Scott Muellers Upgrading and Repairing Laptops, Second Edition
Floppy Drives
Although no longer used for primary storage, the floppy is still a useful accessory as a system-installation and configuration device, especially for troubleshooting. When you're installing an operating system from scratch, the floppy is often used to load the software necessary for partitioning and formatting the hard disk, as well as to run diagnostics in case of problems. Starting in 2002, many companies started selling systems without floppy drives. This started with laptop computers, where internal floppy drives were first eliminated and replaced with external (normally USB) drives. Most newer laptops no longer include a floppy drive with the system, offering only external USB models as an option. In 2003, many desktop system manufacturers likewise stopped including a floppy drive in their standard system configurations. Even though higher-capacity storage devices are available and most modern systems can boot directly from CD-ROMs, the ubiquitous floppy drive will likely remain a useful option or accessory in systems for at least another few years . Both Zip and SuperDisk drives have failed in the marketplace as floppy drive replacements , but a new standard called Mount Rainier (also known as EasyWrite) will finally allow CD-RW and DVD+RW drives to serve as a replacement for the floppy. Prior to Mount Rainier, optical drives lacked defect management as well as native OS support. Alan Shugart is generally credited with inventing the floppy disk drive in 1967 while working for IBM. One of Shugart's senior engineers , David Noble, actually proposed the flexible medium (then 8 inches in diameter) and the protective jacket with the fabric lining . Shugart left IBM in 1969, and in 1976 his company, Shugart Associates, introduced the minifloppy (5 1/4-inch) disk drive. It, of course, became the standard eventually used by personal computers, rapidly replacing the 8-inch drives. He also helped create the Shugart Associates System Interface (SASI), which was later renamed SCSI (Small Computer System Interface) when approved as an ANSI standard. Sony introduced the first 3 1/2-inch microfloppy drives and disks in 1983. The first significant company to adopt the 3 1/2-inch floppy for general use was Hewlett-Packard in 1984 with its partially PC-compatible HP-150 system. The industry adoption of the 3 1/2-inch drive was furthered when Apple used it in the first Macintosh systems in 1984, and IBM put the drive into its entire PC product line starting in 1986. Drive Components
All floppy disk drives, regardless of type, consist of several basic common components. Note that all floppy disk drives are still based on (and mostly compatible with) the original Shugart designs, including the electrical and command interfaces. Compared to other parts of the PC, the floppy disk drive has undergone relatively few changes over the years (see Figure 10.20). Figure 10.20. A typical floppy disk drive.
A floppy disk drive has two read/write heads ”one for each side of the disk, with both heads being used for reading and writing on their respective disk sides. A motor called a head actuator moves the head mechanism. The heads can move in and out over the surface of the disk in a straight line to position themselves over various tracks. On a floppy drive, the heads move in and out tangentially to the tracks they record on the disk. This is different from hard disks, where the heads move on a rotating arm similar to the tone-arm of a record player. Because the top and bottom heads are mounted on the same rack, or mechanism, they move in unison and can't move independently of each other. The upper and lower heads each define tracks on their respective sides of the disk medium, whereas at any given head position, the tracks under the top and bottom head simultaneously are called a cylinder . Most floppy disks are recorded with 80 tracks on each side (160 tracks total), which is 80 cylinders . Floppy Drive Interfaces
Floppy drives can be interfaced to a system in several ways. Most use the traditional floppy controller interface, but many now use the USB interface. Because the traditional floppy controller only works internally, all external drives are interfaced via USB or some other alternative interface. USB drives often have a standard floppy drive inside an external box with a USB-to-floppy controller interface converter inside. Newer systems that are "legacy free" don't include a traditional floppy controller and typically use USB as the floppy interface. In the past, some external floppy drives have been available in FireWire (IEEE 1394/i.LINK) or even parallel interfaces as well. Disk Physical Specifications and Operation
Most laptops sold today are equipped with a 3 1/2-inch 1.44MB floppy disk drive either as standard equipment or as an option. These drives are similar to the 5 1/4-inch 1.2MB drives found on old desktops. A few older laptops have a 2.88MB 3 1/2-inch drive that can also read and write 1.44MB disks. The physical operation of a disk drive is fairly simple to describe. The disk rotates in the drive at either 300rpm or 360rpm. Most drives spin at 300rpm; only the 5 1/4-inch 1.2MB drives spin at 360rpm. With the disk spinning, the heads can move in and out approximately 1 inch and write 80 tracks. The tracks are written on both sides of the disk and are therefore sometimes called cylinders . A single cylinder comprises the tracks on the top and bottom of the disk. The heads record by using a tunnel-erase procedure that writes a track to a specified width and then erases the edges of the track to prevent interference with any adjacent tracks. Different drives record tracks at different widths. Table 10.23 shows the track widths in both millimeters and inches for the various types of floppy disk drives found in modern PC systems. Table 10.23. Floppy Disk Drive Track-Width Specifications
How the Operating System Uses a Disk
To the operating system, data on a floppy disk is organized in tracks and sectors, just as on a hard disk drive. Tracks are narrow, concentric circles on a disk. Sectors are pie-shaped slices of the individual tracks. Table 10.24 summarizes the standard disk formats for PC floppy disk drives. Table 10.24. 5 1/4-Inch and 3 1/2-Inch Floppy Disk Drive Formats
You can calculate the capacity differences between various formats by multiplying the sectors per track by the number of tracks per side together with the constants of two sides and 512 bytes per sector. Note that the floppy disk's capacity can actually be expressed in various ways. For example, what we call a 1.44MB disk really stores 1.475MB if you go by the correct decimal prefix definition for mega(byte). The discrepancy comes from the fact that in the past floppies were designated by their kilobinary (1,024 byte) capacity, which in the past we abbreviated KB. The current abbreviation for kilobinary is KiB according to the International Electrotechnical Commission (IEC). Despite the IEC standards, the traditional method when discussing floppy drives or disks is to refer to the capacity of a floppy by the number of kilobinary bytes (1,024 bytes equals 1KiB) but to use the otherwise improper abbreviation KB instead. This was also improperly extended to the abbreviation MB, such that a disk with an actual capacity of 1,440 KiB capacity was instead denoted as a 1.44MB disk, even though it would really be 1.406 MiB (megabinary bytes) or 1.475MB (million/megabytes) if we went by the correct definitions for MiB (mebibyte) and MB (megabyte). For the remainder of this chapter, I will refer to the capacity of the various floppy disks according to the previously used conventions rather than the more technically accurate IEC-designated binary and decimal prefixes.
Note Again, as with hard disk drives, both megabyte and millions of bytes have been improperly abbreviated as MB or M, often resulting in a great deal of confusion. The IEC prefixes for binary multiples was designed to eliminate this confusion. For more information on the 1998 IEC prefixes for binary multiples , see http://physics.nist.gov/cuu/Units/binary.html.
Like blank sheets of paper, new, unformatted disks contain no information. Formatting a disk is similar to adding lines to the paper so you can write straight across. Formatting the disk writes the information the operating system needs to maintain a directory and file table of contents. On a floppy disk, no distinction exists between a high-level and low-level format, nor do you have to create any partitions. When you format a floppy disk with Windows Explorer or the command prompt FORMAT.COM program, both the high- and low-level formats are performed at the same time. When you format a floppy disk, the operating system reserves the track nearest to the outside edge of a disk (track 0) almost entirely for its purposes. Track 0, Side 0, Sector 1 contains the Volume Boot Record (VBR), or Boot Sector, that the system needs to begin operation. The next few sectors contain the file allocation tables (FATs), which keep records of which clusters or allocation units on the disk contain file information and which are empty. Finally, the next few sectors contain the root directory, in which the operating system stores information about the names and starting locations of the files on the disk. Note that most floppies today are sold preformatted. This saves time because the formatting can take a minute or more per disk. Even if disks come preformatted, they can always be reformatted later. Cylinders
The cylinder number is usually used in place of the track number because all floppy drives today are double-sided. A cylinder on a floppy disk includes two tracks: the one on the bottom of the disk above Head 0, and the one on the top of the disk below Head 1. Because a disk cannot have more than two sides and the drive has two heads, there are always two tracks per cylinder for floppy disks. Hard disk drives, on the other hand, can have multiple disk platters ”each with two heads ”resulting in many tracks per single cylinder. The simple rule is that there are as many tracks per cylinder as there are heads on the drive. Cylinders are discussed in more detail in Chapter 9, "Hard Disk Storage." Clusters or Allocation Units
A cluster also is called an allocation unit . The term is appropriate because a single cluster is the smallest unit of the disk that the operating system can allocate when it writes a file. A cluster or allocation unit consists of one or more sectors ”usually a power of 2 (1, 2, 4, 8, and so on). Having more than one sector per cluster reduces the FAT size and enables the OS to run more quickly because it has fewer individual clusters to manage. The tradeoff is in some wasted disk space. Because the OS can manage space only in the cluster size unit, every file consumes space on the disk in increments of one cluster. Table 10.25 lists the default cluster sizes used for various floppy disk formats. Table 10.25. Default Cluster and Allocation Unit Sizes
Types of Floppy Disk Drives
The characteristics of the floppy disk drives you might encounter in PC-compatible systems are summarized in Table 10.26. As you can see, the different disk capacities are determined by several parameters, some of which seem to remain constant on all drives, although others change from drive to drive. For example, all drives use 512-byte physical sectors, which is true for hard disks as well. Table 10.26. Floppy Disk Logical Formatted Parameters
1.44MB 3 1/2-Inch Drive
The 3 1/2-inch, 1.44MB, high-density (HD) drives first appeared from IBM in its desktop PS/2 product line introduced in 1987. IBM had introduced a lower capacity 720KB version of this drive a year earlier in its first laptop, the IBM Convertible. Most other computer vendors started offering the drives as an option in their systems immediately after IBM. This type of floppy drive is still the most popular in systems today. The drive records 80 cylinders consisting of two tracks each, with 18 sectors per track, resulting in a formatted capacity of 1.44MB. Some disk manufacturers label these disks as 2.0MB, and the difference between this unformatted capacity and the formatted usable result is lost during the format. Note that the 1,440KB of total formatted capacity does not account for the areas the FAT file system reserves for file management, leaving only 1,423.5KB of actual file-storage area. The drive spins at 300rpm, and in fact must spin at that speed to operate properly with existing high- and low-density controllers. To use the 500KHz data rate (the maximum from most standard high- and low-density floppy controllers), these drives must spin at a maximum of 300rpm. If the drives were to spin at the faster 360rpm rate of the 5 1/4-inch drives, they would have to reduce the total number of sectors per track to 15; otherwise, the controller could not keep up. In short, the 1.44MB 3 1/2-inch drives store 1.2 times the data of the 5 1/4-inch 1.2MB drives, and the 1.2MB drives spin exactly 1.2 times faster than the 1.44MB drives. The data rates used by both of these HD drives are identical and compatible with the same controllers. In fact, because these 3 1/2-inch HD drives can run at the 500KHz data rate, a controller that can support a 1.2MB 5 1/4-inch drive can also support the 1.44MB drives. Other Floppy Drive Types
Other types of floppy drives that have been used in the past include the following:
Analyzing 3 1/2'' Floppy Disk Construction
The 3 1/2'' disks differ from the older 5 1/4'' disks in both construction and physical properties. The flexible (or floppy) disk is contained within a plastic jacket. The 3 1/2'' disks are covered by a more rigid jacket than are the 5 1/4'' disks. The disks within the jackets, however, are virtually identical except, of course, for size. The 3 1/2-inch disks use a much more rigid plastic case than older 5 1/4-inch disks, which helps stabilize the magnetic medium inside. Therefore, these disks can record at track and data densities greater than the 5 1/4-inch disks (see Figure 10.21). A metal shutter protects the media-access hole. The drive manipulates the shutter, leaving it closed whenever the disk is not in a drive. The medium is then completely insulated from the environment and from your fingers. The shutter also obviates the need for a disk jacket. Figure 10.21. Construction of a 3 1/2-inch floppy disk.
Because the shutter is not necessary for the disk to work, you can remove it from the plastic case if it becomes bent or damaged. Pry it off the disk case; it will pop off with a snap. You also should remove the spring that pushes it closed. Additionally, after removing the damaged shutter, you should copy the data from the damaged disk to a new one. Rather than an index hole in the disk, the 3 1/2-inch disks use a metal center hub with an alignment hole. The drive "grasps" the metal hub, and the hole in the hub enables the drive to position the disk properly. On the lower-left part of the disk is a hole with a plastic slider ”the write-protect/enable hole. When the slider is positioned so the hole is visible, the disk is write-protected ”the drive is prevented from recording on the disk. When the slider is positioned to cover the hole, writing is enabled, and you can save data to the disk. For more permanent write-protection, some commercial software programs are supplied on disks with the slider removed so you cannot easily enable recording on the disk. This is exactly opposite of a 5 1/4-inch floppy, in which covered means write-protected, not write-enabled. On the other (right) side of the disk from the write-protect hole usually is another hole called the media-density-selector hole. If this hole is present, the disk is constructed of a special medium and is therefore an HD or ED disk. If the media-sensor hole is exactly opposite the write-protect hole, it indicates a 1.44MB HD disk. If the media-sensor hole is located more toward the top of the disk (the metal shutter is at the top of the disk), it indicates an ED disk. No hole on the right side means that the disk is a low-density disk. Most 3 1/2-inch drives have a media sensor that controls recording capability based on the absence or presence of these holes. The actual magnetic medium in both the 3 1/2-inch and 5 1/4-inch disks is constructed of the same basic materials. They use a plastic base (usually Mylar) coated with a magnetic compound. High-density disks use a cobalt-ferric compound; extended-density disks use a barium-ferric media compound. The rigid jacket material on the 3 1/2-inch disks has occasionally caused people to believe incorrectly that these disks are some sort of "hard disk" and not really a floppy disk. The disk cookie inside the 3 1/2-inch case is just as "floppy" as the 5 1/4-inch variety. Floppy Disk Types and Specifications
This section examines the types of disks that have been available to PC owners over the years. Especially interesting are the technical specifications that can separate one type of disk from another, as Table 10.27 shows. The following subsections define all the specifications used to describe a typical disk. Table 10.27. Floppy Disk Media Specifications
Density
Density , in simplest terms, is a measure of the amount of information that can be reliably packed into a specific area of a recording surface. The keyword here is reliably . Disks have two types of densities: longitudinal density and linear density. Longitudinal density is indicated by how many tracks can be recorded on the disk and is often expressed as a number of tracks per inch (TPI). Linear density is the capability of an individual track to store data and is often indicated as a number of bits per inch (BPI). Unfortunately, these types of densities are often confused when discussing different disks and drives. Media Coercivity and Thickness
The coercivity specification of a disk refers to the magnetic-field strength required to make a proper recording. Coercivity, measured in oersteds, is a value indicating magnetic strength. A disk with a higher coercivity rating requires a stronger magnetic field to make a recording on that disk. With lower ratings, the disk can be recorded with a weaker magnetic field. In other words, the lower the coercivity rating, the more sensitive the disk. HD media demands higher coercivity ratings so the adjacent magnetic domains don't interfere with each other. For this reason, HD media is actually less sensitive and requires a stronger recording signal strength. Another factor is the thickness of the disk. The thinner the disk, the less influence a region of the disk has on another adjacent region. The thinner disks, therefore, can accept many more bits per inch without eventually degrading the recording. Handling/Caring for Floppy Disks and Drives
Most computer users know the basics of disk care. Disks can be damaged or destroyed easily by the following:
Despite all these cautions , disks are rather hardy storage devices. For maximum reliability, store 3 1/2-inch disks in an environment between 40 ° and 127 ° Fahrenheit, and store 5 1/4-inch disks in an environment between 40 ° and 140 ° Fahrenheit. In both cases, humidity should not exceed 90%. Airport X-Ray Machines and Metal Detectors
One of my favorite myths to dispel is that the airport X-ray machine somehow damages disks. I have a great deal of experience in this area from having traveled around the country for the past 20 years or so with disks and portable computers in hand. I fly about 150,000 miles per year, and my portable computer equipment and disks have been through X-ray machines hundreds of times. X-rays are essentially just a form of light, and disks and computers are not affected by X-rays at anywhere near the levels found in these machines. What could potentially damage your magnetic media is the metal detector. Metal detectors work by monitoring disruptions in a weak magnetic field. A metal object inserted in the field area causes the field's shape to change, which the detector observes. This principle, which is the reason the detectors are sensitive to metal objects, can be dangerous to your disks; the X-ray machine, however, is the safest area through which to pass either your disk or your computer. The X-ray machine is not dangerous to magnetic media because it merely exposes the media to electromagnetic radiation at a particular (very high) frequency. Blue light is an example of electromagnetic radiation of a different frequency. The only difference between X-rays and blue light is in the frequency, or wavelength, of the emission. Some people worry about the effect of X-ray radiation on their system's EPROM (erasable programmable read-only memory) chips. This concern might actually be more valid than worrying about disk damage because EPROMs are erased by certain forms of electromagnetic radiation. In reality, however, you do not need to worry about this effect either. EPROMs are erased by direct exposure to very intense ultraviolet light. Specifically, to be erased, an EPROM must be exposed to a 12,000 uw/cm 2 UV light source with a wavelength of 2,537 angstroms for 15 “20 minutes, and at a distance of 1 inch. Increasing the power of the light source or decreasing the distance from the source can shorten the erasure time to a few minutes. The airport X-ray machine is different by a factor of 10,000 in wavelength. The field strength, duration, and distance from the emitter source are nowhere near what is necessary for EPROM erasure. Many circuit-board manufacturers even use X-ray inspection on their circuit boards (with components including EPROMs installed) to test and check quality control during manufacture. Now, you might not want to take my word for it, but scientific research has been published that corroborates what I have stated. A few years ago, a study was published by two scientists ”one of whom actually designs X-ray tubes for a major manufacturer. Their study was titled "Airport X-rays and Floppy Disks: No Cause for Concern" and was published in 1993 in the journal Computer Methods and Programs in Biomedicine . Here's an excerpt from the abstract: A controlled study was done to test the possible effects of X-rays on the integrity of data stored on common sizes of floppy disks. Disks were exposed to doses of X-rays up to seven times that to be expected during airport examination of baggage. The readability of nearly 14 megabytes of data was unaltered by X-irradiation, indicating that floppy disks need not be given special handling during X-ray inspection of baggage. In fact, the disks were retested after 2 years of storage, and there still has been no measurable degradation since the exposure. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||