This document discusses various components of computer storage systems. It describes how hard disks are formatted and partitioned to define where data is stored. It explains the differences between IDE, EIDE, SCSI, floppy disks, and CD-ROM drives. It also provides an overview of RAID configurations, how data is organized on disks, and basic concepts such as formatting, partitioning, disk compression, and backing up data.

1. Hard Disks
• Low-level format- organizes both sides of each
platter into tracks and sectors to define where
items will be stored on the disk.
• Partitioning: divide hard disk into separate
areas called partitions; each partition functions
as if it were a separate hard disk drive.
• High-level format defines the file allocation
table (FAT) for each partition, which is a table
of information used to locate files on the disk.

2. Storage Systems
• Hard Drives
– 2 Types: SCSI and IDE
• IDE drives-
– originally developed as alternative to more expensive SCSI
drives.
– Modern versions called EIDE drives.
– Support up to 4 multigigabyte drives.
– If you want more devices, use SCSI or USB
– Low-level formatted at the factory

3. Low Level Formatting
• Low level format scans disk for defects and
sets aside sectors with defects so they are not
used for data.
• IDE drives should never be low level
formatted by a user or technician. Only high
level format necessary.

4. Installing IDE/EIDE drives
• IDE supports TWO drives in a system
– one master (boot disk) and one slave
– set master and slave using jumpers
• EIDE supports FOUR drives per system
– 2 drives on each of 2 cables
– only one master, all others are slaves
• IDE and EIDE drives both use 40-pin ribbon
cable aligned to pin 1

5. Hard Drive

6. Floppies
• Two sizes
– 3.5 inch
– 5.25 inch
• 3.5 inch holds 1.44 MB for High density and
750 KB for Double Density
• Connected with 34 pin ribbon cable
• Two Floppy Drives possible
• Has twist in cable to distinguish A drive from
B drive

7. SCSI
• Pronounced Scuzzy
• Small Computer Systems Interface
• For wide range of peripheral devices, including hard
disks, tape drives, optical drives, CD-ROMs and disk
arrays.
• 8 devices can connect to a daisy chain
• This chain must be terminated at both ends
• Each device on chain is assigned unique device ID
number that is determined by jumpers or DIP
switches

8. Installing and configuring SCSI
• SCSI bus supports 8 devices
• There are eight SCSI IDs numbered 0 through
7
• ID 7 is always reserved for the SCSI host
adapter
• SCSI hard disk, if used as a boot drive, is
assigned SCSI ID 0
• If you have both IDE and SCSI hard drive,
IDE drive should be boot drive

9. Types of SCSIs
• SCSI 1- 5 MB transfer rate, Centronics 50 pin
or DB 25, has 8 bit bus
• SCSI 2 -also SCSI Fast Wide, includes 16 bit
bus , called Wide SCSI, and twice as fast
transfer rate
• SCSI 3- Includes Ultra SCSI, Wide Ultra
SCSI, and Ultra 2 SCSI, 16 bit bus with up to
80 MBps transfer rate

10. RAID
• Redundant Array of Independent Disks
• Category of disk drives that employs 2 or more
drives in combination for fault tolerance (error
recovery)
• 10 levels of RAID
• 3 on test will be:
• RAID 0, RAID 3, RAID 5

11. RAID continued
• RAID 0- Striped disk without parity
• RAID 3- Parallel transfer with parity
• RAID 5- Data striping with parity

12. How Data is Organized on Disk
• Tracks-
– circular areas of the disk
– Length of a track one circumference of disk
– Over 1000 on a hard disk
– Data first written to outer most track
• Sectors-
– Divides tracks sections
– On a floppy 9 sectors exits
• Cylinders-
– Logical groupings of the the same track on each disk surface in a disk
unit
• Clusters-
– Groups of sectors used by operating system
– 64 sectors in one cluster

13. Track=
concentric
circle
Sector =
small arc
of track
Can store
512 bytes
Tracks and sectors

14. Interleaving
• Allows the read/write head to use the rotation
of the disk to its advantage
• One sector is written to and the disk skips to
several sectors down

15. Formatting
• Low level formatting done at factory
– Builds the File Allocation Table (FAT)
– Physically scans the disk media for defects
• Remember FAT is always located at Track 0
• High level formatting is automatically done
during installation of operating system

16. Operating System File Systems
• DOS uses FAT
• Windows 3.x uses Virtual FAT
• Win 95 uses VFAT and FAT32
• Win NT uses NTFS

17. Partitioning
• FDISK command is used
• Divides hard drive into logical subdivisions
which are seen by the operating system as
separate logical hard disks.
• Hard drives divided into primary and extended
partitions. The primary partition boots the
system. Can have up to 4 primary partitions

18. Partitioning
• Extended can be divided up to 23 times on disk.
• Partitioning disks improves disk efficiency through
reduced cluster size.
• In DOS, Win 3x and early versions of Win 95 a hard
disk over 2 GB must be divided into smaller partions
• Now Win 95 and Win 98 can create a primary
partition of up to 8 GB
• Following partition, the first sector on cylinder 0
reserved for master boot record

19. Disk compression
• Reduce amount of space taken up by files by
substituting codes for repeating patterns of
data
• To access data on compressed disk, must load
disk compression utility into RAM first
• This disk compression utility works between
OS and disk controller to intercept requests
and compress or decompress files- the result is
slower disk access

20. Backing up data
• Archival: full backup- contains everything
from the hard disk
• Incremental: contains only files that have been
modified since last (previous) backup
• Differential: backs up all the data modified
since last full backup
• Copy backup: copy duplicate of file, directory,
or disk to another disk

21. CD ROM
• Capacity of 650 MB
• Transfer speeds of around 24X speed
– X refers to the transfer speed in the first CD ROM,
which was 150 K
• CD is the slowest device on PC
• When installing to IDE system must be
configured as slave
• WORM and EO