1. Computer SCIENCE Data Representation and Machine Concepts Section 1.3
Instructor: Lin Chen
August 2013

2. 1 Data Storage 1.3 Mass Storage Magnetic Systems Optical Systems
Flash Drives
File Storage and Retrieval
Pearson Custom: Computer Science, Data Representation and Machine Concepts

3. 1.3 Mass Storage Introduction Mass Storage
Additional memory, secondary storage
Including magnetic disks, CDs, DVDs, magnetic tapes,
and flash drives
Advantages
Less volatility
Large storage capacityies
Low cost
The ability to be removed

4. 1.3 Mass Storage Introduction Terms On-Line
The device or information is connected and readily available to
the machine without human intervention
Off-Line
Human intervention is required before the device or information
can be accessed by the machine

5. 1.3 Mass Storage Magnetic System
Uses a thin spinning disk with magnetic coating to hold data
Hard drive
Floppy drive
Tape
Sequential changes in the direction of magnetization represent binary data 0 and 1

6. 1.3 Mass Storage Magnetic System Hard Drive

7. 1.3 Mass Storage Magnetic System Hard Drive
Several platters are fixed on same spindle
Track, each circle lane
Sector, each track is divided into small arcs
Read/Write head are placed above and
below each disk
Spindle

8. 1.3 Mass Storage Magnetic System Hard Drive
Information on each sector is a continuous
String of bits
All sector contain the same number of bits
(512 Bytes to a few KB)
The tracks near the outer edge can contains
more sectors due to the longer perimeter
Spindle

9. 1.3 Mass Storage Magnetic System Hard Drive Formatting
Procedure initializing the location of tracks and sectors
Low-level formatting
Establish the tracks and sectors on the disk, the starting end ending points of each sector are written onto the platter
High-level formatting
Write the file-storage structures, prepares the drive to hold files

10. 1.3 Mass Storage Magnetic System Hard Drive Access time
Seek time (~ 4ms)
the time required to move the read/write heads from on track to another
Rotational latency (~ 5ms)
half the time required for the disk to make a complete rotation
Transfer time (MB per second, fastest)
the rate at which data can be transferred to or from the disk

11. 1.3 Mass Storage Magnetic System Hard Drive Access time
Seek time (~ 4ms)
the time required to move the read/write heads from on track to another
Rotational latency (~ 5ms)
half the time required for the disk to make a complete rotation
Transfer time (MB per second, fastest)
the rate at which data can be transferred to or from the disk
Why?

12. 1.3 Mass Storage Magnetic System Hard Drive
Calculate the hard drive size:
A hard drive has 10 platters, each platter has 200 tracks, each tracks has same number of sectors, each sectors can save 512 bytes, what is the size of this hard drive?

13. 1.3 Mass Storage Magnetic System Hard Drive
Suppose that a disk drive has 5000 cylinders, numbered 0 to The
drive is currently serving a request at cylinder 143, and the previous
request was at cylinder 125. The queue of pending requests, in FIFO
order, is
86, 1470, 913, 1774, 948, 1509, 1022, 1750, 130
Starting from the current head position, what is the total distance (in
cylinders) that the disk arm moves to satisfy all the pending requests?

14. 1.3 Mass Storage Magnetic System Floppy Disk

15. 1.3 Mass Storage Magnetic System Floppy Disk Single plastic disk
3 1/2 floppy disk has capacity of 1.44 MB
Off-line device
Question:
how many tracks in above floppy disk, suppose each sector contains 512 bytes

16. 1.3 Mass Storage Magnetic System Magnetic Tape
Access data by a tape drive, which can
read, write, and rewind the tape
Size can be several GB
Disadvantage:
Reading between two different positions on a tape is time-consuming
Off-line device

17. 1.3 Mass Storage Optical Systems Compact Disk
CD-DA (Compact Disk-Digital Audio)
store and play back sound recording
CD-ROM (CD Read-Only Memory)
store data
CD-R
write-once audio
CD-RW
rewritable media
VCD
video compact disc
DVD
digital optical disc storage

18. 1.3 Mass Storage Optical Systems Compact Disk

19. 1.3 Mass Storage Optical Systems Compact Disk
12 centimeters in diameter
Single track that spirals around the CD
The track is divided into sectors, each sector contains 2KB data

20. 1.3 Mass Storage Optical Systems Compact Disk
A polycarbonate disc layer has the data encoded by using bumps
A shiny layer reflects the laser
A layer of lacquer protects the shiny
Artwork is screen printed on the top of disc
A laser bean reads the CD

21. 1.3 Mass Storage Optical Systems Compact Disk
Data is represented as tiny indentations known as “pits”
DVD

22. 1.3 Mass Storage Flash Drives
Chambers of silicon dioxide capture the electrons to represent the binary number
Hold data for many years
Too many erasing could damages the silicon dioxide chamber
Not sensitive to physical shock (portable)

23. File Storage and Retrieval
1.3 Mass Storage
File Storage and Retrieval
Physical Record
A block of data conforming to the specific characteristics of a determined size
Logical Record
Naturally occurring blocks of data

24. File Storage and Retrieval
1.3 Mass Storage
File Storage and Retrieval
File1
File2
Physical Record
On Hard Disk
File1
File2
Observed in system
Logical Record

25. File Storage and Retrieval
1.3 Mass Storage
File Storage and Retrieval
Piece 1
Piece 2
Physical Record
On Hard Disk
Observed in system
Logical Record
File