FLOPPY DISK DRIVE OPERATION

THE 3.5-INCH FLOPPY DISK CONSTRUCTION Figure 10-6 shows a 3.5-inch disk. The 3.5-inch and 5.25-inch disks are constructed of the same basic materials. The disk is a thin flexible polyester film base that is coated with a magnetic compound. This compound is iron-oxide for standard and double- density disks and a cobalt ferric compound for high- density disks. Disk Case The 3.5-inch floppy disk’s rigid plastic case stabilizes the disk as it spins. This allows for greater densities of data to be written on the disk. Media Access Hole and Shutter Examining the case of a 3.5-inch disk, you’ll notice several differences from the 5.25-inch disk. The first difference is the metal shutter covering the media access hole. This shutter is spring loaded and moves out of the way to expose the disk when the disk is loaded into a drive. When the disk is not loaded in a drive, this shutter covers the hole and eliminates the need for a disk jacket to store the disk. Write Protect/Write Enable Slide Write protection for the disk is accomplished by means of a slide switch in the lower left comer of the disk. Figure 10-6 illustrates the location of the write protect/write enable slide switch. When the slide switch is positioned so you can see a hole through the case, the disk cannot be written on. Media Indicator Hole On the lower right corner of some 3.5-inch disks is another hole that designates the disk as a high-density disk. When a high-density disk is loaded into a high-density drive, a sensor checks for the presence of this hole. If it is present, the disk can be formatted in the 1.44M mode. If this hole is not present, the disk can only be formatted as a 720K disk. FLOPPY DISK DRIVE OPERATION Several basic components are common to all floppy disk drives. To properly test, install, or service a disk drive, you must be able to identify these components and understand their functions in the drive. Figure 10-7 shows a typical 5.25-inch disk drive with the major components labeled as follows: Spindle assembly/drive motor Drive electronics circuit board Connectors Head actuator assembly Read/write head arm assembly Spindle Assembly/Drive Motor Figure 10-6.—The 3.5-inch floppy disk. The spindle holds the disk in place while it spins. The drive motor spins the spindle at the proper speed. Most floppy disk drive motors spin at 300 rpm except the 1.2M drive, which spins at 360 rpm. Almost all half-height drives use a direct drive motor to turn the spindle, and the speed cannot be adjusted. Some older Ml-height drives use a belt-driven motor. These belt-driven drives usually have a strobo-disk mounted on the underside of the drive set to both 50 Hz and 60 Hz. To adjust the speed, you remove the drive and issue a command to get the motor running. Look at the strobo-disk under a fluorescent light and adjust the drive speed until the outer strobo-disk spokes appear to be standing still. The inner disk is setup for 50 Hz operation, the frequency of European main power. 10-8