ITP 101 Introduction to Information

Technology Storage

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Overview •  Secondary Storage

– Magnetic Media •  Floppy Disks •  Hard Disks

–  Files & fragmentation – RAID

– Optical Storage – Flash Memory

•  Cloud Storage

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•  Why do we need to know this stuff in detail? – To show the computer support guy you know

what you’re talking about J – Databases – Computer Forensics – Recovering your deleted files!

Storage

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Floppy Disk •  Data storage medium

–  composed of a disk of thin, flexible ("floppy") magnetic storage medium –  sealed in a square or rectangular plastic carrier lined with fabric that

removes dust particles •  Read and written by a floppy disk drive (FDD) •  Invented by IBM •  3 sizes – 8", 5 ¼", and 3 ½" •  Used from the mid-1970s to

the late 1990s •  8-track of removable media •  By 1996, there were an estimated five billion floppy disks in use

•  Max storage for 3 ½" floppy disk in 1997 was 240 MB

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•  Disk is broken down into Tracks and Sectors –  Track – Concentric ring around the disk –  Sector – Pie-shaped wedge section of the disk

•  It is the smallest unit that can be obtained at once from a disk •  Cannot retrieve one byte at a type, must retrieve one sector

at a time

Floppy Disk – Storing Data

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Floppy Disk – Reading & Writing •  A small motor in the drive rotates the diskette at a regulated speed •  A second motor-operated mechanism moves the magnetic read–

write head along the surface of the disk •  Both read and write operations require physically contacting the

read–write head to the disk media, an action accomplished by a "disk load" solenoid.

•  To write data: –  Current is sent through a coil in the head –  The magnetic field of the coil magnetizes spots on the disk as it rotates;

the change in magnetization encodes the digital data. •  To read data:

–  The tiny voltages induced in the head coil by the magnetization on the disk are detected, amplified by the disk drive electronics, and sent to the Floppy disk controller

–  The controller separates the data from the stream of pulses coming from the drive, decodes the data, tests for errors, and sends the data on to the host computer system.

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Geek Joke

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•  Where most of your data is saved on your computer

•  Internal persistent storage device •  Invented in the 1950s •  A typical desktop machine will have a hard disk

with a capacity of between 40 and 200 gigabytes •  Data is stored onto the disk in the form of files

–  A file is simply a named collection of bytes •  Contains 3-5 magnetized platters spinning 5400+

revolutions per minute (RPM) •  98% of magnetic hard disk market dominated by

Western Digital and Seagate

Hard Disks

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Hard Disk – Inside http://www.pantherproducts.co.uk/Articles/What_is/What_is_Hard_Disk.shtml

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•  Logical breakdown of a hard disk – Tracks

•  Like tracks on an LP or a CD •  Rings that go completely around the center of the

platter – Sectors

•  Pie-shaped wedges of tracks •  Multiple sectors = 1 track •  512 bytes for magnetic media, 2048 bytes for optical

media – Cylinders

•  All tracks that line up on parallel platters •  Multiple tracks = 1 cylinder

Hard Drive Logically

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Tracks, Cylinders, and Sectors

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•  Why does my paper take up 4 KB of hard disk space when it is only a page long? –  Windows file systems break down the hard disk into

clusters. Each file can use one or more clusters. •  1 sector = 512 bytes •  1 cluster = 8 sectors (default)

= 4096 bytes = 4 KB –  The smallest a file can be (typically) is 4 KB –  All files have sized in multiples of 4 KB

•  File fragmentation –  Clusters do not need to be consecutive –  “Defragmenting” the hard disk will attempt

to place all clusters in consecutive order for files

Files and File Fragmentation

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•  Probably didn’t – Possible to recover evidence and files off of

people’s systems that have “crashed” •  Read/write heads are extremely close to the

platters –  “Liquid ball bearings” –  If the head makes contact with the platter, called

a “head crash”, and it will destroy your data •  Possible to take the platters out of the drive

and place them in a new drive – Needs a clean room

My hard disk crashed!

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•  Redundant Array of Independent Disks –  Nowadays, it is called a “Redundant Array of Inexpensive Disks”

•  Takes 2 or more physical hard disks and makes it look like one hard disk to the computer and user

•  Umbrella term for computer data storage schemes that can divide and replicate data among multiple disk drives

•  The various designs of RAID systems involve two key goals: –  Increase data reliability –  Increase input/output performance

•  Advantages: –  Larger capacity and faster access

•  Disadvantage: –  More points of failure

RAID

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RAID 0, RAID 1, RAID 5

•  Many RAID levels employ an error protection scheme called "parity" •  Most use the simple XOR (exclusive or) parity

–  Meaning "one or the other, but not neither or both”

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RAID 0 RAID 1 RAID 5 Description Block-level striping

without parity or mirroring

Mirroring without parity or striping

Block-level striping with distributed parity

Minimum # of disks 2 2 3 Fault tolerance No Yes Yes Speed Increase Yes No Yes Total storage* Two 200GB Drives

= 400 GB Two 200GB Drives = 400 GB

Three 200GB Drives = 600 GB

Total data storage* 400 GB 200 GB 400 GB

RAID 0, RAID 1, RAID 5

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A1 – D3 represent blocks of data Ap – Dp represent parity data

•  Instead of using polarized charge, it uses reflective pits –  “Lands” – flat areas of the

disk –  “Pits” – parts of the disk that

take a different time to reflect the light

•  The time to reflect back to the source determines whether a 1 or a 0 was read

Optical Media

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•  CD-ROM –  Granddaddy of them all –  Developed by Sony and Phillips –  Commercially available since October 1982 –  650 MB, 74 minutes of audio (thanks to Beethoven’s 9th symphony) –  Created for distributing audio

•  DVD –  Digital versatile disc or digital video disc –  Available in US since March 1997 –  4.7 GB for single layer, single sided –  Created for distributing video

•  Blu-Ray –  Created for distributing high-definition video –  Officially released in June 2006 –  25 or 50 GB discs

Optical Media

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Blu-ray Disc, DVD, & CD

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•  Used in USB flash (aka. thumb) drives, digital cameras, solid state drives, and MP3 players

•  Type of EEPROM – electrically erasable programmable read-only memory

•  Uses electrical signals and current to store memory – similar to RAM

•  More reliable than magnetic media •  No moving parts •  Lifetime is an issue •  Flash memory as a replacement for hard drives

–  Used in Apple's MacBook Air, iPhone & iPad •  In 2008, the flash memory industry

includes about US$9.1 billion in production and sales

Flash Memory

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Floppy / Flash Comparison SD memory card •  32 GB •  $20 •  $0.0006 / MB •  $0.63 / GB

Floppy Disk •  1.44 MB •  $0.80 •  $0.55 / MB •  $569 / GB

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Source: Amazon.com (April 2013)

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Cloud Storage •  Instead of data residing on a local storage

device, it is stored online for you in large data centers – Data is typically synced to multiple hard drives

by the storage provider – Data is pushed by the

internet to multiple devices •  Becoming very popular with

enterprises and companies

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Cloud Storage •  Advantages

–  Pricing directly related to the amount stored •  No wasted space

–  Data is synced across multiple devices by the cloud provider

•  Typically no data loss

•  Disadvantages –  You do not control your data –  Security & Privacy Issues

•  Encryption becomes very important –  If the provider is compromised (hacked), then your data is

compromised

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Cloud Storage Providers

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Cloud Storage Pricing •  Dropbox – 2GB Free, $99/yr for 100GB •  iCloud – 5GB Free, $100/yr for 50GB •  SkyDrive – 7GB Free, $50/yr for 100GB •  Google Drive – 5GB Free, $60/yr for 100GB •  500 GB External Hard Drive - $60

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