COMPUTER SCIENCEData Representation and Machine ConceptsSection 1.3

Instructor: Lin Chen

August 2013

1.3 Mass Storage

1 Data Storage

Magnetic Systems

Optical Systems

Flash Drives

File Storage and Retrieval

Pearson Custom: Computer Science, Data Representation and Machine Concepts

Introduction

1.3 Mass Storage

Mass StorageAdditional memory, secondary storageIncluding magnetic disks, CDs, DVDs, magnetic tapes,and flash drives

AdvantagesLess volatilityLarge storage capacityiesLow costThe ability to be removed

Introduction

1.3 Mass Storage

Terms

On-LineThe device or information is connected and readily available to the machine without human intervention

Off-LineHuman intervention is required before the device or information can be accessed by the machine

Magnetic System

1.3 Mass Storage

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

http://en.wikipedia.org/wiki/Hard_disk_drive#Magnetic_recording

Magnetic System

1.3 Mass Storage

Hard Drive

http://www.computer-hardware-explained.com/computer-hard-drive.html

Magnetic System

1.3 Mass Storage

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

http://users.dickinson.edu/~braught/courses/cs354s10/topics/slides/06-filesystems.pdf

Magnetic System

1.3 Mass Storage

Hard Drive Information on each sector is a continuousString of bits

All sector contain the same number of bits(512 Bytes to a few KB)

The tracks near the outer edge can containsmore sectors due to the longer perimeterSpindle

http://users.dickinson.edu/~braught/courses/cs354s10/topics/slides/06-filesystems.pdf

Magnetic System

1.3 Mass Storage

Hard Drive

FormattingProcedure initializing the location of tracks and sectors

Low-level formattingEstablish the tracks and sectors on the disk, the starting end

ending points of each sector are written onto the platter

High-level formattingWrite the file-storage structures, prepares the drive to hold files

Magnetic System

1.3 Mass Storage

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

Magnetic System

1.3 Mass Storage

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?

Magnetic System

1.3 Mass Storage

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?

Magnetic System

1.3 Mass Storage

Hard Drive

Suppose that a disk drive has 5000 cylinders, numbered 0 to 4999. Thedrive is currently serving a request at cylinder 143, and the previousrequest was at cylinder 125. The queue of pending requests, in FIFOorder, is

86, 1470, 913, 1774, 948, 1509, 1022, 1750, 130Starting from the current head position, what is the total distance (incylinders) that the disk arm moves to satisfy all the pending requests?

http://web.cs.du.edu/~dconnors/courses/comp3361/assignments/ch12.pdf

Magnetic System

1.3 Mass Storage

Floppy Disk

http://en.wikipedia.org/wiki/File:Floppy_disk_2009_G1.jpg

Magnetic System

1.3 Mass Storage

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

Magnetic System

1.3 Mass Storage

Magnetic Tape

Access data by a tape drive, which canread, 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

http://en.wikipedia.org/wiki/File:Ibm-729v.jpg

Optical Systems

1.3 Mass Storage

Compact Disk

CD-DA (Compact Disk-Digital Audio)store and play back sound recording

CD-ROM (CD Read-Only Memory)store data

CD-Rwrite-once audio

CD-RWrewritable media

VCDvideo compact disc

DVDdigital optical disc storage

Optical Systems

1.3 Mass Storage

Compact Disk

http://www.clker.com/clipart-3223.html

Optical Systems

1.3 Mass Storage

Compact Disk

12 centimeters in diameter

Single track that spirals around the CD

The track is divided into sectors, each sector contains 2KB data

http://electronics.howstuffworks.com/cd2.htm

Optical Systems

1.3 Mass Storage

Compact Disk

A. A polycarbonate disc layer has the data encoded by using bumps

B. A shiny layer reflects the laserC. A layer of lacquer protects the shinyD. Artwork is screen printed on the top

of discE. A laser bean reads the CD

http://en.wikipedia.org/wiki/File:CD_layers.svg

Optical Systems

1.3 Mass Storage

Compact Disk

Data is represented as tiny indentations known as “pits”

http://en.wikipedia.org/wiki/File:Comparison_CD_DVD_HDDVD_BD.svg

http://www.clir.org/pubs/reports/pub121/sec3.html

DVD

Flash Drives

1.3 Mass Storage

http://tohii.blog.china.com/201203/9424017.html

http://data-recovery-weekly.blogspot.com/2010/06/fake-flash-drive.html

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)

File Storage and Retrieval

1.3 Mass Storage

Physical RecordA block of data conforming to the specific characteristics

of a determined size

Logical RecordNaturally occurring blocks of data

File Storage and Retrieval

1.3 Mass Storage

On Hard Disk

Observed in system

File1 File2

File1 File2

Physical Record

Logical Record

File Storage and Retrieval

1.3 Mass Storage

On Hard Disk

Observed in system

Piece 1 Piece 2

File

Physical Record

Logical Record