1 Secondary Storage Chapter 05. 2 Chapter Objectives Properties of Secondary Storage Discuss various mediums of Secondary Storage Magnetic Drives Optical.

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Secondary Storage

Chapter 05

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Chapter Objectives

Properties of Secondary Storage

Discuss various mediums of Secondary Storage Magnetic Drives Optical Drives Magnetic Tape Systems USB Flash Drive

Data Organization

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Properties

Physical Parts

Nonvolatility Property

Removable versus Nonremovable

Media

Accessing Data

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Physical PartsA peripheral storage device can be internal or external.

Internal devices - such as diskette, hard disk, and optical disk drives - typically come installed and configured within the system.

External devices - are stand alone pieces of hardware that connect via cables to ports on the system unit.

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Nonvolatility Property

Secondary storage media are

nonvolatile

Nonvolatile storage - Storage that retains

its contents when power is shut off

Volatile storage - Storage that loses its

contents when power is shut off

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Removable versus Nonremovable Media

Removable Media - Diskettes, CD-ROMs, and magnetic-tape cartridgesNonremovable Media (fixed media) - hard disk systemsRemovable media offer unlimited storage capacity, transportability, backup and security.Nonremovable media offer higher speed and better reliability at lower cost.

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Accessing Data

The process of retrieving data and programs

in storage is called access.

Two methods of data access

Sequential access… Tapes etc

Direct access….. Computer hard disks, CDs etc

Computer system disks allow both sequential and direct access to data

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Magnetic Disk Systems

Secondary Storage

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Magnetic Disk Systems

Most widely used Secondary Storage media

that record data through magnetic spots on

platters made of rigid metal or flexible

plastic for e.g. diskettes (Floppy Disks),

Hard Disks

Provide speedy access

Are relatively low in cost

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DiskettesA low capacity, removable disk made of a tough, flexible plastic and coated with a magnetizable substance.They are used for Doing small amounts of

backup Sending programs and files to

others through mail Storing rarely used files so

they won’t crowd your hard disk

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Diskette Size Sharing data among all the computer

you use.

3.5” in diameter, circular shaped storage medium contained in a square, plastic case that can fit into a shirt pocket.

Sizes 720 KB 1.44 MB

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Physical PropertiesHard Plastic CoverWrite Protect SquareLabelHigh Density Indicator HoleMetal HubSpring Loaded ShutterLinersThe Plastic Surface coated with magnetizable substance

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Zip DriveA Zip drive is a small, portable disk drive used primarily for backing up and archiving personal computer files.

The trademarked Zip drive was developed and is sold by Iomega Corporation.

Zip drives and disks come in two sizes. The 100 megabyte size and 250 megabyte drive and disk.

The Iomega Zip drive comes with a software utility that lets you copy the entire contents of your hard drive to one or more Zip disks.

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Hard DisksA hard disk consists of one or more rigid metal platters mounted onto a shaft and sealed along with an access mechanism inside a case.

The terms hard disk and hard drive are same.

Floppy disk spin at 300 rpm, hard disk spin anywhere from 3600 to 9600 rpm.

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Hard Disks100 GB = 70000 3.5 inch floppy disks.

Constantly rotating - Eliminates waiting time for the drive to come up to the correct speed, whereas diskette does not start spinning until accessed.

Access mechanism - A mechanical device in a disk drive that positions the read/write heads on the proper tracks.

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Disk Access Time

Disk access time - The time taken to

locate and read (or position and write)

data on a disk device.

Disk access time = seek time + rotational

delay + data movement time

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Disk CacheDisk cache is a special area of RAM used to store small amount of disk data. Such data can later be accessed thousands of times faster than they could from disk.Whenever a user requests data, the computer checks first to see if they are in cache. If they aren’t, they are pulled from the disk, and again, cache is rewritten with neighboring disk data.

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Disk Standards

IDE – Integrated Drive Electronics

EIDE - Enhanced integrated drive electronics

(less expensive and easy to configure)

SCSI - Small Computer System Interface

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IDEIDE (Integrated Drive Electronics) is a standard electronic interface used between a computer motherboard's data paths or bus and the computer's disk storage devices. The IDE interface is based on the IBM PC Industry Standard Architecture (ISA) 16-bit bus standard, but it is also used in computers that use other bus standards. Most computers sold today use an enhanced version of IDE called Enhanced Integrated Drive Electronics (EIDE). In today's computers, the IDE controller is often built into the motherboard.

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EIDEEnhanced (sometimes "Expanded") IDE is a standard electronic interface between your computer and its mass storage drives.EIDE's enhancements to Integrated Drive Electronics (IDE) make it possible to address a hard disk larger than 528 Mbytes.When updating your computer with a larger hard drive (or other drives), an EIDE "controller" can be added to your computer in one of its card slot.

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SCSISCSI that allow personal computers to communicate with peripheral hardware such as disk drives, tape drives, CD-ROM drives, printers, and scanners faster and more flexibly than previous interfaces. Developed at Apple Computer and still used in the Macintosh, the present set of SCSIs are parallel interfaces. In addition to faster data rates, SCSI is more flexible than earlier parallel data transfer interfaces. The latest SCSI standard, Ultra-2 SCSI for a 16-bit bus can transfer data at up to 80 megabytes per second (MBps). SCSI allows up to 7 or 15 devices (depending on the bus width) to be connected to a single SCSI port in daisy-chain fashion.

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Partitioning

Division of hard disk into separate areas.

Each partition can be treated as

independent disk drive.

Partitioning the hard drive enables

installation of different operating

system for e.g. Windows 98 and UNIX.

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RAIDRedundant arrays of inexpensive disks.

This process hooks up several arrays of relatively small disks in parallel to do the job of the larger disk.

The disks are separated from the system unit in a cabinet that, is often referred to as the disk subsystem.

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RAIDThe subsystem is set up to record redundant copies of information so that, in the event of system crash, the redundant data can be used to reconstruct the lost data.

Duplicating the entire contents of a disk to another disk is sometimes described as disk mirroring.

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Optical Disk Systems

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Optical Disk Systems

Optical Disk – A disk read by reflecting

pulses of laser beams.

Types of Optical Disks

CDs

DVDs

HD

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Optical DiskGeneral characteristics

Uses “single track spiral” concept

Uses laser beam to read and write data

Read/write process from the center of the disc outwards

Direct/random data access

Requires proper care

Advantages: higher capacity, more reliable and durable than floppy disks

Disadvantages: sensitive

Basic types: CD & DVD

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Compact Disk (CD)A rigid plastic disk that stores a large amount of data through the use of laser. The underside of the plastic CD disk is coated with a very thin layer of aluminum that reflects light.Data is written to the CD by burning microscopic pits into the reflective surface of the disk with a powerful laser. The pits represent a value of 0 and flat spots, called land, representing a value of 1.

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Compact Disk (CD)Data is read from a CD-ROM with a low power laser.The pits does not reflect the laser light.The land portions of the disk reflect the laser light efficiently to the photodetector.The photodetector then converts these light and dark spots to electrical impulses corresponding to 1s and 0s.

Diagram of CD Pit layout.

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Compact Disk (CD)The most common format of CD-ROM holds approximately 630 megabytes.Approximately 269,000 pages of text, or more than 7,500 photos or graphics.A single-speed CD-ROM player reads 150,000 bytes of data per second.A typical CD-ROM takes about a third of a second to access data, as compared to a typical hard drive, which takes about 10 milliseconds (thousandths of a second) to access data.

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CD - ROMCD-ROM (Compact Disc, read-only-memory)Designed to store computer data in the form of text and graphics, as well as hi-fi stereo sound.A standard CD is 120 mm (4.75 inches) in diameter and 1.2 mm (0.05 inches) thick and is composed of a polycarbonate plastic substrate (underlayer - this is the main body of the disc), one or more thin reflective metal (usually aluminum) layers, and a lacquer coating.

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Different types of CD-ROMCD-R WORM (Write-Once-Read-Many.)CD-RW (for compact disc, rewriteable) is a compact disc (CD) format that allows repeated recording on a disc.VCD is a compact disk format specifically designed to hold MPEG-1 video data and to include interactive capabilities.

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Digital Versatile Disk (DVD)

The (DVD) holds 4.7 gigabyte of information on one of its two sides, or enough for a 133-minute movie.With two layers on each of its two sides, it will hold up to 17 gigabytes of video, audio, or other information.DVD-ROMs have seven times the storage capacity of CD-ROMs.DVD-ROM drives have a base speed of 1.32 megabytes/second.DVD-ROM drives are backward compatible, and can read CD-ROMs.

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DVD TypesDVD-R: Recordable (DVD-R) is a type of write once, read many (WORM) DVDDVD-RW: DVD format that allows the user to record and erase multiple times on a single DVD disk.

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DVD - Layers

Format Capacity Movie Length

Single Sided/Single Layer 4.38 GB 2 hours

Single Sided/Double Layer 7.95 GB 4 hours

Double Sided/Single Layer 8.75 GB 4.5 hours

Double Sided/Double Layer 15.9 GB Over 8 hours

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DVD - Layers

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HD-ROM(High Density-Read-Only-Memory)

HD-ROM is a high capacity storage technology developed at Norsam Technologies, in conjunction with an IBM research group.HD-ROM technology can be used to write data on different types of media, such as metal or other durable materials, to create virtually indestructible storage.HD-ROM's particle beam, at a size of 50 nanometers, enables a storage capacity of 165 gigabytes on disks the same size as a CD or DVD.

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Magnetic Tape Systems

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Magnetic Tape SystemsMagnetic tape is made of Mylar, a type of strong plastic, into which metallic particles have been embedded. A read/write head identical to those used for audio tape reads and writes binary information to the tape.

Reel-to-reel magnetic tape is used to store information for large mainframe or supercomputers.

High-density cassette tapes are used to store information for personal computers and mainframes.

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Magnetic Tape SystemsAdvantages It is able to hold enormous amounts of data; for

this reason it is used to store information on the largest computer systems.

It is less expensive than magnetic disk and optical disk technology.

Disadvantages Slow data access time compared to other

media. Sequential access to information.

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USB Flash Drive

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USB Flash Drive

A memory card that plugs into the computer's USB portSmall enough to hook onto a keychainSoftware drivers are not required for the newer operating systemsIt comes with a removable cap to protect type-a male USB connector and a hole or loop through which a string or wire loop can be attached Also known as:

"flash drive," "pen drive," "keychain drive," "key drive," "USB key," "USB stick" "memory key,"

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Flash MemoryFlash memory is non-volatile computer memory that can be electrically erased and reprogrammedIt is a technology that is primarily used in USB Flash DrivesFlash Memory has a faster access time although not as fast as volatile DRAM memory used for main memory in PCsIt is a specific type of EEPROM (Electrically Erasable Programmable Read-Only Memory) that is erased and programmed in large blocks. Early flash the entire chip had to be erased at once but latest flash can be erased in blocks.

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CapacityCommon flash memory parts range widely in capacity from kilobits to several gigabits eachMultiple chips are often arrayed to achieve higher capacities for use in devices such as the iPod nano, video & digital camera

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Data Organization

Secondary Storage

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Difference b/w Data Organization & Data Access

Data access - The process of fetching data

either sequentially or directly from a

storage device.

Data organization - The process of setting up

data so that they may subsequently be

accessed in some desired way.

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Data Organization

Data is organized in three major ways

Sequential Organization

Indexed Organization

Direct Organization

Key field - A field that helps identify a record.

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Sequential Organization

Arranging data on a physical medium in

either ascending or descending order by

the contents of some key field.

It often suits the data requirements of

batch processing operations by ordering

records with respect to a key field.

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Indexed Organization

A method of organizing data on a direct

access storage medium so that they can

be accessed directly (through an index) or

sequentially.

This type of organization requires disk

storage, because tape cannot provide

direct access.

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Direct Organization

A method of arranging data on a

storage device so they can be accessed

directly (randomly).

Both indexed and direct organization

support the data needs of transaction

processing and real-time processing.

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Data Access (Processing)

There are three types of data processing

Batch processing

On-line (Transaction) processing

Real-time processing