1. Secondary Storage Rohit Khokher

2. Limitations of Primary Storage
Limited Capacity: It cannot be used to store the large volumes of data items.
Volatility: Looses data when electric power is turned off or interrupted.
Data Portability: It cannot be used to port the data from one place to other.
These limitations lead to the development of auxiliary memory or secondary storage devices.

3. Secondary Storage Devices
Sequential Access Devices
Direct Access Devices
Magnetic Tape
Magnetic Disk
Optical Disk
Floppy
Disk
Hard Disk
CD-ROM
WORM Disk
Disk Pack
Winchester Disk
ZIP
Disk

4. Magnetic Tape
The first truly mass auxiliary storage device was the magnetic tape drive
Tape drives have a
major problem; can
you describe it?

5. 7 Track;6-bit BCD; Even parity (all tracks must have even number of 1)
A frame
Track/Channel numbers 1 2 3 4 5 6 7 8 9 A B C D E F G H I J K L M N O P
Parity bit 7 6 5 4 3 2 1
zone
Numeric
6-bit BCD for letter A (Table 4.2 page 36
Even parity (all tracks must have even number of 1)
Error Checking

6. 9 Track;8-bit EBCDIC; Even parity (all tracks must have even number of 1)
EBCDIC for the letter A
Track/Channel numbers
A frame 1 1 2 3 4 5 6 7 8 9 A B C D E F G H I J K L M N O P 9 8 7 6 5 4 3 2 1
3’s digit
2’s digit
Added Zone
Zone
Parity bit
Unit’s digit
4’s digit
Error Checking
Odd parity (all tracks must have odd number of 1)
8-bit EBCDIC for letter A (Table 4.3 page 8

7. Terminologies Record: Group of characters separated by blank
Inter record gap (IRG)
Blocks: Records are grouped into blocks
Blocking factor: # of records perblocks
Inter Block gap (IBG)
Storage capacity of tape= Data recording density x Length
Data transfer rate (bytes/second to main memory
Tape drive
Tape controller
Tape Types (Half-inch tape reel, Half-inch tape cartridge, Quarter-inch streamer tape and 4mm Digital Audio Tape (DAT)

8. Advantages & Limitations of Magnetic Tape
Virtually unlimited storage capacity.
Low cost.
Easy to handle and store.
Easy to port.
Limitations
The are not suitably for frequent data access.
Must be operated in dustless environment.
Must be operated in controlled environment.
Must have proper identification labels

9. Uses of Magnetic Tape
Good for applications that require sequential data processing.
Data backup.
Data archiving.
Physically large data transfer
Software distribution

10. Magnetic Disks
Generally 8 bit EBCDIC code is used to record the data items.
Surface: 2 surfaces per disk.
Tracks:
Sectors: 8 sectors per track.
Disk pack: 200 disks.
Cylinder: Each track from all recording surfaces in a disk pack form a cylinder.
Storage capacity = # of surfaces × # of tracks per surface x # of sectors per track x # of bytes per sector.
Access mechanism: Read/write head moves to an address by specifying the (disk #, track #, sector #, byte #)
A platter coated with iron oxide: A magnetizable material

11. Magnetic Disks
Seek Time: Time to move the R/W head to the desired track.
Latency or Rotational Delay Time: Time to rotate the disk to the desired sector of a track.
Average Latency Time?
Transfer Rate: Rate at which data to be written/read. Transfer rate = n x r /60 where n is the # of bytes per track and r is the revolution per second.
Disk Formatting: Formatting prepares a disk to be used by different disk drives. Formatting creates file allocation table (FAT) that specifies the track and sector of the data items.
Important: Magnetic Disks are direct or random access device because data items can be accessed by specifying its address.
Disk drives with interchangeable disks.
Disk drives with fixed disks.
Disk Controller: Controls the movement of R/W heads, and disk rotation.

12. Disk (Portable/Fixed)
Magnetic Disk Type
Magnetic Disk
Floppy
Disk (1.4 MB)
Hard
Disk
Zip Bernoulli
Disk (Portable/Fixed)
Disk
Packs
WinchesterDisk

13. Advantages & Limitations
Direct Access.
Simultaneous sharing.
On-line/Off-line access.
Unlimited disk may be added.
Low cost.
Portable
Fast
Limitations
Inefficient for sequential data processing.
Sharing make data unsecured
Disk failure.
Cost of magnetic tape is lower
Must be operated in dustless environment

14. Uses of Magnetic Drives
Random access applications
Shared on-line secondary storage.
Data backup.
Data archiving
Data and software transportation.
Software distribution.

15. OPTICAL DISK
In the optic readable CD-ROM, the data storage consists of millions of indentations burnt into light reflecting silver surface. The burnt dents reflect less light than the shiny surface.

16. Tracks
The CD-ROM has only one track, a spiral winding its way from the center to the outer edge. The spiral track is ideal for reading large block of serial data.

17. Access MEchanism
A weak laser beam is sent to the disk through a two-way mirror and the sensor registers the difference in light reflection from the burnt and shiny areas as zeros and ones.
Access time: millisecond.
CD-ROM (Compact disk read only memory).
WORM (Write once read memory)
R/W CD (Read/Write compact disk)

18. Advantages & Limitations
Low cost
Ideal for reading large volumes of data.
No mechanical R/W heads.
Long life data storage.
Easy to handle, store and port.
Limitations
Slower than magnetic disk.
Complicated drive than magnetic disk.
Uses of optical disk
Distribution of large amount of data and Mulltimedia.

19. Mass Storage Disk Array: It uses a set of magnetic disks.
Automated tape library: Uses a set of magnetic tapes.
CD-ROM jukebox: Uses a set of CDROM

20. Memory Hierarchy Cache Memory Main Memory Hard Disk
Smaller Capacity, faster access time and higher cost
Larger Capacity, slower access time and lower cost
Main Memory
Hard Disk
Magnetic tape, Floppy, …
Mass Storage
Memory Hierarchy