THE DIFFERENT STYLES OF PERSONAL COMPUTERS

The world of personal computers is one of Apples, Lisa’s, Macintosh's, Compaq’s, Commodores, Eagles, Data Generals, and half a hundred others. While they all function much the same, not all are suitable for the needs of business, industry, or government. For example, many computers found in homes may be fine for video games or for handling a basic budget, but they often lack the capabilities and memory needed to handle most business applications. In business and industry, the IBM Personal Computer (IBM PC) has emerged as the primary machine for desktop computing. The IBM PC, also known as the Model One, is that company’s first entry into the personal computer market. The Model One, shown in Figure 23 with a monochrome monitor, has two disk drives, which means that it offers no internal long-term storage and is dependent on diskettes for its instructions and for storing work. The disk drives are the two open slots on the front of the microprocessor as pictured in Figure 23. The diskette containing the software program is placed in the left-hand drive and the diskette on which the work will be stored is put in the drive on the right. The system identifies the disk drives as:

FIGURE 23. Dual disk drive system. Courtesy of International Business Machines.

Drive A (the disk drive on the left)

Drive B (the disk drive on the right)

When the machine is turned off, it loses everything that was stored on it

The IBM XT, pictured in Figure 24 with a color monitor, has a hard disk installed, which makes internal long—term storage possible. This machine has one disk drive unit and a hard fixed disk. Diskettes containing the software or data to be worked on are loaded through the disk drive and then copied to the hard disk, which generally has a storage capacity of 10 megabytes.

The system identifies each of these units as:

Drive A (the disk drive on the left)

Drive C (the hard fixed disk)

A fixed disk drive makes it easier to switch from one program to another. It is also easier to integrate information from various

 

FIGURE 24. IBM hard disk system. Courtesy of International Business Machines.

Programs and files into a single document. An example would be to merge sections from an electronic spreadsheet program into a report being prepared under a word processing program. Un- like the PC, the XT will retain anything stored on its hard disk whenever the power is turned off. While each system can be equipped with up to 640K of short- term memory (RAM), there are some differences in the mother boards, which contain the main circuitry for a personal computer. The XT has the ability to add or expand the system by five additional devices or functions over what the PC can handle. Hard disks also operate faster than diskette drives. This allows access to more information at greater speeds. Another version of the PC is the AT, which can process information two or three times faster than an XT and has a fixed disk storage capacity of 20 megabytes. Figure 25 is a 3270 personal computer. Essentially, this is an XT that has been modified to also act as if it were a terminal connected to a mainframe. While this capability can exist in any personal computer in which an emulation board has been installed, a 3270 has everything built right in.

FIGURE 25. IBM 3270 Personal Computer. Courtesy of International Business Machines.

The 3270 personal computer also has a feature called windowing, which allows the display screen to be divided into as many as seven separate work areas. An analogy would be putting a report together from different piles of information. Instead of stacking everything on a desk, the computer can display data from up to four different sources simultaneously. There are also windows on which notes or reminders can be written and displayed. Portable computers such as the Compaq and Data General/One Laptop (see Figure 26) are also popular. These machines are often equipped the same way a desktop system is, and can perform identical functions and run the same software programs. Portable computers are totally self-contained and come with built- in monitors, disk drives, and, on some models, fixed disks (see Figure 27).

 

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Modems

Modems allow long-distance communication to take place between two computers by way of telephone lines or signals. Modems for personal computers may be one of two kinds: an internal modem (installed within the computer itself), or an external (a piece of hardware that connects to the computer). In addition to a modem, an active telephone outlet and a communications software package are needed.

Modems are used to produce signals compatible with telephone equipment. The equipment used in the telephone system requires that digital signals from a computer be converted to analog signals for transmission. Without a modem, telephone system amplifiers and filters would alter the digital signals and turn them into gibberish before they reach any other computer. Modems are grouped according to speed, features, and by their abilities to store dialing directories and make direct dial calls. Once equipped with a modem and the appropriate software, personal computers can dial any other system equipped to receive their calls; anywhere in the world. The various services that can be accessed include:

Up-to-the-minute stock prices

Movie reviews

Airline schedules and reservation services

Hotel and car rental reservation services

Public service bulletin boards, containing everything from free

Software to consumer tips and want ads

Shop-at-home service

Some of these services require the payment of a subscription fee, while others charge only the cost of the telephone call.

 

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COMMUNICATING WITH A MAINFRAME

Personal computers first found their way into most organizations for uses that generally required little additional information beyond what was readily available. People were quick to realize, however, that the real power in computing came from having access to the large volumes of information that were found on mini or mainframe systems. This information wasn’t available to personal computers because of their inability to exchange files with, or access software from, these larger computers. To get around this, terminal emulators were developed to allow a personal computer to act as if it were a part of the terminal network for a larger system. An emulator (sometimes called an emulation, or Irma, board) essentially fools the computer into thinking it is dealing with another dedicated terminal. A dedicated terminal is one that can be used only to put information into and take information out of a mainframe or minicomputer (the host). A dedicated terminal has no computing power of its own, and cannot process information it receives from the host. This is what makes personal computers so valuable and data processing departments so nervous. Personal computers equipped with emulators can access the main storage banks on the larger systems and then download, or remove information, from the host and place it in the personal computer’s memory, so that computing can actually take place on a worker’s desk. This essentially sidesteps data processing altogether under some circumstances. When the worker has finished whatever manipulation of the data is needed, it can be returned to the host through a process known as uploading. In order to accomplish these tasks, personal computers need to have: An emulation board installed Cabling, or another form of connection, such as a telephone line to the host Software, to make it work it is estimated by some data processing professionals that by 1990 as many as 25 percent of all mainframes installed in large companies in the United States will have personal computer-to- mainframe communications.

 

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Networking

Up to this point, most of the information in this book has been written from the standpoint of the personal computer as a standalone machine. One power of computing, however, is in linking several computers into what is called a local area network (LAN).

Personal computers can be linked directly to one another through a terminal network connected to a mainframe computer, or though smaller minicomputers that link personal computers within specific offices or departments. These minicomputers, in turn, might be tied into a larger mainframe (or host) computer. Generally, all connections are made either by direct cabling or through existing telephone lines.

In order to allow personal computers to communicate with one another, three things are needed:

1. A communications card, which is plugged into a computer to connect it to the network

2. Cabling and some control machinery to keep everything functioning in harmony

3. Software

The software is perhaps the most important ingredient, because it will have the biggest effect on the results a network is able to achieve.

Networks are valuable because they allow people to share information almost instantly. Let us say that a worker has a memorandum or some budget files that he or she would like to share with someone else on another floor. Using the network concept, 11w information could be put together on one personal computer and then sent directly to the second system. In many networks, the sender may even direct something straight to the recipient’s printer to produce a paper copy. It is important for those who plan to use a LAN to first decide what they want the network to do. Options range from sharing files easily and allowing many people to access them, to simple communications such as electronic mail. Other considerations include deciding what should be sent (voice, video, and data communications are all possible), and determining whether or not every personal computer in the network needs such capabilities. These considerations are what make the software so important, because programs differ substantially in terms of the services they can deliver.

 

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OUTPUT: PRINTERS, NETWORKING,AND TRANSFERRING DATA

Printers

A number of things can happen to information after a user has finished working with it. In some cases, it may be enough to just see it on a monitor, or send it to a storage device. In most situations, however, it will probably be shared with other people.

The most common means of sharing computer information is to make a printed copy of it. While there are many brands of printers available in the marketplace, three kinds are generally available for personal computers: dot-matrix, letter quality, and nonimpact. The following comparison of these three kinds of printers originally appeared in Microcomputers for Insurance Professionals, written by Kenneth and Christina McClung, and John Guarneri

Dot-Matrix Printers

The dot-matrix printer gets its name from the way it produces characters. The print head has a set of wires that produce tiny dots according to a specific matrix pattern. For instance, an 8 x 9 dot- matrix printer produces dots in a matrix 8 dots wide by 9 dots high. The positioning of the dots determines the character formed. This method of printing is quick and inexpensive, but the quality of the characters produced is not as good as that of a letter-quality printer. (See Figure 22.)

A rule of thumb regarding dot-matrix printers is that the greater the number of dots in the matrix, the higher the quality of printed output: For example, a 9 x 23 matrix will produce higher quality print than will an 8 x 9 matrix. Some dot-matrix printers can approach letter quality by overprinting each character a second time with a light offset. This increase in the quality of appearance must be weighed against the reduction in output speed incurred by having each character printed twice.

  Figure 22. Dot matrix printer. Courtesy of International Business Machines.

The Letter-Quality Printer

The letter-quality printer produces the same high quality, fully formed characters as a typewriter. These printers give your correspondence a more professional appearance. In addition you can change the type style of your output with most letter-quality, printers. Letter-quality printers usually use removable typing elements available in most popular type styles. Depending on the brand of printer, this element may take the shape of a daisy wheel, a thimble, or the familiar IBM-style ball. (See Exhibit 6.)

Non impact Printers

Non impact printers are fast, quiet and generally the most expensive type of printers, with the cost often starting at $1,000. Some non impact printers also offer greater resolution and color graphics for users who need to produce sharp charts, reports and presentations. There are three kinds of non impact printers available: laser, ink-jet and thermal-transfer.

Laser: A laser printer uses a laser beam to write an image onto the photo conducting drum of a photocopier mechanism where the patterns pickup toner that is then transferred to a sheet of paper.

Ink-jet: Ink-jet printers spray ink at the paper at high speed, driving the ink into the surface with the impact.

Thermal-transfer: Thermal-transfer printers melt an image onto the paper by using precision heating elements and either a thermal ribbon or a transfer sheet.

 

 EXHIBIT 6. Comparison of text created by different types of printers. Reprinted with permission from Microcomputers for Insurance Professionals, McCluny, Guerriesi, and McCluny, John Wiley and Sons, 1984.

 

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