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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
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