keyboard, a computer, two floppy disk drives (A & B), and a printer. Look at the example in figure 1-12.">
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.
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.
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:
This means the computer is not reading anything in A drive. Check for:
Another error message you might receive at this time is:
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:
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.
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>).
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.
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.
Figure 1-13. - Floppy disk.
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.
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.
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.
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.
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?