1. 6 Secondary Storage computing ESSENTIALS    
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2. Competencies computing ESSENTIALS     Different types of media
Floppy disks
Hard disks
Performance enhancements
Optical disks
Specialized media
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computing ESSENTIALS    
Secondary Storage
Stores information
Non-volatile, permanent storage
Characteristics
Media
Capacity
Access time
Secondary storage is – stores programs and data
nonvolatile as opposed to volatile (temporary) storage (RAM) which is lost when power shut off to computer.
Media – actual physical material that hold data
Capacity – amount of data the storage medium can hold
Access time – amount of time to retrieve and write data
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Types of Storage Media
Types widely used today
Floppy disks
Hard disks
Optical disks
Magnetic tape
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Floppy Disks
Portable and removable
Flat circular Mylar media
Magnetic charge on metal oxide film coating
Standard 2HD 1.44 MB
Parts
Tracks
Sectors
Floppy disks are removable storage media. Today’s standard is 2HD (Double sided, double density) 1.44 MB.
Data recorded in rings called called tracks; tracks divided into wedge-shaped sections called sectors
Pieces of floppy flat Mylar rotating within a hard plastic jacket
The bits of data are represented by the presence or absence of magnetic charges
Write-protect notch or window to prevent inadvertent erasure or write-over
Limited capacity today. Many media files far exceed the capacity of standard floppy disks
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6. High Capacity Floppy Disks
computing ESSENTIALS    
High Capacity Floppy Disks
Floppy disk cartridges
Zip Disks
250 MB
SuperDisks
120 MB
HiFD disks
200 MB
Zip disks – usually manufactured by Iomega
100 to 250 MB worth of storage
Requires own drive
Drive can only read/write to Zip disks
Super disks – usually manufactured by Imation
120 MB capacity; popular with notebooks
Drives can also read/write standard 2HD disks
HiDF disks – usually manufactured by Sony Corp
200 MB capacity
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computing ESSENTIALS    
Hard Disks
Metallic disks
Fast retrieval, greater capacity
Read/write heads ride cushion of air ” thick
Three types
Internal hard disk
Hard-disk cartridge
Hard-disk pack
Composed of metallic rather than plastic disks
Fast information storage and retrieval
Read-write head is inch above surface! Any particle of dirt can cause a head crash – scratch across disk
See next slide for good graphic of “space”
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computing ESSENTIALS    
Head crashes occur when the read-write head contacts the disk surface or particle of dirt on the disk surface
The disk and the disk head will likely be damaged causing data to be lost
A smoke particle, human hair or fingerprint could cause a head crash
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computing ESSENTIALS    
Internal Hard Disk
Inside system unit
Non-removable or portable
Great capacity
Over 100 Gigabytes
Fast access speed
Located inside the system unit; also known as fixed disk
Used for storing the operating system, other programs and large data files
One or more metallic platters sealed inside a container
Container holds
Motor for rotating the disks
Access arm and read-write heads
Advantages over floppy disks
56,000 floppies worth of information
Speed (twenty times the speed)
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computing ESSENTIALS    
Hard-disk Cartridges
Portable, removable
Complement internal hard drive
JAZ from Iomega
SPARQ from SyQuest
PC Card Hard Disks
Laptop computers
Capacity limited only by number of cartridges
Used to complement internal hard disk.
Particularly useful for securing data on the drive – can be removed and locked up.
Typical capacity = 2 to 20 GB
Popular vendors: Iomega and SyQuest
PC Card hard disks – hard disk cartridges for notebook and laptop computers.
Typical capacity up to 10 GB
IBM’s Microdrive
Hitachi’s PC Card hard drive
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computing ESSENTIALS    
Hard-disk Packs
Used in mainframes
Removable
Resemble stack of vinyl records
Multiple read/write heads
Massive storage capacity
Fast access time
Common in mainframe systems
Composed of a larger number of platters, resembling a stack of record albums
Most platters offer read-write surfaces on top and bottom
Multiple heads move together, but only one head is active at a time.
Top and bottom outside surfaces of the pack are not used, so a pack of 11 disks gives 20 recording surfaces.
Massive storage capacity
Access time - time between the computer’s request for data from secondary storage and the completion of the data transfer; usually access time is faster with this type of secondary storage
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12. Performance Enhancements
computing ESSENTIALS    
Performance Enhancements
Improving performance of hard disks
Disk caching
Redundant Arrays of Inexpensive Disks (RAID)
File compression and decompression
Disk caching
Uses hardware and software to anticipate data needs
Frequently used data is stored in memory; when needed, the access time is much faster
Redundant arrays of inexpensive disks (RAID)
Groups of low cost hard-disk drives grouped together using networks and special software
Performs as a single large-capacity disk; but faster than a single disk of comparable size
File compression and decompression
Increase storage capacity
Reduce space required for storage; reduce up to ¼ of original size
WinZip and PKZip are well-known programs
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Optical Disks
Very large capacity
Up to 17 gigabytes
Use reflected light projected by a laser
Lands and Pits represent 1’s and 0’s
Formats
Compact Disk (CD)
Digital Versatile Disk (DVD)
DataPlay
uses laser technology.
Compact, high capacity form of permanent storage
Laser beam writes by creating a pattern of pits (holes) and lands (flat areas) to encode data bits
Laser beams reflect off the pits and lands to read the data
CD, DVD, and DataPlay are optical disk formats.
Three basic types of optical discs CD-ROM, CD-R and erasable optical discs, or CD-RW
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Compact Disks
Widely used format today
Can store from 650 MB to 1 GB
Rotational speed = data transfer time
Types of CDs
CD-ROM
CD-R
CD-RW
CD drives come standard on computer systems today.
High capacity of data is stored on them. Typically they are between 650 MB to 1 Gigabyte.
A CD drives rotational speed is important because that determines how fast data can be transferred from the disk.
For example:
A 24X CD drive can transfer 3.6 MB per second
A 32X CD drive can transfer 4.8 MB per second
Data on a CD is written in one continuous stream, similar to a phonograph record groove. However, the data stream begins in the center of the disk and proceeds outwards.
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CD-ROM
Compact Disc-Read Only Memory
Cannot be written to or erased
Similar to commercial music CDs
Used often to distribute large databases or references
Compact disc-read-only memory
Used for distribution of large data such as
Grolier Electronic Encyclopedia - nine million words and 1900 pictures
Large software packages like MS Office
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CD-R & CD-RW
CD-Recordable
Written to once
Custom made music CDs
CD-ReWritable
Erasable CD
Ideal for multimedia presentations
Stands for CD-Recordable
Also known as WORM, or write once, read many
Ideal for use as permanent data archives for essential company information
CD changers or CD jukeboxes can facilitate rapid access to large amounts of information
Also known as rewritable optical discs
Unlike CD-R, these discs can be written on numerous times
Most common technology is magneto-optical (MO) disc drive, combining magnetic and optical technologies
Capacities up to 1,000 megabytes (a gigabyte)
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DVD
Digital Versatile Disk
Rapidly replacing CDs
Higher capacity
17 times the capacity of a CD
4.7 gigabytes to 17 GB per disk
Predicted to replace CD; not quite there – but in great demand and highly used – especially for movies and games
Most computers are beginning to come with DVD drives standard
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computing ESSENTIALS    
DVD Types
DVD types
DVD-ROM
Read only memory
DVD-R
Recordable
DVD-RAM or DVD-RW
Competing rewritable formats
DVD-ROM - provide high quality, movie length videos
4.7 GB storage; seven times a regular CD
DVD-R - consumer recordable version just getting started
4.7 GB storage
DVD-RAM or DVD-RW - rewritable version
2.6 to 5.2 GB storage
Up to 17 gigabytes of capacity, fourteen times CD
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DataPlay
Optical write-once format
Similar to CD-R
Size of a quarter
Used for special applications
Storing digital photographs
Storing music for portable players
Small optical disks with a capacity of about 500 MB.
About the size of a quarter.
Used for small devices such as digital cameras or portable music players.
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20. Other Secondary Storage Types
computing ESSENTIALS    
Other Secondary Storage Types
Complement other secondary storage devices
Specialized device types
Magnetic tape
Internet hard drives
Solid state storage
The basic secondary storage options don’t compete so much as complement each other. Each is suited to their particular tasks.
Magnetic tape, Internet hard drive, and solid state storage further complement the basic types.
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Magnetic Tape
Sequential access
Commonly used for backing-up data
Very large capacity
Types of magnetic tape
Tape cartridges
Magnetic tape reels
Sequential access because they have to be fast forwarded or rewound before a specific location can be reached.
A common sequential access method of
Two forms of tape storage
Magnetic tape cartridges, also called magnetic tape streamers
Magnetic tape reels
Tapes are run on magnetic tape drives or magnetic tape units
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computing ESSENTIALS    
Magnetic Tape Types
Tape cartridges
Backup tape for microcomputer
Capacities range from 120 MB to 5 GB
Digital audio tape (DAT)
Tape reels
Minicomputer and mainframe
1/2 inch wide and 1/2 mile long
Stores 1600 to 6400 cpi
Backup tape cartridge units used with microcomputer systems
Typical capacities range from 120 MB to 5 GB
Advanced forms use digital audio tape (DAT)
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23. Internet Hard Drive and Solid State
computing ESSENTIALS    
Internet Hard Drive and Solid State
Internet hard drive
Free or low-cost storage on the Web
Access information from any location
Access time is greater
Solid-state storage
No moving parts
Flash memory cards
Internet hard drive are located on special secure websites that offer low-cost alternative to local storage.
Advantages:
The data can be accessed from anywhere on the Web.
Low cost compared to buying a high capacity device.
Disadvantages:
Because it must travel through the Web, access time can be slow.
User is dependent on accessibility to the website.
Dependent on the service provider for security.
Solid State Storage
Similar to computer RAM. No moving parts of the media.
Reliable, requires less power
Expensive
Flash memory cards
Used in digital cameras to store images, or in MP3 devices to record music and transfer them to other computer media.
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computing ESSENTIALS    
A Look to the Future
Blue laser light optical devices
Aimed more accurately
Can increase storage capacity to 27 GB per standard optical disk
New players will likely play both
Current DVD and CD players and recorders use red light lasers.
Blue light lasers can be aimed more accurately and compactly.
More compact means more data storage in same amount of space.
Since current players would not be able to read new disk format, new players may incorporate both red and blue lasers.
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