KEY CONCEPTS access time How long it takes to retrieve data from a drive. Access time is made up of seek time (how long it takes for a read/write head to position itself over a particular track), settle time (the time it takes the head to stabilize), and latency (how long it takes for the required sector to rotate until it’s under the head). All are measured in milliseconds. duster
One
or more successive sectors
that
contain a contiguous group of data. It is the smallest unit in which data is stored on a
drive. compression
A process
to remove redundant data so that a file is smaller. cookie The Mylar disk to which data is
written in a floppy drive. data transfer rate The number of bytes or megabytes transferred from a drive to memory (or from any storage device to another) in a second. Directory A set
of related files, also called a folder
in Windows 95
and 98. The files may be located physically
on different parts of a drive, but they are grouped logically in a directory,
which can contain other folders or subdirectories. drive array Two or more drives linked to improve file retrieval time and provide error correction. Iormat The process by which a disk is divided into tracks and sectors so that files can be stored and found in an orderly fashion. fragmentation The process by which files become broken up into widely separated clusters. Defragging or optimization corrects fragmentation by rewriting broken files to contiguous sectors. write head The drive component that writes data to a drive and reads it by using magnetism or laser. Super fast, super big hard drives, magneto-optical drives, CD-ROM drives, DVD drives, and all the other new high-tech marvels, it’s hard to get excited about the common floppy drive. After all, it’s slow and a floppy disk doesn’t store much information compared to... well, compared to any other type of disk. When the size of software is measured in tens of gigabytes, it’s the rare program these days that’s still distributed on floppy instead of a CD. But for all its deficiencies, the floppy drive is an under appreciated wonder. Think of it: An entire book full of information can be contained on a disk that you can slip into your pocket. Floppy drives are ubiquitous, making them a sure and convenient way to get data from one PC to another. No communication lines, networks, gateways, or infrared links are needed; just pull the floppy out of one machine and slip it into another. But given the gargantuan size of Windows and its applications, most programs are now distributed on CD-ROM. And the floppy is challenged by overachieving cousins, such as the ZIP drive. Still, for all its commoner heritage, the floppy is cheap and dependable and respectable. It will be with us in some form for a long time to come.
Although smaller, faster, and more capacious floppy drives are now standard components of all new computers, it took years for them to supplant the old 5.25-inch floppy drive. That early drive was the 78-rpm phonograph record of the computer world. Long after smaller records that played more music with greater fidelity were available, phonograph companies continued to produce turntables with 78-rpm settings just because many music lovers had so much invested in 78s. When the first edition of this book was published in 1993, it was common for PCs to be sold with both the 5.25-inch and newer 3.5-inch drives. Today, a 5.25-inch drive is an artifact of forgotten, primitive times. With capacities today ranging from 700 kilobytes to 2.88 megabytes, 3.5-inch disks hold more data than their older cousins. Their protective cases mean that we can be downright careless about how we handle them, and they are so cheap that their cost is not a factor. And they are so entrenched that it will be years before they’re supplanted by the writeable compact discs and DVDs at are just emerging. When you push a 3.5-inch floppy disk into the drive, the floppy presses against a system of levers. One lever opens the floppy’s shutter to expose the cookie-a thin Mylar disk coated on either side with a magnetic material similar to the coating on a cassette tape that can record data. When the heads are in the correct position, electrical impulses create a magnetic field in one of the heads to record data to either the top or bottom surface of the disk. When the heads are reading data, they react to magnetic fields generated by the metallic particles on the disk by sending electrical signals to the computer. A stepper motor—which can turn a specific distance in either direction according to signals from the circuit board—moves a second shaft that has a spiral groove cut into it. An arm attached to the read/write heads rests inside the shaft’s groove. As the shaft turns, the arm moves back and forth, positioning the read/write heads over the disk.
|
