This document provides an overview of computer storage systems, including hard drives, floppy disks, SCSI, RAID, and CD-ROMs. It discusses how data is organized on disks using tracks and sectors. It also explains hard drive formatting, partitioning, and different file systems used by operating systems. Backup strategies like full, incremental, and differential backups are also summarized.

1. › Topic : Introduction Of Computer
Asif Jamal
Lecturer
Management Science
National University Of Modern
Languages (NUML)

2. 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.

3. 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

4. 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.

5. 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

6. Hard Drive

7. 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

8. 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

9. 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

10. 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

11. 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

12. RAID continued
› RAID 0- Striped disk without parity
› RAID 3- Parallel transfer with parity
› RAID 5- Data striping with parity

13. 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

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

15. 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

16. 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

17. Operating System File Systems
› DOS uses FAT
› Windows 3.x uses Virtual FAT
› Win 95 uses VFAT and FAT32
› Win NT uses NTFS

18. 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

19. 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

20. 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

21. 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

22. 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