1. Lecture No 11 Storage Devices

2. Storage Involves Two Processes
Writing data
Reading data

3. Storage Media The materials on which data is stored.
The physical material on which data is stored is called a storage medium.
E.g. Diskette is a storage medium.

4. Storage Devices
The hardware that writes data to or reads data from a storage medium is called a storage device.
E.g. A floppy disk drive is a storage device.

5. Two Categories of Storage Technology
Magnetic storage
Optical storage

6. Magnetic Storage Diskettes Hard disks High-capacity floppy disks
Magnetic tape

7. Optical Storage Compact Disk Read-Only Memory (CD-ROM)
CD-Recordable (CD-R) CD-Rewritable (CD-RW)
Digital Video Disk Read-Only Memory (DVD-ROM)
DVD Recordable (DVD-R/DVD), DVD Rewritable (DVD-RW)
Photo CD

8. Magnetism Allows Data Storage
Hard disks, diskettes, high-capacity floppy disks and
tapes have a magnetic coating on their surface that
enables each medium to store data.

9. Magnetic Storage Devices How Magnetic Storage Works
A magnetic disk's medium contains iron particles, which can be polarized when given a magnetic charge in one of two directions.
Each particle's direction represents a 1 (on) or 0 (off), representing each bit of data that the CPU can recognize.
A disk drive uses read/write heads containing electromagnets to create magnetic charges on the medium.

10. Write head
Medium
Random particles
(no data stored)
Current flow
(write operation)
Organized particles
(represent data)

11. As the medium
rotates, the head
writes the data

12. Preparing Disks for Storage
Before a magnetic disk can be used, it must be formatted—a process that maps the disk's surface and determines how data will be stored.
During formatting, the drive creates circular tracks around the disk's surface, then divides each track into sectors.

14. Formatted Disks Have Three Sections
Main sections, called Tracks
Track subsections, called Sectors
Groups of sectors, called Clusters

15. Logical Format
A logical format is the labeling of tracks and
sectors.

16. The Logical Format has Four Disk Areas
Master boot record
File allocation table
Root folder
Data area

17. Master Boot Record (MBR)
This program determines whether the disk contains the basic components of an operating system necessary to run successfully.
Boot sector:
It stores the master boot record (MBR), a small program that runs when you first start (boot) the computer.

18. File Allocation Table (FAT)
A log created during the logical formatting process
that records the location of each file and status of
each sector on the disk.

19. Root Folder
The top folder or directory in the disk’s folder hierarchy.
Enables the user to store data on the disk in a logical way.

20. Data Area
Place where data or program files are actually
stored.

21. 3.5-inch Diskettes (Floppy Disks)
Diskettes are used to transfer files between computers as a backup medium.
Spin rate: 300 revolutions per minute (rpm)
Disk Density=Total no of Sectors * Total no of bytes that each sector can hold.
Storage Capacity of HD disks is 1.44 MB

22. Hard Disks Spin rate: from 3,600 to 15,000 rpm
Storage capacity ranges from several hundred MB to more than 200 GB
High rotational speed allows more data to be recorded. Why????

23. Tape Drives Commonly used for hard disk backup.
Sequential Access Drives

24. PC Cards
Used to connect new components like memory and expanding storage capacity to a computer.
Up to 512MB memory.

25. Two Ways to Measure Storage Device Performance
Average Access Time
Data Transfer Rate

26. Average Access Time
Amount of time the device takes to move its read/write heads to any spot on the medium.
Measurement should be an Average Time.
Important measure of performance for storage devices and memory.

27. Access Time Measured in Two Ways
Storage devices: milliseconds (ms)
Memory devices: nanoseconds (ns)

28. Examples of Average Access Time
Floppy Disk: 100 ms
Hard disk: 6 to 12 ms
High-performance hard disk: 4 or 5 ms
CD-ROM: 80 to 800 ms
Tape drives: slowest at a few seconds to a few minutes

29. Hard drives are the fastest
Data Transfer Rate
Amount of time it takes for one device to transfer data to another device.
Measured in units of data per second
Note: MBps= Megabytes/sec, Mbps =megabits/sec 8bits = 1 byte
Hard drives are the fastest
CD-ROM’s, slow
Floppies, the slowest

30. Optimizing Disk Performance When the PC’s performance slows down, disk maintenance, or disk optimization, can speed things up again

31. File or Data Compression
Technology for making files smaller to free up storage space.
File compression enables to store more data on a disk effectively increasing the disk’s capacity.
File Compression is performed by a software.
Utilities such as Windows' DriveSpace enable you to compress the entire contents of your hard disk.

32. File Compression Software
PKZIP and WinZip: Windows-based PC’s
StuffIT: Macintosh

33. Ways to Optimize Disk Performance
Delete temporary files
Uninstall little-used software programs
Run a disk scanner to look for and fix errors
Defragment the disk.

34. Drive-Interface Standards
Another factor to determine how quickly a drive can read and write data is the Type Of Controller that driver uses.
Storage Devices need a controller to act as an interface between the Drive and CPU.
Personal Computers use one of two drive-interface standards for built-in disk drives: EIDE or SCSI.
Other type of interface (USB & FireWire) to attach additional disk drives and other devices to a computer.

35. Drive-Interface Standards
EIDE -- Enhanced Integrated Drive Electronics
SCSI – Small Computer System Interface
USB – Universal Serial Bus
FireWire – IEEE 1394

36. EIDE Most new computer systems use EIDE drive-interface standard.
Latest version supports data transfer rates of 66MBps.
Variants: Fast IDE, ATA, Fast ATA, Ultra-ATA, ATA 66 etc.

37. SCSI
Earlier developed to connect third-party peripheral devices to mainframe computers.
Allows high data transfer rates than EIDE.
Supports 80MBps.
Normally found in Servers, Workstations etc.

38. USB & FireWire
All sort of peripheral devices can be attached to a computer through USB or FireWire port.
Support High Data transfer rates.