Floppy Disk Drive (PDF)

Report as inappropriate Your report has been received

Shared by: dizapam

Tags

Floppy, drive

Stats

views:: 56
posted:: 9/23/2011
language:: Danish
pages:: 28

Public Domain

Document Sample

PPT/2K804/04
Revision no.: PPT/2K403/02

Floppy Disk Drive
Revision no.: PPT/2K804/04

Introduction

Common devices used

for most data storage

• Magnetic tape

• Floppy disk

• Hard disk

• Optical disk like CD

ROMs.

© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

Floppy disk and its structure

• 3.5 Inches 1.44 MB floppy disk

• The disk is soft, thin and round made of Mylar or some other
plastics material coated with a magnetic medium.

• It is this magnetic medium that stores information in the digital
form (0’s and 1’s).

• The entire disk is covered by a hard plastic cover that protects
it from external damage that could be in the form of moisture,
dust or other magnetic fields.

© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

Floppy disk and its structure (contd.)

• This hard plastic cover has a small rectangular opening at one

corner that has a small plastic tab fitted in it. This is called the

"write protect" of a floppy.

• When the diskette is write protected a user cannot write or

erase any information on the diskette. He can only read from it.

• The floppy disk is organized into concentric circles which are

called tracks.

© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

Floppy disk and its structure (contd.)

• Each track is divided into pie shaped sections
called sectors.

• Group of sectors are called as Block

• Group of Blocks are called as Clusters.

Boot sector, File allocation table
(FAT), Root directory structure

© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

Floppy disk and its structure (contd.)

• All sectors hold the same amount of data i.e. 512 bytes.

• For storing data space is allocated as needed in groups of
sectors called clusters.

• A floppy disk, also called diskette's, has two sides.

• Data can be written to or read from either side.

• The first side is identified as side 0, and the second as side 1.

• The mechanism that actually performs the reading and writing
operation is called the read/write head.

© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

Floppy disk and its structure (contd.)

• The disk is logically divided into system area and data area

• Physically the system area starts from sector 1 track0 and

continues on to some part of track1.

• The data area follows after the system area.

• The operating system uses the system area

• The data area is used to actually store the data.

• Data area is larger than the system area.

© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

Floppy disk and its structure (contd.)

• The system area is further sub-divided into the following

• Boot sector consist of
– Bootstrap routine

– BIOS parameter block (BPB).

• The bootstrap routine checks to see if the disk contains a copy
of the two system files, IO.sys and Msdos.sys.

• The bootstrap reads these files into the memory and transfers
the control to the IO.sys.

© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

Floppy disk and its structure (contd.)

• The BPB holds the information about the disk’s physical

characteristics which is used by the device driver.

• FAT is the part of the system area that the DOS uses to keep

the track of files stored in the disk.

• FAT is so important that DOS creates two copies of a FAT.

• If one gets corrupted DOS uses the second copy.

© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

Information contained in the BIOS parameter block
in the boot sector.

© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04
Illustration of how FAT entries are
chained together

• File A starts in cluster2 and then
continues in cluster8.
• The entry of cluster8 points to
cluster11, which in turn points to
cluster12, where the file ends.
• This file is split-up into four clusters
• Three of which are not in sequence.
• File B is less fragmented, occupying
clusters 3, 4, 5, 6, 7,9 and 10.
• The entry for cluster7 points to cluster
9, where the file continues. Cluster9
points to 10 which contains the EOF
value.
© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

Illustration of how FAT entries are
chained together (contd.)

Various entries which contain the following information about
files and subdirectories in the root directory follows after FAT.
File name 8 bytes
Attribute 1 byte
Time of creation 2 bytes
Note :
Starting FAT entry 2 bytes
The Capacity of a
Extension 3 bytes floppy disk can be
Reserved 10 bytes calculated as :-
Date of creation 2 bytes No. of HEADS x
No. of TRACKS x
File size 4 bytes No. of Sector x
No. of Bytes/sector.

© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

Illustration of how FAT entries are
chained together (contd.)
Different types of diskettes used in PCs.

© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

Mechanical parts of a floppy disk drive

• Read/Write Head

• The read/write is built around a core of soft iron.

• A coil of wire is wrapped around this core.

• This coil is actually tapped in the center, so that it behaves as
if it were two separate coils.

• When the control circuits want to write something on the
diskettes, they send a current through these coils.

• This creates electro-magnetic lines of force in the soft iron
material.
© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

Mechanical parts of a floppy disk drive (contd.)

• The “air gap” at the bottom of the core acts to focus this force

on the oxide layer on the surface of the diskette.

• This creates a magnetized spot on the oxide layer.

• When the control circuits want to read from the disk, the

process is reversed.

• As the magnetized spots pass under the head they induce

lines of force in the soft iron core, which then create tiny

current in the coils of wire.
© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

Mechanical parts of a floppy disk drive (contd.)

Head Loading Mechanism

© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

The 3. 5 inch drive clamping mechanism

• Hold the disk assembly firmly in position.

• First, slides the disk onto the drive.

• A metal plate is suspended above the disk assembly.

• When the disk is inserted, this plate is lowered, clamping the
hub of the disk against the top of the drive motor.

• The motor-control circuit turns the motor on and off.

• As the motor turns, a sensor detects its speed and reports
back to the control circuit.

© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

The 3. 5 inch drive clamping mechanism (contd.)

Disk clamping

© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

The Drive Control Circuitry

• Designed around a large IC called a Floppy Disk controller IC.
(IC -765)
• The FDC is connected to the data bus of the main computer.
• When the computer wants to write something onto the disk, it
places the data onto the data bus and strobes the Write
Enable line.
• The FDC converts the 8-bit parallel data to stream of serial bits
on the Write Data line.
• The computer strobes the Read Enable line when it wants to
read from the disk.

The Drive Control Circuitry (contd.)

Signal description for FDC to FDD interface.

The Drive Control Circuitry (contd.)

• Sensors

• Write-Protect
– Prevents the drive from writing to a disk when a disk is Write-
protected .

– Usually, the drive includes a switch which can sense the status of
a Write-protect opening on the case of the disk.

• Track 0 detector
– It is tripped when the head is reading the outermost track on the
disk.
© CMS INSTITUTE, 2006. All rights reserved. No part of this material may be reproduced, stored or emailed without the prior permission of Programme Director, CMS Institute
Revision no.: PPT/2K804/04

The Drive Control Circuitry (contd.)

• Index sensor
– Generates a pulse each time the disk completes a revolution.

• Disk change sensor

– Used to tell the control circuits when a disk has been inserted into
the disk drive.

Floppy Disk Drive Cable

• All floppy disk drives are connected to the motherboard's
external data bus by a 34-lead ribbon cable.
• Early PC BIOS logic was developed to recognize one or two
floppy disk drives.
• Floppy disk drive is installed on the end connector (near the
twist) is logically designated as the first or primary or A drive
by the BIOS.and
• The drive attached in the middle of the cable is always the
secondary or B drive. The BIOS will not recognize a B drive
unless an A drive is physically installed.

Floppy Disk Drive Cable (contd.)

• If you ever run into a situation with a two-floppy system where
you want to turn the A: drive into the B: drive or vice versa,
you can accomplish this easily through CMOS settings.

Troubleshooting Floppy Disk Drive

• To resolve a problem when a floppy disk drive stops working,
the steps are
– Check the floppy disk.

– Check for data errors on the disk.

– Check the CMOS setting.

– Check the floppy controller.

– Check the cable.

– Replace the floppy drive.

Creation of basic boot disk in Windows 98

• One can create the boot disk graphically or by using the
command prompt.

• Using the command prompt
– Insert a floppy disk into the drive.

– Give the command
FORMAT A: /S

• Graphically it can be done in Windows 98 as
– Open the Control Panel, click Add/Remove programs, choose
Startup Disk tab, and select the Create Disk Option.

DOS Errors

Design & Published by:
CMS Institute, Design & Development Centre, CMS House, Plot No. 91, Street No.7,
MIDC, Marol, Andheri (E), Mumbai –400093,
www.cmsinstitute.co.in