Records and files OF Programs

Computers store and process information in records and flies (see Figure 19). A record is a collection of related items that are stored in memory. A file is a collection of related records that are treated as a single unit. For example, you have sent a group of letters to a company called Jim’s Shoes and PC Emporium. Within the computer, the file becomes “Jim’s Shoes.” Each letter sent (and stored) represents one record of that file, as can be seen in Figure 20.

When you create a file, you may tall it almost anything you like, as long as it does not exceed eight characters in length. There

 

FIGURE 19. Computers manage data much the same as you handle files. Drawing courtesy of International Business Machines.

FIGURE 20. Drawing by Gina Bean.

are, however, certain characters that cannot be used in file names because the operating system reserves them to refer to system components. These include:

CON

AUX

COMI

LPT1

PRN

NUL

A complete list of all file names in either the program you are using, or the files you create, are available in a directory. A directory shows the file name, how much space (in bytes) it takes up. And the date it was created. Diskettes are capable of holding up 1e 112 files each.

When setting tip a file, try to make the file name as descriptive of a file's contents as the eight character limitation will allow (see Figiure28).

EXAMPLES OF FILE NAMES

Good                                                                                           Bad

Inventory                                                     Inventory (has more than eight characters)

Table                                                             (contains a space that isn’t allowed)

 

FIGURE 21. Courtesy of International Business Machines.

File name extensions

A file name extension is a brief three-character addition to a file name used to help identify or categorize the type of file it is. Extensions appear after the file name and are separated from them by a (.). One example might be book.fic, which would identify a series of sub files within the main file. In this case, the primary file identifies books, and the file name extension further breaks that down to works of fiction.

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TYPES OF MEMORY STORED WITHIN A SYSTEM

There are two types of memory stored within a system:

1. Read Only Memory (ROM)

2. Random Access Memory (RAM)

Read Only Memory is permanently imprinted in your computer when you get it. It is called ROM because it is meant to be read only by the computer itself. The person operating the computer has no control over it. The computer uses this memory to tell itself how to start up when you turn it on. Read Only Memory processes the electrical data flow from the keyboard to the CPU and from the CPU to the video display screen or to any other peripheral equipment you have attached, such as a printer. The decoders that translate numbers and characters into binary information that the computer understands are found in ROM. These programs are called firmware, or nonvolatile, because they are always there, and are not erased or destroyed when the power is turned off.

The other memory a system works with is called, Random Access Memory (RAM). This is what some people also call Read/ Write Memory, and is considered volatile because the information stored here is lost whenever the computer is shut off, or when power is lost. Random Access Memory is controlled by the person working with a system, and is where the instructions and information needed to get a job done are temporarily stored. Personal computer systems are often described by the amount of short- term (RAM) memory available (i.e., 64K, 256K, 640K). Most software programs also list the amount of memory they require to be stored in RAM. Most systems allow the user to increase the amount of memory available by installing additional single memory chips or expansion boards containing multiple chips. Even with these, however, there are finite limits to the amount of memory a personal computer has to work with. This is one reason why it is important to decide what kinds of work you would like to perform on a personal computer and the software most appropriate for accomplishing those tasks, before you purchase the system. This allows a computer to be configured to meet anticipated uses and eliminates the problem that a lot of people encounter of trying to install a software program that requires more memory than their system has available. In these situations the only recourse is to purchase and install more memory. A person using a computer comes in contact with all of its working parts. When a system is first turned on, the operating system takes over and makes sure everything under its control is functioning properly. Information is put into the system, where it is stored in memory according to an address code assigned by the computer, as seen in Figure 14. When the program (or list of instructions) is loaded, data are taken from the memory. Following the program instructions, the

FIGURE 14.  The flow of information processing. Illustration by Gina Bean. Data are then worked on in the Arithmetic Logic Unit (ALU). When all the instructions have been carried out, the information is returned to memory or to an output device.

Output can be delivered through any of several sources:

.Video Monitor (CRT)

.Printer

.Voice synthesizer

.Modem for transferring information over telephone lines

.Storage device (diskette, hard disk, etc.)

 

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HOW A COMPUTER OPERATES

What goes on inside a computer is a mystery to most people, and even a little frightening to some. Actually, it is a fairly simple process - Whether we are talking about a supercomputer or one that can sit on top of a desk, all function in the same general way.

To understand how computers operate, we first have to break them down into several basic elements:

1. Input

2. Central processing unit (CPU)

3. Memory or storage

4. Output

Information is put into the computer through any of several different sources:

1. Keyboard

2. Data diskette (which can contain the program of instructions

What Are The Components Of A Personal Computer

The hardware components (those things you can see and touch), for a personal computer include:

A microprocessor (or system unit)—This is the Central Processing Unit (CPU) for a personal computer. While it looks like a box, it contains the memory systems (RAM and ROM) and is really the heart of the system. This unit also contains the disk drives. Since the memory is wiped clean each time you turn the machine off, you need a more permanent storage system. This is provided by keeping separate memory diskettes.

• A keyboard that lets you communicate with the system.

• A video display monitor (like a TV screen) that lets the system communicate with you.

• A printer that can produce a paper copy of whatever you are working on.

Diskettes—The software containing the programs you wish to run or on which to plan your work. A diskette is a small magnetic record that contains the storage space for your memory. When a diskette is inserted into a disk drive, it is spun much like a record on a turntable, and “read” electronically. A single sided diskette can hold the same amount of information as 110 pages of single-spaced text.

You will be working with, or the information you will be working on)

1. Cassette tape

2. Graphic tablets and electronic pens

3. Light pens, which can be used by directly touching the screen of a monitor

One key point to remember is that a computer will do exactly as it is told, and only what it is told. This can lead to what programmers call GIGO or Garbage In, Garbage Out. If the user doesn’t give the computer the correct information to work with, and precise’ instructions on what to do with that information, he or she will get back incorrect or meaningless answers and results.

Data is entered into the CPU. The CPU is where all the logical and control functions of a computer are carried out. The CPU is actually divided into two areas: a control unit, and the arithmetic and logic unit (ALU). The control unit spends its time figuring out what the computer is supposed to do next, and the ALU actually does it.

Memory is where information and instructions are stored. How does a computer memorize? A series of on/off switches lead an electrical current to a particular location, or address. Information is moved between the CPU and its memory banks by electronic pathways or conduits, called registers.

 

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Supercomputers

Specially designed systems (usually several computers tied together). Used primarily in government or research. These are the most expensive and largest systems available, and they possess tremendous computing power. The cost of operating and maintaining them makes them prohibitive hit most organizations. One example of a supercomputer Is 11w one operated by the National Security Agency. Built at a cost 

 
 FIGURE 9. Cray Supercomputer shown here with designer Seymour Cray of Cray Research, Inc.

Of approximately $15 million, it is rumored to be capable of 150 to 200 million calculations per second, and has a memory capable of transferring  320 million words per second. This system is reported to be so powerful that the heat is generates would melt is down were it not for a specially designed cooling system.*

At present, there are some 150 supercomputers (similar to that in Figure 9), in operation around the world, with most located in the United States. The latest models have a memory capacity  some two billion bytes and processing speeds 40,000 to 50,000 times faster than a personal computer. Tasks that once took a year to accomplish on a second-generation computer can be done in about a second with a supercomputer.* Mainframes. These are the large machines that come to mind when most people think of computers. Costing hundreds of thousands of dollars, and requiring specially built facilities and large supporting staffs of operators, programmers, and analysts, they are designed to handle large volumes of work or complex calculations.

Minicomputer. Smaller than a mainframe and generally costing under $200,000, these systems are ideally suited for a medium- sized organization. They require smaller facilities and less staff than the mainframes, but have enough, power to process a wide range of commercial or scientific jobs.

Microcomputer. This is where the personal computer fits in. Designed to sit on the top of a desk, and within the financial reach of most organizations and many individuals, these systems represent the latest evolutionary stage. While not yet in the same league as their larger cousins, they can easily match or outperform the computing power of their first- and second- generation ancestors.

Lap-Top Computers. An offshoot of the personal computer, these small systems (many are complete with printer and liquid crystal displays) can offer the same type of power and functionality as a desktop model. Designed for portability, they can travel inside an attach case as seen in Figure 10, and can be used just about anywhere.

While personal computers can trace their lineage back several centuries (see Exhibit 5), they are a relatively new phenomenon. The personal computer revolution really got underway in 1969 with the invention of the Intel 4004 microprocessor, which contained 2250 transistors on a single microchip. At first, these were available only to large manufacturers, but in 1971 Intel decided to clear out its stocks by offering the 4004 microprocessor for

*Philip Elmer-Dewitt, “A Sleek, Super powered Machine,” Time (June 17, 1985). 53.

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Fear oF Damaging The Computer

When they first begin working with a personal computer, many people hardly touched the keyboard for fear of doing something that would cause damage to the computer. People who don’t think twice about slamming down a telephone receiver, or driving their car to its very limits, suddenly grow passive when confronted with a keyboard. From secretaries to corporate executives to the folks down on the loading dock, there is something about a computer keyboard that can turn each into a shrinking violet.
There are two basic reasons for this initial passivity
1. The perception that despite their power, computers are extremely fragile devices.
2. The feeling that computers are on a somewhat different plane than other types of tools, the "gift of the God" syndrome.
Let's take a closer look at each of these observations. The first is a result of the day-to-day contacts that most people have with computers and the limited knowledge they possess about them. From the average person’s vantage point, computers are like newborn infants that need special handling and protection. Most people never see the large mainframe systems where they work. These computers are typically locked away behind security doors, in guarded environments with their own air conditioning, heating, electrical, and humidity control systems. From the outside looking in, it would appear that computers require a lot of care and attention. This particular point of view is often strengthened by day-today experiences that may often be punctuated by periods when the computer isn’t available. In the jargon of data processing, people are told of down time, system failure, or crashes, without any idea what those things might really relate to. Small wonder that when they suddenly come face to face with a personal computer some people are somewhat reluctant to touch it. After all, if the big ones come tumbling down from time to time, despite the care and attention of experts, what will happen when they start touching one? The second observation is that some people view computers in a somewhat different light than they do other office tools, maybe because of the sheltered environment that most people associate with the large systems. Computers operate in an almost mystical realm. Movies and popular works of fiction have pictured them as extending human powers beyond those of the body and mind. We think computers can solve complex problems almost in the blink of an eye. What could take a human hours, days, years, or even decades to work through might be processed in a matter of seconds or minutes by a computer. A mystique has grown up around not only the systems themselves, but also around the people who work with them. In a society that is growing increasingly dependent on technology, many who lack education or insight into computers look on those who can make them work in much the same way that ancient cultures viewed their high priests. As computers have become increasingly insulated, their operations cloaked in jargon and acronyms foreign to most people, many ascribe a certain reverence and awe to everything associated with them. Computers, and those who run them, have come to occupy a special niche beyond the province of the average person. With the arrival of the personal computer, all this is suddenly changing. Now individual workers are being given access to the same power and magic previously associated with the large systems. For some, this sharing of the technology can be likened to the Greek gods descending from the mountain top to share their secrets with their mortal followers. Against these backgrounds, it’s easy to understand why many men and women are apprehensive when it comes to touching a personal computer for the first time. As computers are extended through organizations, it is important for people to see them in the same light as they do other fixtures of the office, such as telephones and copiers. Some of this will certainly occur over time and with increased usage, and can be facilitated through introductory training programs that emphasize or demonstrate the difficulty actually damaging a system. The message that should come across is that while a lot of things. Can occur to the information they are working with, simply banging away on the keyboard won’t do much to actually harm the computer itself.

 

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