Floppy Disk Drives

FLOPPY DISK DRIVES CONTENT

1. Introduction 2. History 3. Parts of Floppy Disk 4. Writing Data on Floppy Disk 5. Floppy Disk Drive Facts 6. Types & Specification 7. Floppy Disk Formats

Floppy Disk Drive

8 inch, 5 ¼ inch, and 3.5 inch drives  Floppy Disk Drive 8 inch, 5 ¼ inch, and 3.5 inch drives  Date Invented:1969 (8 inch), 1976 (5 ¼ inch), 1983 (3.5 inch)  Invented By: IBM team led by David Noble  Connects to: Controller via cable INTRODUCTION The floppy disk drive (FDD) was the primary means of adding data to a computer until the CD-ROM Drive became popular. In fact, FDDs have been a key component of most personal computers for more than 20 years.  Basically, a floppy disk drive reads and writes data to a small, circular piece of metal-coated plastic similar to audio cassette tape. In this article.  Floppy disks are read and written by a floppy disk drive or FDD, the initials of which should not be confused with "fixed disk drive", 

which is another term for a hard disk drive. Invented by IBM, floppy disks in 8", 5.25", and 3.5" formats enjoyed many years as a popular form of data storage and exchange, from the middle 1970s to the late 1990s. HISTORY The floppy disk drive (FDD) was invented at IBM by Alan Shugart in 1967. The first floppy drives used an 8-inch disk (later called a "diskette" as it got smaller), which evolved into the 5.25-inch disk that was used on the first IBM Personal Computer in August 1981. The 5.25inch disk held 360 kilobytes compared to the 1.44 megabyte capacity of today's 3.5-inch diskette. The 5.25-inch disks were dubbed "floppy" because the diskette packaging was a very flexible plastic envelope, unlike the rigid case used to hold today's 3.5-inch diskettes. By the mid-1980s, the improved designs of the read/write heads, along with improvements in the magnetic recording media, led to the lessflexible, 3.5-inch, 1.44-megabyte (MB) capacity FDD in use today. For a few years, computers had both FDD sizes (3.5-inch and 5.25-inch). But by the mid-1990s, the 5.25-inch version had fallen out of popularity, partly because the diskette's recording surface could easily become contaminated by fingerprints through the open access area. Parts of a Floppy Disk Drive 1. The Disk  A floppy disk is a lot like a cassette tape  Both use a thin plastic base material coated with iron oxide. This oxide is a ferromagnetic material, meaning that if you expose it to a magnetic field it is permanently magnetized by the field.  Both can record information instantly.  Both can be erased and reused many times.  Both are very inexpensive and easy to use.  A floppy disk, like a cassette tape, is made from a thin piece of plastic coated with a magnetic material on both sides. However, it is shaped like a disk rather than a long thin ribbon. The tracks are arranged in concentric rings so that the software can jump from "file 1" to "file 19" without having to fast forward through files 2-18. The diskette spins like

a record and the heads move to the correct track, providing what is known as direct access storage. The Drive The major parts of a FDD include:  Read/Write Heads: Located on both sides of a diskette, they move together on the same assembly. The heads are not directly opposite each other in an effort to prevent interaction between write operations on each of the two media surfaces. The same head is used for reading and writing, while a second, wider head is used for erasing a track just prior to it being written. This allows the data to be written on a wider "clean slate," without interfering with the analog data on an adjacent track.  Drive Motor: A very small spindle motor engages the metal hub at the center of the diskette, spinning it at either 300 or 360 rotations per minute (RPM).  Stepper Motor: This motor makes a precise number of stepped revolutions to move the read/write head assembly to the proper track position. The read/write head assembly is fastened to the stepper motor shaft.  Mechanical Frame: A system of levers that opens the little protective window on the diskette to allow the read/write heads to touch the dual-sided diskette media. An external button allows the diskette to be ejected, at which point the spring-loaded protective window on the diskette closes.  Circuit Board: Contains all of the electronics to handle the data read from or written to the diskette. It also controls the stepper-motor control circuits used to move the read/write heads to each track, as well as the movement of the read/write heads toward the diskette surface.

Writing Data on a Floppy Disk  The following is an overview of how a floppy disk drive writes data to a floppy disk. Reading data is very similar. Here's what happens:  The computer program passes an instruction to the computer hardware to write a data file on a floppy disk, which is very similar to a single platter in a hard disk drive except that it is spinning much slower, with far less capacity and slower access time.  The computer hardware and the floppy-disk-drive controller start the motor in the diskette drive to spin the floppy disk.  The disk has many concentric tracks on each side. Each track is divided into smaller segments called sectors, like slices of a pie.  A second motor, called a stepper motor, rotates a worm-gear shaft (a miniature version of the worm gear in a bench-top vise) in minute increments that match the spacing between tracks. The time it takes to get to the correct track is called "access time." This stepping action (partial revolutions) of the stepper motor moves the read/write heads like the jaws of a bench-top vise. The floppy-disk-drive electronics know how many steps the motor has to turn to move the read/write heads to the correct track.  The read/write heads stop at the track. The read head checks the prewritten address on the formatted diskette to be sure it is using the correct side of the diskette and is at the proper track. This operation is very similar to the way a record player automatically goes to a certain groove on a vinyl record.  Before the data from the program is written to the diskette, an erase coil (on the same read/write head assembly) is energized to "clear" a wide, "clean slate" sector prior to writing the sector data with the write head. The erased sector is wider than the written sector -- this way, no signals from sectors in adjacent tracks will interfere with the sector in the track being written.  The energized write head puts data on the diskette by magnetizing minute, iron, bar-magnet particles embedded in the diskette surface, very similar to the technology used in the mag stripe on the back of a credit card. The magnetized particles have their north and south poles oriented in such a way that their pattern may be detected and read on a subsequent read operation.  The diskette stops spinning. The floppy disk drive waits for the next command.

 On a typical floppy disk drive, the small indicator light stays on during all of the above operations. Floppy Disk Drive Facts  Two floppy disks do not get corrupted if they are stored together, due to the low level of magnetism in each one.  In your PC, there is a twist in the FDD data-ribbon cable -- this twist tells the computer whether the drive is an A-drive or a B-drive.  Like many household appliances, there are really no serviceable parts in today's FDDs. This is because the cost of a new drive is considerably less than the hourly rate typically charged to disassemble and repair a drive.  If you wish to redisplay the data on a diskette drive after changing a diskette, you can simply tap the F5 key (in most Windows applications).  In the corner of every 3.5-inch diskette, there is a small slider. If you uncover the hole by moving the slider, you have protected the data on the diskette from being written over or erased.  Floppy disks, while rarely used to distribute software (as in the past), are still used in these applications: – in some Sony digital cameras. – for software recovery after a system crash or a virus attack – when data from one computer is needed on a second computer and the two computers are not networked – in bootable diskettes used for updating the BIOS on a personal computer – in high-density form, used in the popular Zip drive Summary of Floppy Disk Types and Specifications The following table shows a summary of the various floppy disk specifications provided in other sections of this chapter, for each of the five major floppy disk types: Category

Specification

360 KB 5.25"

1.2 MB 5.25"

720 KB 1.44 MB 3.5" 3.5"

2.88 MB 3.5"

Drive

Controller

Media

Geometry

File System

Read/Write Heads (Data Surfaces)

2

2

2

Spindle Motor Speed

300 RPM

360 RPM

300 RPM

Minimum Controller Transfer Rate

250 Kbits/s

500 Kbits/s

250 Kbits/s

500 Kbits/s

1 Mbits/s

Track Density (TPI)

48

96

135

135

135

Bit Density (BPI)

5,876

9,869

8,717

17,434

34,868

Density Name

Double Density (DD)

High Density (HD)

Double Density (DD)

High Density (HD)

ExtraHigh Density (ED)

Tracks (Cylinders)

40

80

80

80

80

Sectors Per Track/Cylinder

9

15

9

18

36

Total Sectors Per Disk

720

2,400

1,440

2,880

5,760

Cluster Size

2 sectors

1 sector

2 sectors

1 sector

2 sectors

Maximum Root Directory Entries

112

224

112

224

448

2

2

300 RPM 300 RPM

Unformatted Capacity

~480 KB

Formatted Capacity (binary kilobytes)

360

Formatted Capacity (bytes) Capacity

File System Overhead (bytes) Total Usable Capacity (bytes)

~ 1.6 MB ~1 MB

1,200

720

~2 MB

~4 MB

1,440

2,880

368,640 1,228,800 737,280 1,474,560 2,949,120

6,144

14,848

7,168

16,896

17,408

362,496 1,213,952 730,112 1,457,664 2,931,712

Total Usable Capacity (binary KB)

354

1,185.5

713

1,423.5

2,863

Total Usable Capacity (binary MB)

0.346

1.158

0.696

1.390

2.796

Floppy Disk Formats and Logical Structures There are several different disk formats that are in common use on the PC platform. Actually, "common use" is debatable, because really only one format is used any more, and even it has limited uses these days. This section takes a look at the different floppy disk formats used for the various types of drives. It also looks at how the FAT file system is implemented on floppy disks. 360 KB 5.25" Floppy

The oldest floppy disk format is the 360 KB 5.25" floppy disk. This is the type of disk that was used in the very first IBM PCs, which in fact didn't use a hard disk at all. The 360 KB floppy is the only format that uses 40 tracks per side to record data; the others all use 80 tracks. This accounts for its low capacity. Older versions of these drives were full-height models; the halfheight models were introduced later. 1.2 MB 5.25" Floppy The high density 1.2 MB floppy disk debuted in the IBM AT in 1984, as a standard feature (the 360 KB floppy was optional). The increase in capacity of this disk, over 200% compared with the 360 KB version, all but obsoleted the smaller format rather quickly. The 1.2 MB floppy disk can still read and write 360 KB floppies, but problems can occasionally result. Since the floppy uses a higher bit density, the 1.2 MB floppy requires a floppy disk controller capable of 500 kbits/s data transfer Virtually all newer controllers support this rate. 720 KB 3.5" Floppy The original version of the 3.5" floppy disk held 720 KB of data and was introduced in 1986. This version of the 3.5" never became very popular both because it offered 40% less capacity than the 1.2 MB 5.25" drive, and because it was so quickly replaced by the high density 3.5" disks. 1.44 MB 3.5" Floppy The only floppy disk format still in wide use, the 1.44 MB 3.5" drive was introduced by IBM in 1987 as part of its PS/2 line. Since that time they have grown immensely popular, and this format is the standard for floppy disks today. Virtually every PC made since 1987 uses one of these drives, and there are many non-PC computers that will read them as well. They have become very cheap due to the aging of the technology and the fact that they are produced in such high volume. Their universality is what has allowed the floppy to continue to be a default part of every PC despite their rather tiny storage capacity compared to today's hard disks. Since the 1.44 MB uses a higher bit density than the 720 KB, it requires a floppy disk controller capable of 500 kbits/s data transfer. Virtually all newer controllers support this rate.