Figure 1-18.—Floppy disks/diskettes used on microcomputers

(3.50) inches (see figure 1-18). The platter is made of a tough plastic that is coated with a magnetic oxide material, allowing it to be magnetized. The inside of the plastic jacket is lined with a soft wiping material that continuously cleans the floppy disk as it spins within the jacket. Look at figure 1-19; you will notice a hole in the middle of the diskette. It is referred to as the center hub. The hub makes it possible for the floppy disk drive’s spindle to rotate the diskette inside the jacket. The recording window allows the read-write head mechanism of the floppy disk drive to come into contact with the diskette so it can read from or write data onto the diskette’s surface. Located just to the right of the center hub is what we refer to as an index hole. This index hole (and corresponding hole [or holes] in the diskette), marks the first sector or starting point on the diskette. The sectors on a diskette are controlled by timing. On a soft-sectored diskette, the timing is controlled by the software; therefore, only one timing hole is needed on the diskette. On a hard-sectored diskette, the timing is controlled by the hardware, and the diskette has several timing holes. Types of Floppies/Diskettes.— The diskettes you will be using must be compatible with the floppy disk drives on your microcomputer system. Diskettes can be soft-sectored or hard- sectored. Depending upon the disk drive’s characteristics, the disk drive can record data on one side of the diskette or both and can record data in one of several bit densities, depending upon how the diskette is formatted. When you are working with a soft-sectored diskette, you must use your microcomputer and a utility routine or program (in this case, a formatter program) to sector or format each diskette for you. On most microcomputer systems, using the F O R M AT command will automatically sector the diskette for you. If you are working with hard-sectored diskettes, then you need not format them. They have already been presectored by the manufacturer for your specific Figure 1-18.—Floppy disks/diskettes used on microcomputers. Figure 1-19.—A typical 5.25-inch diskette. microcomputer system. Floppy disk drives that use hard-sectored diskettes read and write data faster. However, the diskettes are more expensive and can only be presectored (reformatted) for a specific system, such as an IBM compatible or a Macintosh. Most diskettes sold today are soil-sectored because the wide range of microcomputers and their operating systems vary considerably in respect to sectoring re- quirements. For now, the important thing to remember about sectoring is the fact that no matter what type of diskette you are working with (soft- or hard- sectored), it must be formatted before it is usable for storing data. Storage Capacity.— Although diskettes are relatively small in size, they can store a respectable amount of data. Some diskettes are single-sided, single-density, whereas others are double-sided, single-density; double-sided, double-density; or double-sided, quad-density. When we refer to a diskette as being double-sided, double-density, what are we really saying? We are saying the floppy disk drive is able to read from and write to both sides of the diskette (hence, the term double-sided), and that each sector on the disk can store 512 bytes of information (instead of the 256 bytes that can be stored on a single-density diskette); hence, the term double-density. A diskette’s capacity is also affected by the number of tracks per side. Therefore, if you wanted to know the total storage capacity of a double-sided, double-density diskette with 80 fifteen- sector tracks per side, then you would use the following formula to calculate the number of bytes: 1-19