Floppy Drives and Other Essential Devices

1
Chapter 4

• Floppy Drives and Other Essential Devices

Managing and Maintaining Your PC
2
Floppy Drives

• 5 1/4 drives
• Double-density and high-density
• 3 1/2 drives -
• More prevalent than 5 1/4
• Hold more data than 5 1/4
• Double-density, high-density, and the very rare
  extra-high-density

3
Floppy Drives
Table 4-1 Floppy Disk Types
4
Floppy Drives

• The physical hardware of all disk drives looks
  and operates in much the same way
• Data cable connects the drive to a controller
  board (or to the systemboard)
• Controller board plugs into the system bus
• The board communicates with the CPU, passing data
  to and from the floppy disk
• Power is provided by the power supply

5
Floppy Drives
Figure 4-1 Floppy drive, data cable, and
power connection
6
Floppy Drives

• All floppy disks store data in much the same way
• Diskettes start out as blank disks of
  magnetically coated plastic
• Before data can be written to the disk, it must
  be formatted
• It is mapped out in concentric circles called
  tracks or cylinders
• The tracks are divided into pie-shaped wedges
  called sectors

7
Floppy Drives
Figure 4-2 3 1/2-inch disk showing tracks
and sectors
8
Read/Write Heads

• Data is written to and read from the disk via
  read/write heads
• Read/write heads are basically a magnetic
  mechanism in the floppy drive
• An actuator head holds 2 read/write heads - one
  head is above the disk, the other is below
• As the disk spins, the heads lightly touch the
  disks surface

9
Read/Write Heads
Figure 4-3 Uniform track widths are created by a
floppy drive read/write head
10
Disk Storage

• Sector - The segment of a track that falls within
  the pie-shaped wedge
• Holds 512 bytes of data
• Cluster - one or more sectors that are the
  smallest units allocated for a file
• The smallest unit of data that can be read from
  or written to a disk at on time
• Sometimes called file allocation units

11
Formatting Disks

• Formatting
• Creates tracks and sectors by writing a series of
  F6s, (which effectively erases any data on the
  disk), and sector address marks to identify the
  beginning sector on a track
• Creates the master boot record
• Creates 2 copies of the file allocation table
  (FAT)
• Creates the root directory

12
Formatting Disks - MBR

• Master boot record contains information that DOS
  later uses when it reads from the disk
• When the disk was formatted
• How the disk was formatted
• What version of DOS or Windows 95 was used
• Contains a uniform layout
• Located at track 0, sector 1

13
Formatting Disks - MBR
Table 4-2 Contents of the Master Boot Record
14
Formatting Disks - FAT

• File allocation table (FAT)
• Contains location of files on the disk
• Lists how each cluster or file allocation unit on
  the disk is currently being used
• Files may be in one or more clusters that may not
  be contiguous on the disk (Noncontiguous files
  are fragmented files)
• Cluster chain determines all cluster locations
  for a file on a disk

15
Formatting Disks - FAT
Figure 4-4 FAT with one file mapped on the disk
16
Formatting Disks - Root Directory

• Root directory
• A table listing all the files that are assigned
  to this table
• Contains a fixed number of rows, dependent upon
  the disk type
• Contains information about each file and
  subdirectory stored in it
• Only directory that limits the number of entries

17
Formatting Disks - Root Directory
Table 4-3 Root Directory Entries for Disk Types
18
Formatting Disks - Root Directory
Table 4-4 Root Directory Information for Each
File
19
Formatting Disks - Root Directory
Table 4-5 File Attributes for each Bit in the
Directory Attribute Byte (Reading from Left to
Right Across the Byte)
20
Managing Disks using DOS

• FORMAT command
• Prepares a disk for use
• LABEL command
• Changes the volume label or electronic name on a
  disk
• CHKDSK command
• Creates a status report of a disk and also
  reports on free conventional memory
• Can repair lost clusters in the FAT

21
FORMAT Command
FORMAT Options DESCRIPTION /V To enter Volume
label /S Writes System files to
disk /Q Quickly reformat a good
disk /Fsize Specifies size of disk if not
default Ex FORMAT A/F720 /U Unconditional
or complete format
Table 4-6 FORMAT Command Options
22
Managing Disks using DOS

• SCANDISK command
• Checks for lost and cross-linked clusters, does a
  surface scan for bad sectors, and may defragment
  the drive
• DEL or ERASE command
• Erases files or groups of files
• UNDELETE command
• May be used to try to recover deleted files on a
  disk area that has not be overwritten

23
Managing Disks using DOS

• RECOVER command
• Attempts to recover a file from damaged sectors
  on a disk
• DISKCOPY command
• Makes an exact duplicate of one disk to another
  disk of the same size and type
• COPY command
• Copies a single file or a group of files

24
Managing Disks using DOS

• XCOPY command
• More powerful than the COPY command
• Can be used to copy all files in a directory, and
  all subdirectories under the directory
• Can be used to copy files created or modified
  after a specified date
• DELTREE command
• Deletes a directory, its subdirectories, and all
  files within the subdirectories

25
Managing Disks using Windows 3.x File Manager

• Format a disk from the File Manager
• Click the Disk menu
• Click Format Disk
• Click the Capacity list arrow
• Select the correct disk type
• Other disk commands can be performed from the
  File Manager via the Disk menu

26
Managing Disks using Windows 3.x File Manager
Figure 4-5 Format a Disk from File Manager
27
Managing Disks using Windows 3.x File Manager
Figure 4-6 Disk menu in File Manager
28
Managing Disks using Windows 3.x File Manager
Table 4-7 Four Disk Menu Options Under File
Manager
29
Managing Disks using Windows 3.x File Manager
Figure 4-7 File menu in File Manager
30
Managing Disks using Windows 3.x File Manager
Table 4-8 Five File Menu Options Under File
Manager
31
Managing Disks using Windows 95

• Format a disk
• Click Start button on task bar
• Click Programs
• Click Windows Explorer
• Right-click on either drive A or drive B
• Click Format on the menu
• Select appropriate options

32
Managing Disks using Windows 95
Figure 4-8 Menu to manage a floppy disk
33
Managing Disks using Windows 95 - Copy a Disk

• If you select Copy Disk
• The disk listed under Copy from is the source
  disk
• The disk under Copy to is the destination disk
• Click Start to copy the disk

34
Managing Disks using Windows 95 - Copy a Disk
Figure 4-10 Copying a disk
35
Managing Disks using Windows 95 - Rescue Disk

• When you create a Windows 95 rescue disk, the
  disk is formatted and system files are copied to
  the disk
• In addition to the files necessary to boot the
  system, the files in Table 4-9 may also be copied
  to the disk

36
Managing Disks using Windows 95 - Rescue Disk
FILE PURPOSE Io.Sys Used to boot
DOS Msdos.Sys Startup configuration
Information Command.Com Provides DOS
prompt Attrib.Exe Changes the attributes of a
file Chkdsk.Exe Checks status of disk and
repairs Edit.Com DOS editor Fdisk.Exe Used to
Partition a hard drive Format.Exe Formats a disk
or hard drive Mem.Exe Displays memory
information Mscdex.Exe CD-ROM driver Scandisk.Exe
Checks and repairs disk drives Sys.Com Makes
a diskette or hard disk bootable
Table 4-9 Rescue Disk Files Created in Windows 95
37
Problems with Floppy Drives

• Over time, floppy drives may slowly shift out of
  alignment. With the proper software tools you
  can quickly check if a drive is working properly
  and test
• Azimuth skew - does the drive head align itself
  well with the tracks?
• Hub centering - does the disk wobble as it turns?
• Hysteresis - Can the drive find a track from any
  direction?

38
Problems with Floppy Drives

• Radial alignment - is the drive head centered on
  the track, or off to one side or the other?
• Rotation speed - does the drive turn the disk at
  the proper speed?
• Sensitivity - How far from the disk can the head
  be to read the data?
• Floppy drives are currently so inexpensive that
  they are usually replaced rather than repaired

39
Problems with Floppy Drives
Figure 4-11 Alignment of floppy drive heads
40
Problems with Floppy Drives

• Suggestions for solving problems
• Reinsert the disk
• Check drive for debris
• Be sure the disk is in the proper drive
• Try a different diskette in the drive
• Try to access the disk with different software
• Try the DIR and CHKDSK commands

41
Problems with Floppy Drives

• Does the drive light come on at all? It may be a
  hardware or software problem
• If there are two drives, verify that the other
  drive works
• Reboot the machine and try the drive again
• Make sure the CMOS settings are correct
• Clean the read/write heads
• Check all cable connections

42
Problems with Floppy Drives

• Replace the data cable
• Exchange the controller card
• Exchange the drive with a working one
• The problem may be with the systemboard or the
  ROM BIOS

43
Floppy Drive Error Messages

• Non-system disk or disk error. Replace and
  strike any key when ready.
• You are booting from a disk that does not have
  the OS on it (It is missing Command.Com,
  IO.Sys, MSDOS.Sys)
• Invalid or missing COMMAND.COM
• Boot from a disk that contains the correct
  version of COMMAND.COM

44
Floppy Drive Error Messages

• Incorrect DOS version
• You are using external DOS commands from a
  different version of DOS
• Invalid Drive Specification
• You are trying to access a drive the OS does not
  know is available
• Not ready reading Drive A, Abort, Retry,
  Fail?
• Disk is not inserted correctly possible bad boot
  record, FAT errors, or bad sectors

45
Floppy Drive Error Messages

• Track 0 bad, disk not usable
• Appears when you try to format a disk using the
  wrong disk type or size check your FORMAT
  command
• Write-protect error writing drive A
• Disk is write-protected. Be sure the
  write-protect window in the 3 1/2 disk is
  closed, or the write-protect notch on the 5 1/4
  disk is uncovered

46
Chapter Summary

• The essential input/output devices on a computer
  are disk drives, keyboard, monitor, and pointing
  device
• Floppy drives
• Must be formatted before they can be used
• Data is stored on disks in concentric circles
  called tracks
• Disks come in different sizes and capacities

47
Chapter Summary

• The smallest unit of space allocated to a file is
  called a cluster
• Command.Com and 2 hidden files must be on a disk
  to make it bootable
• DOS, Windows 3.x, Windows 95 have similar
  commands to manage floppy disks
• Floppy drives can be replaced or added to
  computers
• A twist in the data cable indicates to the
  computer which drive is drive A