DPW

ET127

PC

TECHONOLOGY

Floppy & Hard Disk Drives

Unit 4

DPW

ET127

PC

TECHONOLOGY

Disk Drives• Hard disk drive - Sealed case containing

rotating disks and read/write heads• Floppy disk drives - 3 1/2” double-density or

high density disks• All disks store data in basically the same

way• Disks start out as blank disks of magnetically

coated plastic (floppies) or magnetic metal media

DPW

ET127

PC

TECHONOLOGY

Floppy Drive and Disk

DPW

ET127

PC

TECHONOLOGY

Disk Management

• Before you can store data on a new disk, you must perform the following tasks – Create partitions on a basic disk or create

volumes on a dynamic disk– Format the disk with a file system

(FAT,FAT32,NTFS, EXT3)

• A disk must be formatted before data can be written to the disk

DPW

ET127

PC

TECHONOLOGY

Partitions

• A new hard drive must first be divided in the proper size segments required by the operating system called partitions

• A partition is a physical section of a hard drive that creates a logical volume

• Each physical drive contains a partition table that shows the starting and ending address of each partition

DPW

ET127

PC

TECHONOLOGY

• A jump instruction• Name & versions of the OS files• Data structure which describes the

physical characteristics of the partition• Data structure which describes the

location of the file index• The bootstrap code

Boot Sector Information

DPW

ET127

PC

TECHONOLOGY

Formatting Disks/Drives

• 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 indexing format

• Creates the root directory

DPW

ET127

PC

TECHONOLOGY

Formatting Hard Drives• Hard drives are formatted twice• Low-level format - physically formats the

hard drive and creates tracks and sectors

• Operating system format -creates the boot record, File index and root directory on the disk

• Each partition on a drive has its own boot record, two copies of its file index and a root directory

DPW

ET127

PC

TECHONOLOGY

File Systems• The function of a file system is to map

data so it may be retrieved.• A file system must know the physical

location of data on the disk to be able to retrieve it

• Common file systems• FAT 16 partitions– up to 4 GB• Fat 32 partitions - up to 2 TB• NTFS partitions - up to 16 EB

DPW

ET127

PC

TECHONOLOGY

FAT16 File System• A very simple file system

• Designed for floppy and small disks

• FAT16 partitions can be no larger than 4 GB (2 GB for DOS)

• Can set permissions only on folders shared across network

• Cannot set permissions on files available locally

DPW

ET127

PC

TECHONOLOGY

FAT16 Benefits• Cross-platform availability• Compatible with number of other OSs• Good for disaster recovery because it

gives you a back door to the disk• Low overhead• Does not need to maintain space for a

transaction log

DPW

ET127

PC

TECHONOLOGY

FAT16 Disadvantages• Name must begin with letter or number

• Name cannot contain "/\:;|=,^*?

• Name cannot contain any spaces

• Uses 8.3 naming convention

• Does not support long file names

• Device names are reserved

• Root directory can only contain 512 entries

DPW

ET127

PC

TECHONOLOGY

FAT32 Advantages• FAT32 can support partitions up to 2 TB• It is more efficient in terms of allocating

sectors to clusters• The BIOS Parameter Block partition is larger• The boot sector stores a count of free clusters

on the partition• Does not store root directory in a set area• Uses an ordinary cluster chain• Extended partitions can hold up to 32 logical

volumes

DPW

ET127

PC

TECHONOLOGY

FAT32 Disadvantages• Not supported by all operating systems

• Only Primary partitions are bootable

• Must use FAT16 or VFAT to format shared partitions in a mixed operating system environment

• Only Windows 95 OSR2, Windows 98, ME, XP and 2000 support FAT32

DPW

ET127

PC

TECHONOLOGY

NTFS File System• Can support partition sizes up to 16 EB

• Organizes the data on disk with a relational database

• Everything on the volume is considered an object

• Every file stored on the volume is represented in a record

• Properties called streams can be added to the objects

DPW

ET127

PC

TECHONOLOGY

NTFS Advantages• Root directory can contain unlimited entries

• Supports File level security

• Supports File level encryption

• Supports Disk quotas

• Provides POSIX support

• Supports individual file compression - every file except NTLDR can be compressed

• Allows auditing

• Supports transaction logging

• Tracks ownership

• Can store files in non-contiguous memory

DPW

ET127

PC

TECHONOLOGY

NTFS Disadvantages

• Not compatible with other operating systems

• No back door access - good for security, bad for administrators

• Requires space and processing for the transaction log

DPW

ET127

PC

TECHONOLOGY

Disk Physical Characteristics

• Sector - The segment of a track that falls within the pie-shaped wedge that holds 512 bytes of data

• Cluster - the smallest unit allocated for a file can be read from or written to a disk at on time and sometimes called file allocation units

• Clusters contain one or more sectors

DPW

ET127

PC

TECHONOLOGY

Logical Hard Drive• Tracks

– Concentric Circles• Cylinder

– Same track through all platters

• Sectors– Pie Wedge Divisions

- equal in size• Clusters

– Group of sectors– Smallest area data

can be written to

DPW

ET127

PC

TECHONOLOGY

Master Boot Record• Located at track 0, sector 1

• Contains a physical layout of the disk

• When the disk was formatted

• How the disk was formatted

• What operating system was used

• Points to the operating system loader code

DPW

ET127

PC

TECHONOLOGY

Partitions

• Partitions are assigned either a volume name or a drive letter

• Primary partitions can be made active partitions but can only be assigned a single drive letter or volume name

• Extended partitions cannot be made active but can be divided up into several logical drives with each assigned a drive letter

• There can be a maximum of four partitions on a physical hard drive (4 primary or 3 primary and 1 extended)

DPW

ET127

PC

TECHONOLOGY

• 64-byte data structure

• Located in first sector of the hard disk

• Contains info about disk partitions

• Can define up to 4 partitions per disk

• Partition Table Entries contain info on

–Whether the partition is a system partition

–Where the disks begins and ends

–Total number of sectors used

–The partition’s file system

Partition Table

DPW

ET127

PC

TECHONOLOGY

Primary Partitions

• Only a primary partition can be marked as the active partition

• The active partition is where the hardware looks for the boot files to start the operating system

• Multiple primary partitions allow you to isolate different operating systems or types of data

DPW

ET127

PC

TECHONOLOGY

Extended Partitions

• There can be only one extended partition on a hard disk

• Unlike primary partitions, you don't format extended partitions or assign drive letters to them

• You divide extended partitions into segments. Each segment is a logical drive where you assign a drive letter to each logical drive and format it with a file system

DPW

ET127

PC

TECHONOLOGY

Primary and Extended PartitionsPrimary Partitions

F:F:

E:E:

D:D:

C:C:

G:

E:E:

D:D:

C:C:

PhysicalDrive

ExtendedPartitionwith LogicalDrives

PrimaryPartitions

OR

F:

H:

DPW

ET127

PC

TECHONOLOGY

Assigning Drive Letters

Disk 0

Disk 1

Disk 2

Disk 3

C:I:

C:I:

F:F:G:G:H:H:

D:D:

E:E:

Assigned

Primary

Primary

Primary

Logical

DPW

ET127

PC

TECHONOLOGY

Volume Sets

D:D:150 MB150 MB

Disk 0

Disk 1

Physical Disks Logical Disks

C:C:150 MB150 MB

F:150 MB

E:E:50 MB50 MB

Free Space100 MB

D:D:150 MB150 MB

C:C:150 MB150 MB

Free Space50 MB

E:E:50 MB50 MB

DPW

ET127

PC

TECHONOLOGY

Hard Drive Components• The hard drive contains read/write

heads and 2 or more spinning platters• The hard drive requires a controller

board filled with ROM programming to instruct the heads how, where, and when to move across the platters

• Integrated device electronics (IDE) drives have large capacity, are easy to install, and are competitively priced

DPW

ET127

PC

TECHONOLOGY

Physical Hard Drive• Spindle

– Drive rotates on this

• Platters– Physical

metal disks– Data records

on both sides• Read/Write

Head– Ride above

the platters, rearranging magnetic particles

DPW

ET127

PC

TECHONOLOGY

Hard Disk Anatomy

DPW

ET127

PC

TECHONOLOGY

Hard Drive Fan

DPW

ET127

PC

TECHONOLOGY

Access Time• Average Time to retrieve data, in

milliseconds• Average Seek - Amount of time for the

read/write head to find the track/cylinder that holds the desired data

• Settling Time - Time required for the head to become stable over the location of the data

DPW

ET127

PC

TECHONOLOGY

Access Time

• Latency - Amount of time for the disk to rotate under the read/write head until the data appears underneath it

• Average Access = Average Seek + Settling Time + Latency– Many manufacturers will not figure in

the total formula when printing out this spec

DPW

ET127

PC

TECHONOLOGY

Hard Drive Specifications• Data Buffer Size

– Amount of memory on drive for temporary storage of data during transfer from drive to memory (and vice versa)

• Transfer Rate– Rate that info is dumped to the controller

from the drive• Interleave

– Allows a drive to jump sectors in read/write– Used to slow down for older system

DPW

ET127

PC

TECHONOLOGY

Fragmentation• After a hard drive has been in use for

awhile, files tend to be written in a non-contiguous format which means that the clusters a file is written to are not in sequential order

• Slows down file access• Hard to recover file if becomes corrupt• DEFRAG is a utility corrects the

problem and optimizes the disk

DPW

ET127

PC

TECHONOLOGY

Clusters• Lost Clusters are clusters that no file

points to and occur as a result of the mapping in FAT becoming corrupted

• Cross-Linked Clusters are cluster that more than one file points to that occur as a result of the mapping in FAT becoming corrupted

• SCANDISK and similar programs will repair both of these problems

DPW

ET127

PC

TECHONOLOGY

Disk Compression• Using software to increase the amount

of disk space– Usually doubles the space

• Stores entire contents of drive as a single file

• Uses a mathematical algorithm to store files in a more compact format

• Files decompress “on-the-fly”• Slows down system performance

DPW

ET127

PC

TECHONOLOGY

Disk Caching

• A disk cache is a temporary storage area in RAM for data being read from or written to a hard drive

• Hardware cache is contained in RAM chips built right on the disk controller card

• Software cache is stored on the hard drive and loaded into memory as a terminate-and-stay-resident (TSR) program

DPW

ET127

PC

TECHONOLOGY

Disk Cloning

• Used to make a bit by bit copy of the entire hard disk or a single partition

• Independent of the operating or file system

• Software like Norton’s ghost or Drive Image

• Makes deploying identical workstations much easier

• Can also be used to backup computers

DPW

ET127

PC

TECHONOLOGY

Installing a Hard Drive• Set the drive jumpers for either master

or slave• Connect the data cable to the drive with

pin 1 usually toward the power connector• Attach the other end of the cable to the

motherboard or drive controller, aligning the edge color with pin 1

• Connect a power cable to the hard drive• Slide the hard drive into the rear of the

bay and secure it with two short screws on both sides of the bay

DPW

ET127

PC

TECHONOLOGY

Motherboard Connectors

DPW

ET127

PC

TECHONOLOGY

Hard Drive Jumpers

DPW

ET127

PC

TECHONOLOGY

System Backups• All users can backup a file or directory if

they have read permission• What Should be Backed Up? Always

– Critical files and folders– System configuration files

• Periodically– Files that rarely change

• Never– Temporary files

DPW

ET127

PC

TECHONOLOGY

Types of Backups• Full - backs up all selected files and

resets the archive bit• Copy - backs up all selected files but

does not reset the archive bit• Incremental - backs up all the selected

files that have changed and resets the archive bit

• Differential - backs up all the selected files that have changed but does not reset the archive bit

DPW

ET127

PC

TECHONOLOGY

Backup Schedule & Tape Rotation

• Typical Backup Schedule– Daily Incremental– Weekly Full– Month-End Full

• Typical tape rotation– Store daily tapes for 3 weeks on site than

reuse– Store weekly tapes for 6 months on site

than reuse– Store monthly tapes off-site for 2 years

than return and reuse

DPW

ET127

PC

TECHONOLOGY

Backup Terminology• Backup Sets - group of files and folders

from a single volume from a single backup operation

• Catalogs - lists of backup sets or members– Tape catalog - contains list of all backup

sets on a tape– Backup Set Catalog - contains list of files

and folders in the backup set• Backup Log - record of the entire

backup operation

DPW

ET127

PC

TECHONOLOGY

Malware• Viruses – malicious code that requires a host

program to run so it can replicate itself and can do anything from be annoying to completely trashing the computer

• Worms – self replicating code that overwhelms the system by its presence

• Trojan horses – a program that can either do damage or collect information and send it back to its master

• Logic bombs – code designed to damage the system triggered by a specific event

DPW

ET127

PC

TECHONOLOGY

Viruses Types

• Boot sector – can appear to be a hardware failure because it trashes the boot record

• File – attaches itself to a legitimate program such as a macro virus

• Multipartite – combination of a boot sector and file virus

DPW

ET127

PC

TECHONOLOGY

Virus Cloaking Methods

• Polymorphic – changes it signature as it replicates

• Encrypting – transforms itself into a non-replicating program to hide

• Stealth – monitors when it home is about to be opened and keeps an uninfected version handy to open

DPW

ET127

PC

TECHONOLOGY

Protection

• Use a good anti-virus program• Use common sense about

downloading files from the internet• Use a firewall to manage what ports

are open• Use an anti-spyware scanning program

DPW

ET127

PC

TECHONOLOGY

Recommended Maintenance

• Do regular backups• Use antivirus and anti-spyware

software• Periodically defrag the hard disks• Don’t smoke near your computer• Use a dehumidifier in damp areas• Use caution when moving the

computer if it is running