the trainee, with the basic principles, techniques, and procedures associated with digital computers. We will use a desktop (personal) computer for most of the examples. Personal computers should be more familiar to you than the large mainframes, and the operating principles of personal computers relate directly to the operating principles of mainframe computers. You will learn the basic terminology used in the digital-computer world. When you have completed these chapters satisfactorily, you will have a better understanding of how computers are able to perform the demanding tasks assigned to them.

If we were to define the word computer, we would say a computer is an instrument for performing mathematical operations, such as addition, multiplication, division, subtraction, integration, vector resolution, coordinate conversion, and special function generation at very high speeds. But the usage of computers goes well beyond the mathematical-operations level. Computers have made possible military, scientific, and commercial advances that before were considered impossible. The mathematics involved in orbiting a satellite around the earth, for example, would require several teams of mathematicians for a lifetime. Now, with the aid of electronic digital computers, the conquest of space has become reality.

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Computers are employed when repetitious calculations or the processing of large amounts of data are necessary. The most frequent applications are found in the military, scientific, and commercial fields. They are used in many varied projects, ranging from mail sorting, through engineering design, to the identification and destruction of enemy targets. The advantages of digital computers include speed, accuracy, reliability, and man-power savings. Frequently computers are able to take over routine jobs, releasing people for more important work; work that cannot be handled by a computer.

1.2 HISTORY OF COMPUTERS The ever increasing need for faster and more efficient computers has created technological advances that can be considered amazing. Ever since humans discovered that it was necessary to count objects, we have been looking for easier ways to do it. Contrary to popular belief, digital computers are not a new idea. The abacus is a manually operated digital computer used in ancient civilizations and used to this day in the Orient (see fig. 1-1). For those who consider the abacus outdated, in a contest between a person using a modern calculator and a person using an abacus, the person using the abacus won.

The first mechanical adding machine (calculator) was invented by Blaise Pascal (French) in 1642. Twenty years later, an Englishman, Sir Samuel Morland, developed a more compact device that could multiply, add, and subtract. In 1682, Wilhelm Liebnitz (German) perfected a machine that could perform all the basic operations (addition, subtraction, division, and multiplication), as well as extract the square root. Liebnitz's principles are still in use today in our modern electronic digital computers. As early as 1919, electronics entered the scene. An article by W. H. Eccles and F. W.

Jordan described an electronic "trigger circuit" that could be used for automatic counting. It was the ECCLES-JORDAN multivibrator which was a little ahead of its time because a trigger circuit is one of many components required to make an electronic digital computer. Modern digital computers use these circuits, known as flip-flops, to store information, perform arithmetic operations, and control the timing sequences within the computer. Figure 1-1 Abacus NEETS MODULE 22-Digital Computing

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Under the pressure of military needs in World War II, the science of electronic data processing made giant strides forward. In 1944, Harvard University developed a computing system known as the Automatic Sequence Controlled Calculator. After the initial design and construction, several improved models were built. Meanwhile, at the University of Pennsylvania, a second system was being developed. This system, completed in 1946, was named ENIAC (Electronic Numerical Integrator and Computer). ENIAC employed 18,000 vacuum tubes in its circuitry; and in spite of these bulky, hot tubes, it worked quite successfully. The first problem assigned to ENIAC was a calculation in nuclear physics that would have taken 100 human-years to solve by conventional methods. The ENIAC solved the problem in 2 weeks, only 2 hours of which were actually spent on the calculation. The remainder of the time was spent checking the results and operational details. All modern computers have their basics in these two early developments conducted at Harvard University and University of Pennsylvania.

In 1950, the UNIVAC I was developed. This machine was usually regarded as the most successful electronic data processor of its day. An outstanding feature of the UNIVAC I was that it checked its own results in each step of a problem; thus eliminating the need to run the problems more than once to ensure accuracy. During the first outbreak of publicity about computers (especially when the UNIVAC predicted the outcome of the 1952 presidential election), the term "giant brain" caused much confusion and uneasiness. Many people assumed that science had created a thinking device superior to the human mind. Currently most people know better. By human standards the giant brain is nothing more than a talented idiot that is wholly dependent upon human instructions to perform even the simplest job. A computer is only a machine and definitely cannot think for itself. The field of artificial intelligence, however, is developing computer systems that can "think"; that is, mimic human thought in a specific area and improve performance with experience and operation. The field of digital computers is still in the growing stages. New types of circuitry and new ways of accomplishing things are continuing to be developed at a rapid rate.

In the military field, the accomplishments of digital computers are many and varied. One outstanding example is in weapons systems. Most of the controlling is done by digital computers. NEETS MODULE 22-Digital Computing

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1.3 CLASSIFICATIONS OF COMPUTERS Computers can be classified in many different ways. They can be classified by the type of technology they use (mechanical, electromechanical, or electronic), the purpose for which they were designed (general purpose or special purpose), by the type of data they can handle (digital or analog), by the amount they cost (from $50 to $10 million and up), and even by their physical size (handheld to room size). We will briefly explain mechanical, electromechanical, and electronic computers; special-purpose and general- purpose computers; and analog and digital computers.

1.3.1 Mechanical Computers Mechanical or analog computers are devices used for the computation of mathematical problems. They are made up of components, such as integrators, sliding racks, cams, gears, springs, and driveshafts. Figure 1-2 shows a typical mechanical computer used by the Navy. These computers are analog in nature, and their physical size depends on the number of functions the computer has to perform. In an analog computer, a continuing input will give a constantly updated output. This being perfect for target information, the Navy uses these analog computers primarily for gun fire control. As systems for naval weapons became more and more complex, the need for a different computer was apparent. The functions that had to be performed had increased the size of the computer to an unreasonable scale.

Figure 1-2 Bulkhead-type mechanical computer NEETS MODULE 22-Digital Computing

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1.3.2 Electromechanical Computers Electromechanical computers came next and differ from mechanical computers in that they use electrical components to perform some of the calculations and to increase the accuracy. Because the electrical components are smaller than their mechanical counterparts, the size of the computer was reduced, even though it performs more functions. The components used to perform the calculations are devices such as synchros, servos, resolvers, amplifiers, servo amplifiers, summing networks, potentiometers, and linear potentiometers. Figure 1-3 shows one of the Navy's electromechanical computers.

These computers are used in gun fire control and missile fire control. Even though they are better than the mechanical computer, they still have their drawbacks. Of prime importance is that they are special-purpose computers. This means they can only be used for one job, dependent on their design characteristics. By today's Navy standards they are still too large, and the maintenance time on them is excessive. The need for a more accurate, reliable, versatile, and smaller computer was recognized. Figure 1-3 Electromechanical computer NEETS MODULE 22-Digital Computing

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1.3.3 Electronic Computers Next came electronic computers. The early electronic computers' mathematical processes were solved by using electrical voltages only, applied to elements such as amplifiers, summing networks, differentiating, and integrating circuits. The weak link in this type of electrical computation was the vacuum tube. To correct this, transistors which consume less power and last longer than vacuum tubes were used in the amplifiers. Through technological research and development, we have progressed from tubes, to transistors, to miniaturized circuits, to integrated circuitry. These advances have made it possible to reduce the size and weight of our computers. Figure 1-4 is an example of one of our modern electronic digital computers.

Figure 1-4 Electronic digital computer NEETS MODULE 22-Digital Computing

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1.3.4 Special-Purpose Computers A special-purpose computer, as the name implies, is designed to perform a specific operation and usually satisfies the needs of a particular type of problem. Such a computer system would be useful in weather predictions, satellite tracking, or oil exploration. While a special-purpose computer may have many of the same features found in a general-purpose computer, its applicability to a particular problem is a function of its design rather than to a stored program. The instructions that control it are built directly into the computer, which makes for a more efficient and effective operation. A drawback of this specialization, however, is the computer's lack of versatility. It cannot be used to perform other operations.

1.3.5 General-Purpose Computers General-purpose computers are designed to perform a wide variety of functions and operations. You will probably use this type of computer. A general-purpose computer is able to perform a wide variety of operations because it can store and execute different programs in its internal storage. Unfortunately, having this ability is often achieved at the expense of speed and efficiency. In most situations, however, you will find that having this flexibility makes this compromise a most acceptable one.

1.3.6 Analog Computers All analog computers are special-purpose computers. They are designed to measure continuous electrical or physical conditions, such as current, voltage, flow, temperature, length, or pressure. They then convert these measurements into related mechanical or electrical quantities. The early analog computers were strictly mechanical or electromechanical devices. They did not operate on digits (in binary notation, either of the characters, 0 and 1). If digits were involved at all, they were obtained indirectly. Your wrist watch (if nondigital); your car's speedometer; and oil pressure, temperature, and fuel gauges are also considered analog computers. The output of an analog computer is often an adjustment to the control of a machine; such as, an adjustment to a valve that controls the flow of steam to a turbine generator or a temperature setting to control the ovens in the ship's galley for baking. Analog computers are also used for controlling processes. To do so, they must convert analog data to digital form, process it, and then convert the digital results back to analog form.

You should know that a digital computer can process data with greater accuracy than an analog computer, but an analog computer can process data faster than a digital computer, in some systems. Some computers combine the functions of both analog and digital computers. They are called hybrid computers. NEETS MODULE 22-Digital Computing

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1.3.7 Digital Computers Digital computers perform arithmetic and logic functions on separate discrete data, like numbers, or combinations of discrete data, such as name, rate, and division. This makes them different from analog computers that operate on continuous data, like measuring temperature changes. We generally use digital computers for business and scientific data processing. The following are examples: Accounting—Computers are idea l for keeping payroll records, printing paychecks, billing customers, preparing tax returns, and taking care of many of the other accounting tasks in an organization.

Recordkeeping—Computers can record information like inventories and personnel files. They can also keep track of books checked out of a library. Airline ticket counters are much more efficient than they used to be, thanks to centralized reservation computers that can be reached over the telephone lines. Industrial Uses—Industrial computers s ave considerable time and reduce waste by efficiently performing hundreds of industrial tasks, ranging from filling sales orders and routing parts to various locations on an assembly line, to designing earthquake-resistant structures, and controlling an entire oil refinery.

Science—The research and development applications are the most numerous. Digital computers are being used to do lengthy and complicated mathematical calculations millions of times faster than human beings. They are also used to collect, store, and evaluate data from experiments, analyze weather patterns, forecast crop statistics, and, believe it or not, design other computers. Word Processing—Remember, these words were typed into a desktop computer! Word processing is among the most common applications for personal computers. If you have not discovered the advantages of computer writing, it's time to visit a computer dealer for a personalized demonstration.

None of this work could be performed by a computer without first instructing the computer how to do it by means of a list of instructions called a program. The instructions in the program must be written in one of the languages the computer understands. The most popular generic term for computer programs is software (this is covered in chapter 3). Hardware (covered in chapter 2), of course, refers to the computer and related equipment. It is easy to say that both computer hardware and software are interdependent because neither can perform useful work without the other. Digital computers may be either special or general purpose.

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1.3.8 Accuracy of Computers The fundamental difference between analog and digital computers is that digital computers deal with discrete quantities such as beads on an abacus, notches on a toothed wheel, or electrical pulses, while analog computers deal with continuous physical variables such as electrical voltages or mechanical shaft rotations. Computation with analog computers depends on the relation of information to a measurement of some physical quantity. For example, you can determine the number of boards in a picket fence by either a digital or an analog system as follows. In the digital method (fig. 1-5, view A), you use an adding machine and count the boards one by one. In the analog method (fig.

1-5, view B), you draw a string (marked off in inches for the width of each board including the gap) over the length of the fence, then measure the length of the string. The number of boards may then be determined by dividing the length of string by the number of inches per board. Figure 1-5A Digital computation NEETS MODULE 22-Digital Computing

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The accuracy of an analog computer is restricted to the accuracy with which physical quantities can be sensed and displayed. This, in turn, is related to the quality of the components used in constructing the computer; for example, the tolerance of electrical resistors or mechanical shafts and the quality of the output equipment. In an analog computer, for example, if the constant is represented by a voltage, it probably could be read only to the third decimal place. On the other hand, the accuracy of a digital computer is governed by the number of significant figures carried in the computations. This, in turn, is determined by the computer's design. In a digital computer, the number of decimal places in the constant could be many, depending on the design of the computer processing unit. The digital computer is, therefore, capable of higher precision and accuracy. However, a computer, regardless of its accuracy, would do you no good if the wrong one were chosen for a given task.

Most of the computer systems you will work with will be general-purpose digital computers. The remainder of this module will be about general-purpose digital computers. Figure 1-5B.— Analog computation NEETS MODULE 22-Digital Computing

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Q-1. How are computers classified? Q-2. Mechanical computers are considered to be of what type? Q-3. The Navy uses analog computers primarily for what purpose? Q-4. How do electromechanical computers differ from the mechanical computers? Q-5. In electronic computers, vacuum tubes were replaced by transistors and transistors have been replaced by what device? Q-6. A computer that is designed to perform a specific operation and usually satisfies the needs of a particular type of problem, is said to be what type of computer?

Q-7. Rather than using a stored program, a special-purpose computer's applicability to a particular problem is a function of what? Q-8. What is a drawback to the special-purpose computer? Q-9. A general-purpose computer is designed for what purpose? Q-10. How is a general-purpose computer able to perform different operations? Q-11. In a general-purpose computer, the ability to perform a wide variety of operations is achieved at the expense of what capabilities? NEETS MODULE 22-Digital Computing

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Q-12. All analog computers are what type of computers? Q-13. What are analog computers designed to measure? Q-14. Early analog computers were what type of devices? Q-15. What are computers called that combine the functions of both analog and digital computers? Q-16. Digital computers are generally used for what purposes? Q-17. What is the fundamental difference between analog and digital computers? Q-18. How is the accuracy of an analog computer restricted? Q-19. A constant represented by a voltage can be read to what decimal place?

Q-20. The accuracy of a digital computer is governed by what factor? Q-21. In a digital computer, what does the number of decimal places in the constant depend on? Q-22. You will most likely be working with what type of computer? NEETS MODULE 22-Digital Computing

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1.4 DIGITAL COMPUTER GENERATIONS In the electronic computer world, we measure technological advancement by generations. A specific system is said to belong to a specific "generation." Each generation indicates a significant change in computer design. The UNIVAC I represents the first generation. Currently we are moving toward the fourth generation. 1.4.1 First Generation The computers of the first generation (1951-1958) were physically very large machines characterized by the vacuum tube (fig. 1-6). Because they used vacuum tubes, they were very unreliable, required a lot of power to run, and produced so much heat that adequate air conditioning was critical to protect the computer parts. Compared to today's computers, they had slow input and output devices, were slow in processing, and had small storage capacities. Many of the internal processing functions were measured in thousandths of a second (millisecond). The software (computer program) used on first generation computers was unsophisticated and machine oriented. This meant that the programmers had to code all computer instructions and data in actual machine language.

They also had to keep track of where instructions and data were stored in memory. Using such a machine language (see chapter 3) was efficient for the computer but difficult for the programmer. Figure 1-6 First generation computers used vacuum tubes NEETS MODULE 22-Digital Computing

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1.4.2 Second Generation The computers of the second generation (1959-1963), were characterized by transistors (fig. 1-7) instead of vacuum tubes. Transistors were smaller, less expensive, generated almost no heat, and required very little power. Thus second generation computers were smaller, required less power, and produced a lot less heat. The use of small, long lasting transistors also increased processing speeds and reliability. Cost performance also improved. The storage capacity was greatly increased with the introduction of magnetic disk storage and the use of magnetic cores for main storage. High speed card readers, printers, and magnetic tape units were also introduced. Internal processing speeds increased. Functions were measured in millionths of a second (microseconds). Like the first generation, a particular computer of the second generation was designed to process either scientific or business oriented problems but not both. The software was also improved. Symbolic machine languages or assembly languages were used instead of actual machine languages. This allowed the programmer to use mnemonic operation codes for instruction operations and symbolic names for storage locations or stored variables. Compiler languages were also developed for the second generation computers (see chapter 3).

Figure 1-7 Second generation computers used transistors NEETS MODULE 22-Digital Computing

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1.4.3 Third Generation The computers of this generation (1964-1970), many of which are still in use, are characterized by miniaturized circuits. This reduces the physical size of computers even more and increases their durability and internal processing speeds. One design employs solid-state logic microcircuits (fig. 1-8) for which conductors, resistors, diodes, and transistors have been miniaturized and combined on half-inch ceramic squares. Another smaller design uses silicon wafers on which the circuit and its components are etched.

The smaller circuits allow for faster internal processing speeds resulting in faster execution of instructions. Internal processing speeds are measured in billionths of a second (nanoseconds). The faster computers make it possible to run jobs that were considered impractical or impossible on first or second generation equipment. Because the miniature components are more reliable, maintenance is reduced. New mass storage, such as the data cell, was introduced during this generation, giving a storage capacity of over 100 million characters. Drum and disk capacities and speed have been increased, the portable disk pack has been developed, and faster, higher density magnetic tapes have come into use. Considerable improvements were made to card readers and printers, while the overall cost has been greatly reduced. Applications using online processing, real-time processing, time sharing, multiprogramming, multiprocessing, and teleprocessing have become widely accepted. More on this in later chapters.

Figure 1-8 Third generation computers used microcircuits NEETS MODULE 22-Digital Computing

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Manufacturers of third generation computers are producing a series of similar and compatible computers. This allows programs written for one computer model to run on most larger models of the same series. Most third generation systems are designed to handle both scientific and business data processing applications. Improved program and operating software has been designed to provide better control, resulting in faster processing. These enhancements are of significant importance to the computer operator. They simplify system initialization (booting) and minimize the need for inputs to the program from a keyboard (console intervention) by the operator.

1.4.4 Fourth Generation and Beyond The computers of the fourth generation are not easily distinguished from earlier generations, yet there are some striking and important differences. The manufacturing of integrated circuits has advanced to the point where thousands of circuits (active components) can be placed on a silicon wafer only a fraction of an inch in size (the computer on a chip). This has led to what is called large scale integration (LSI) and very large scale integration (VLSI). As a result of this technology, computers are significantly smaller in physical size and lower in cost. Yet they have retained large memory capacities and are ultra fast. Large mainframe computers are increasingly complex.

Medium sized computers can perform the same tasks as large third generation computers. An entirely new breed of computers called microcomputers (fig. 1-9) and minicomputers are small and inexpensive, and yet they provide a large amount of computing power. Figure 1-9 Fourth generation desktop (personal) computer NEETS MODULE 22-Digital Computing

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What is in store for the future? The computer industry still has a long way to go in the field of miniaturization. You can expect to see the power of large mainframe computers on a single super chip. Massive data bases, such as the Navy's supply system, may be written into read-only memory (ROM) on a piece of equipment no bigger than a desktop calculator (more about ROM in chapter 2). The future challenge will not be in increasing the storage or increasing the computer's power, but rather in properly and effectively using the computing power available. This is where software (programs such as assemblers, report generators, subroutine libraries, compilers, operating systems, and applications programs) will come into play (see chapter 3). Some believe developments in software and in learning how to use these extraordinary, powerful machines we already possess will be far more important than further developments in hardware over the next 10 to 20 years. As a result, the next 20 years (during your career) may be even more interesting and surprising than the last 20 years.

Q-23. Technological advancement is measured by what, in the electronic computer world? Q-24. What does each generation of computer systems indicate? Q-25. What were computers of the first generation characterized by? Q-26. How did vacuum tubes cause a problem for first generation computers? Q-27. In first generation computers, internal processing functions were measured by what division of time? Q-28. The software (computer program) used on first generation computers was what type? Q-29. How were processing speed and reliability increased in second generation computers?

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Q-30. In second generation computers, how was the storage capacity greatly increased? Q-31. With improvements in software, what kind of computer languages could be used on second generation computers? Q-32. What do the smaller circuits in third generation computers allow for? Q-33. On third generation computers, what results are gained by faster internal processing speeds? Q-34. The data cell had a storage capacity of how many characters? Q-35. What type of applications were most third generation computer systems designed to accomplish?

Q-36. What type of computers are small and inexpensive yet provide a lot of computing power? Q-37. What does the acronym ROM stand for? Q-38. What will be one of the future challenges involving computer power? Q-39. What term is used for programs such as assemblers, compilers, and operating systems? NEETS MODULE 22-Digital Computing

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1.5 USES OF A DIGITAL COMPUTER In the modern computer world of today, the uses of the digital computer are almost as limitless as a person's imagination. New and better programs are being written everyday for easier and greater uses. Consider how many mathematicians it would take to put an astronaut in orbit around the moon, but it only takes one computer. Think back to the days without word processing when a document had to be retyped entirely when any changes were needed. Think back to the days of using an adding machine to prepare and revise budgets and accounting reports. Let's look at three of the primary uses of general- purpose digital computers in the Navy: word processing, accounting/recordkeeping, and work center uses.

1.5.1 Word Processing One of the more widespread uses of the computer is word processing. The word processor can be considered a typewriter with a display screen. To the hundreds of thousands of word processor users, the computer is nothing more than a typewriter. Both have keyboards, and both have a mechanism for making the image of the character you strike on the keyboard appear on some type of visual medium. When using an electric typewriter, the process is strictly mechanical. When you press the key, it causes the type face to strike the paper, and in so doing, it leaves an impression. In the computer, the process is more indirect. A program stored in the computer's memory causes a visual representation to appear on a crt (cathode-ray tube) or at a printer. However, from the view point of the user, the result is the same, a printed document.

The great advantage of computers over typewriters is in correcting errors. In the past, correcting a document with a typewriter has meant typing it all over again. Since computers allow the movement of information from one part of memory to another, it is possible to make many changes on a document, and print the result. If the document is still not correct, only the changes need to be entered. The use of computers in this particular way came to be known as word processing. A further breakthrough came with the development of word-processing application programs for microcomputers. These programs cost a fraction of their office machine counterparts, and could be run on general-purpose microcomputers. This was unique because general-purpose microcomputers could be used for functions such as spreadsheets, data base management systems, and programming in common computer languages.

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The Navy saw the obvious uses to which microcomputers using the word processing programs could be put. Some of these are manuscript writing, memorandum writing, identification-card application filing, and recordkeeping. 1.5.2 Accounting and Recordkeeping There are virtually unlimited applications for the computer in today's modern business world, from basic accounting functions to controlling the manufacture of products, and of course, keeping records of these actions. Six standard systems dealing with accounting applications are widely accepted. These systems are (1) order entry; (2) inventory control; (3) accounts receivable; (4) accounts payable; (5) general ledger; and (6) payroll.

(Figure 1-10 shows a simplified flowchart of payroll.) The area of recordkeeping has two requirements, legal and audit. The Navy has included similar functions in its Shipboard Non-Tactical ADP Program for work center use. Figure 1-10 Programming flowchart used to build a payroll program NEETS MODULE 22-Digital Computing

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1.5.3 Work Center Uses (Snap II) Every Navy rating has the responsibility for some element of ship's maintenance. And for every rate, recordkeeping has been a "tough nut to turn," an administrative chore that goes along with the work to be done, but takes a "back burner" position to the physical maintenance of the ship and equipment. Today, aboard some ships and soon aboard most, much of that hassle will be done with a SNAP. The Navy has looked at the paperwork blizzard of recordkeeping responsibility of the essential records and reports that must be generated, and has offered relief to the fleet.

This is in the form of S-N-A-P, which stands for Shipboard Non-Tactical ADP Program. SNAP II is a modern shipboard computer system designed to support shipboard and intermediate level maintenance, supply, financial, and administrative functions. If this sounds confusing, it really isn't, for the systems are designed to be user-friendly; that is, operating instructions are written in everyday English. Figure 1-11 shows the AN/UYK- 62 (V) Data Processing Set. This is the SNAP II computer and its associated hardware. Figure 1-11 AN/UYK-62 (V) Data Processing Set (SNAP II) NEETS MODULE 22-Digital Computing

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Over the next 3 years, new functions will be added to SNAP to support more of the ship's administrative workload. Pay, personnel, food service, ship's store, PMS, training, medical and dental data are all to be added to SNAP systems. The SNAP concept is to take the power of the modern computer, the ability to process information, and put that power in the hands of the work center sailors. The sailors can use the system to reduce the labor associated with the paperwork function. User terminals are placed in the different work centers for use by the work center supervisor. Each work center has a different access code. This access code or password prevents unauthorized entry into the main computer's program. Different levels of entry are also defined. The levels depend on a work center's need.

Information stored in the computer for a typical work center normally has the following items that can be updated by the work center supervisor. COSAL (coordinated onboard ship/shore allowance list) is a listing of the repair parts that are allowed to be kept onboard ship, at all times. APL (allowance parts list) is the reference for stock numbers, part numbers, and quantity allowed onboard for a specific system. EIC (equipment identification code) identifies a system, sub-system, or equipment. SHIP'S FORCE WORK LIST is a listing of all work to be performed by a certain work center during a given time period. CSMP (current ship's maintenance projects) provides shipboard maintenance managers with a consolidated listing of deferred maintenance to manage and control its accomplishment. These are but a few of the uses of SNAP II that can be updated by the work center supervisor.

Although the information is usually viewed on a display screen (cathode-ray tube), printed (hard) copies can be obtained. Today, hard copy output from SNAP can be sent to higher authorities in lieu of written reports. In the future, these hard copy transmittals may be replaced by disks or tapes containing the same data. In some cases, the shipboard computers will have an extra telephone wire to the pier or tender, and information can be exchanged electronically. And there are other important benefits. In practice, the system expedites the storage and retrieval of information the Navy has about its ships. In turn, information that is more accessible means a more timely supply of parts, an improved aid to planners on when and how long to schedule ships' overhauls, and updated information for making decisions whether to place additional or remove unnecessary shipboard equipment. These decisions are now made by laboriously using stacks of printed files. SNAP can sort through these files electronically so Navy planners can make more effective and timely decisions.

SNAP II is a system for unclassified use only at present. This cuts the costs of the installation and many of the physical and electronic security requirements. NEETS MODULE 22-Digital Computing

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Q-40. What is one of the more widespread uses of the computer? Q-41. What is the great advantage of computers over typewriters? Q-42. How are word processing programs used by the Navy? Q-43. How many systems dealing with accounting applications have been widely accepted? Q-44. What does the acronym S-N-A-P stand for? Q-45. For what purposes is the SNAP II system designed? Q-46. What does user friendly mean in computer terms? Q-47. What does a password prevent? Q-48. In the SNAP II system, how are the different levels of entry defined?

Q-49. The work center supervisor can update what items from a user terminal? Q-50. At present what type of classified use is allowed for SNAP II? NEETS MODULE 22-Digital Computing

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1.6 USING A DESKTOP COMPUTER To use a desktop (personal) computer effectively, you'll need to learn about the hardware (the equipment) and the software (the programs). You will also need to know how to handle disks and how to back up programs and data files. So let's assume you have a desktop computer system to use. Its hardware consists of a display screen, a keyboard, a computer, two floppy disk drives (A & B), and a printer. Look at the example in figure 1- 12. You need software (computer programs) to make the computer operate. The first program you need is the operating system. The operating system manages the computer and allows you to run application programs like word processing or recordkeeping programs. So let's begin with the operating system.

Figure 1-12 Typical microcomputer system with display, keyboard, floppy disk drives, and printer NEETS MODULE 22-Digital Computing

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1.6.1 Operating System An operating system is simply a set of programs and routines that lets you and other programs use the computer. A digital computer uses one central set of programs called the operating system to manage execution of other programs and to perform common functions like read, write, or print. Other programs, or you the user, can order the operating system to perform these common functions. These orders are called system calls when other programs use them, or simply commands when you put them through the keyboard.

First, you must load the operating system into the computer so we, and our programs, can use the computer. Remember, in our example, we have a desktop computer with two floppy disk drives, named A and B. 1.6.1.1 Booting the System Each desktop computer has a built-in program called "bootstrap loader." When you turn the computer on, this program tries to load, or "boot," an external operating system from disk, usually from drive A, into the computer's internal memory. Disk drive B is usually used for data file disks. The term boot comes from the idea of pulling yourself up by your bootstraps. The computer loads a little program from the disk that tells it how to load a second, bigger program (the operating system). The operating system then tells it how to load another program (an applications program or utility program) to perform a specific job or function. The first thing you need to learn about using a computer is that computers and their programs are very particular. They require complete accuracy and attention to detail on your part. They are not good at guessing what you meant. You'll quickly learn there are a few things that can go wrong at this point, in which case the computer will give you an error message on the display screen similar to this: Device Error This means the computer is not reading anything in A drive. Check for: 1. No floppy disk in drive A 2. Floppy disk inserted incorrectly in drive 3. Lock handle on drive A not lowered NEETS MODULE 22-Digital Computing

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Another error message you might receive at this time is: No System This means the computer is reading a properly inserted floppy disk, but the disk does not have an operating system on it. Replace the disk with one that does contain the operating system. Once the operating system is properly booted (loaded), you will see a display similar to this: A> You now have what is called a prompt. At this point you can tell the computer what to do next, such as run an application program for example: word processing, accounting, or recordkeeping.

1.6.1.2 Running an Application Program To load an application program into the computer from drive A, you put the disk with the application program in disk drive A. Next you type the name of the program following the operating system prompt (A>). A>WORDPROC This tells the system what program to load and run; in this case Word Processing. The computer then does what the application program tells it. If the application is word processing, the system is ready for you to type a new document, correct an existing document, print a document, and so on. You'll learn more about both the operating system and application programs in chapter 3.

Each application program will have its own set of instructions to follow. In addition to printed documentation, many will include online HELP screens you can display while you are working. These will tell you how to perform a given function or operation. Another area that needs your constant attention relates to handling floppy disks and making backup copies to be sure your work is not lost. NEETS MODULE 22-Digital Computing

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1.6.2 Storage Media Handling and Backup Floppy disks (fig. 1-13) are one means by which you will store data (files that you create) either directly or in backing up the data you store on hard (or fixed) disk. For this reason, and because floppy disks are extremely fragile, you should follow certain guidelines to ensure their proper care and handling. This includes properly labeling and backing up disks. 1.6.2.1 Handling Never touch the exposed surface of a disk. As you know (or will learn), most of the surface of the actual disk is protected most of the time; however, there are areas that are exposed. These areas are the timing hole and the read/write slots. Touching an exposed area can ruin that particular area. If you are familiar with Murphy's Law, you will realize the area you ruin will invariably contain the most important data on that disk.

Figure 1-13 Floppy disk NEETS MODULE 22-Digital Computing

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1.6.2.2 Storage Never bend, fold, or otherwise distort the shape of a disk. Never place heavy objects such as books on top of disks. Store disks in the box they came in, or in filing containers that are specifically designed for storing disks. Try to store disks vertically, but if you do store disks horizontally, do not stack more than 10 disks. 1.6.2.3 Exposure Disks are subject to exposure from magnetic fields, smoke, heat, and sunlight. X-rays may also have a negative effect. MAGNETIC FIELDS.—Disks should never be exposed to anything that could be the source of a magnetic field. Exposure of a disk to a magnetic field could cause the destruction of some or all of the data contained on that disk. Some common sources of magnetic energy are crt's, disk drives, and perhaps the most common, the telephone.

SMOKE.—Smoke can cause buildup on disks and on disk drives. DO NOT SMOKE while you work at a terminal or computer. HEAT AND SUNLIGHT.—Never expose disks to excessive heat or direct sunlight. Either can cause the disks to become warped or distorted so they cannot be used. Disks are made of a plastic material, and if you have ever seen a phonograph record that has been exposed to heat or sunlight, you have some idea of the damage that can result from exposure. Typically, disks will operate only between 10 and 50 degrees Celsius (50 to 120 degrees Fahrenheit). They will accept a relative humidity of 10% to 80%.

X-RAYS.—There is some question about the effect that airport x-ray machines have on disks. It has been the normal experience that the walk-through x-ray machines at airports have no effect on floppy disks; however, this is not to say there will be no effect. It is up to you because these disks contain the data you work with and need. You may not want to take the chance the disks will be affected. 1.6.2.4 Labeling When labeling the outside of a floppy disk, write the label before attaching it to the disk. Never use a pencil or ballpoint pen to write on a label once that label has been attached to a disk. When you use an instrument with a sharp point to write on the label, you can actually etch into the surface of the disk underneath the protective sheath, thereby destroying that disk. If you must write on a label once it has been attached to a disk, use a felt-tip marker.

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1.6.2.5 Data Backup In virtually all computer systems, the possibility exists for errors to occur that accidentally alter or destroy the data stored in the data bases or files. This may occur because of natural disasters, such as fire, flood, or power outages. It may occur through operator error. It may occur through equipment malfunction. It is essential, therefore, to provide a means to ensure that any data lost can be recovered. The most common method is backup files. A backup file is merely a copy of a file. If for some reason the file or data base is destroyed or becomes unusable, the backup file can be used to recreate the file or data base.

Two media are commonly used for backup: disk or tape. Disk—The most common method of creating a backup for a microcomputer is to use a floppy disk and the diskcopy procedure. This is accomplished by using the original data base or file and copying the information onto a blank floppy disk. The instructions for this procedure will be provided with the particular computer and program you are using. Tape—Another method of creating a backup is to use magnetic tape. The information contained on your disk, whether it is a data base or file, can be copied onto a tape. The instructions for this procedure will also be provided with the particular computer and program you are using.

Q-51. What is a central set of programs called that manages the execution of other programs and performs common functions like read, write, and print? Q-52. What is the function of a built-in program called a bootstrap loader? Q-53. When you see the error message NO SYSTEM, what does it mean? Q-54. When an operating system prompt (A>) is displayed on the screen, what do you enter from the keyboard to load an application program? Q-55. If disks are stored horizontally, how many can be stacked? NEETS MODULE 22-Digital Computing

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Q-56. What can exposure to a magnetic field do to the data on a disk? Q-57. What is the temperature range within which a disk will operate? Q-58. What is the most common method to ensure that any stored data lost can be recovered? Q-59. The most common method of creating a backup for a microcomputer is what? Q-60. Other than disk, what is another media used for backup files? 1.7 SUMMARY This chapter has presented information on the history and classification of computers. It introduced you to electronic digital computers, their uses and operation. The information that follows summarizes the important points of this chapter.

Early computers were MECHANICAL or ELECTROMECHANICAL. ELECTRONIC COMPUTERS came into use in the 1940s. ANALOG COMPUTERS are special-purpose computers designed to measure continuous electrical or physical conditions. DIGITAL COMPUTERS are special- or general-purpose computers designed to perform arithmetic and logic functions on separate discrete data. They are generally used for business and scientific data processing. Digital computers have evolved through four generations: vacuum tubes, transistors, miniaturized circuits, and integrated circuits.

WORD PROCESSING is one of the most widespread uses of desktop computers. NEETS MODULE 22-Digital Computing

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ACCOUNTING AND RECORDKEEPING are also major uses of computers. Included are order entry, inventory control, accounts receivable, accounts payable, general ledger, and payroll. The Navy's SHIPBOARD NON-TACTICAL ADP PROGRAM (SNAP) consists of computers used by work center supervisors for logistic and administrative support. This system expedites the storage and retrieval of information the Navy has about its ships. A DESKTOP (PERSONAL) COMPUTER is a microcomputer with at least a display screen, keyboard, floppy disk drive, and printer. It may also have additional devices such as a second floppy or a hard disk drive.

An OPERATING SYSTEM is loaded into the computer to let you and other programs use the computer. It also provides common functions like read, write, and print. You can direct the computer to run an APPLICATION PROGRAM by telling the operating system the name of program to run. Common application programs are word processing, accounting, and recordkeeping. You will probably be using FLOPPY DISKS for data storage and backup. To ensure you don't damage a disk, use care in handling, labeling and storing the disks. NEETS MODULE 22-Digital Computing

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Answers To Questions Q1. Through Q60.

A-1. Technology (mechanical, electromechanical, electronic), purpose (special or general), type of data they handle (analog or digital), cost, physical size (handheld to room size). A-2. Analog. A-3. Gun fire control. A-4. Electromechanical computers use electrical components to perform some of the calculations. A-5. Integrated circuits. A-6. Special-purpose. A-7. Its design. A-8. Lack of versatility. A-9. To perform a wide variety of functions and operations. A-10. By storing different programs in its internal storage.

A-11. Speed and efficiency. A-12. Special-purpose. A-13. Continuous electrical or physical conditions. A-14. Mechanical or electromechanical. A-15. Hybrid computers. A-16. Business and scientific data processing. A-17. Digital computers deal with discrete quantities, while analog computers deal with continuous physical variables. A-18. By the accuracy with which physical quantities can be sensed and displayed. NEETS MODULE 22-Digital Computing

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A-19. Third. A-20. The number of significant figures carried in the computations. A-21. Design of the computer processing unit. A-22. General-purpose digital computer. A-23. Generations. A-24. Significant change in computer design. A-25. The vacuum tube. A-26. They were unreliable, required a lot of power to run, and produced so much heat that air conditioning was needed to protect computer parts. A-27. Thousandths of a second (millisecond). A-28. Unsophisticated and machine oriented. A-29. By the use of small, long lasting transistors.

A-30. With the introduction of magnetic disk storage and the use of core for main storage. A-31. Symbolic machine languages or assembly languages. A-32. Faster internal processing speeds. A-33. Faster execution of instructions. A-34. Over 100 million. A-35. Both scientific and business data processing applications. A-36. Microcomputers and minicomputers. A-37. Read-only memory. A-38. How to properly and effectively use the computing power available. NEETS MODULE 22-Digital Computing

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A-39. Software. A-40. Word processing. A-41. Correcting errors. A-42. For manuscript writing, memorandum writing, identification-card application filing, and recordkeeping. A-43. Six. A-44. Shipboard Non-tactical ADP Program. A-45. To support shipboard and intermediate level maintenance, supply, financial, and administrative functions. A-46. Operating instructions are written in everyday English. A-47. Unauthorized entry into the main computer's program. A-48. Dependent on a work center's need. A-49. COSAL, APL, EIC, SHIP'S FORCE WORK LIST, and CSMP.

A-50. Unclassified. A-51. Operating system. A-52. To load an external operating system into the computer's internal memory. A-53. The computer is reading a properly inserted floppy disk, but it does not have an operating system on it. A-54. The program name. A-55. No more than ten. A-56. Destroy some or all of it. A-57. 10 to 50 degrees Celsius or 50 to 120 degrees Fahrenheit. A-58. Backup files. NEETS MODULE 22-Digital Computing

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A-59. Use a floppy disk and the diskcopy procedure. A-60. Magnetic tape.