Storage and MultimediaPart II

Bayram Güzer

Magnetic Tape Storage

• It is similar to tape used in music cassettes– Plastic tape with a magnetic coating.

• Data is stored as extremely small magnetic spots.

• Types of tapes;– ½ inch wide tape in reels– ¼ inch wide tape in cartridges and

cassettes– Tapes that look like ordinary music

cassettes but are designed to store data.

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Magnetic Tape Storage

• Amount of data in tapes are expressed in terms of density– Number of bytes per inch (bpi) stored

on tape– Number of characters per inch (cpi)

stored on tape• Data on the tape is accessed

sequentially while on the disk it is accessed directly.

• Used primarily for backup of data stored on disk systems as inexpensive backup medium.

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Backup Systems

• It is very important to have copies of important data stored away from the computer– Disks rarely fail

– Software installation can cause computer to crash

– Users make mistakes entering data

• Tape is ideal backup medium– Can copy entire hard disk to single tape in minutes

– Backup can be scheduled when you are not going to use the system

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Organizing and Accessing Stored Data

• Organizations that store data usually need a lot of data on many subjects– Charity organization would need detailed

information about donors, names and schedules of volunteers

– A factory would need to keep track of inventory– A school would need detailed personal and

academic records of students

• All this data is stored in a predefined organization.

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Organizing and Accessing Stored Data

• Character– A letter, digit, or special

character• Field

– A set of related characters

– Describes one characteristic of a person, place, or thing

• For a university, a student’s first name would be stored in a field

– Key field - a unique identifier for a record

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Organizing and Accessing Stored Data

• Record– A collection of related

fields• For the university, all of

the fields for one student constitute one record

• File– A collection of related

records• For university, all the

student records compose a file

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Organizing and Accessing Stored Data

• Database– A collection of related

files stored with minimum redundancy (duplication)

• For university, student file, alumni file, faculty/staff file, courses file, financial file, etc. would make up a database

– Organized to make retrieving data easier

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File Plan Overview

• Must devise a plan for placing data on a storage unit

• Key factors– Whether users must access data directly

(immediately)– How data must be organized on disk– Type of processing that will take place

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File Organization

• Three major methods of organizing data files in secondary storage– Sequential– Direct– Indexed

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Sequential File Organization

• Records are stored in order according to a key field– If a particular record is desired, all prior records

must be read first– To update a record, a new sequential file must

be created, with changed and unchanged records

• Tape storage uses sequential organization

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Direct File Organization

• Also called random access

• Go directly to desired record by using a key– Computer does not have to

read all prior records

– Hashing algorithm used to determine address of given key

• Requires disk storage

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Hashing Algorithm

• Applies mathematical formula to key to determine disk address of given record– Collision occurs when hashing algorithm

produces same disk address for two different keys

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Indexed File Organization

• Combines elements of sequential and direct methods– Records stored sequentially, but file also

contains an index– Index stored sequentially, contains record key– Data accessed by record key

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Processing Stored Data• Transactions processed to update a master file

– Transactions - a business event such as a sale– Master file - data that is updated when a

transaction occurs, such as a sales file or inventory file

• Two main methods of processing data– Batch processing– Transaction processing

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Batch Processing

• Transactions collected into groups or batches– Batch processed and

master file updated in a regular basis

• Very efficient use of computer resources

• Master file current only immediately after processing

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Transaction Processing

• Processing transactions as they occur– Also called real-time

processing and online processing

– Terminals must be connected directly to the computer

• Offers immediate updating of master file

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Multimedia

• Presents information with text, illustrations, photos, narration, music, animation, and film clips

• Not practical until the advent of the optical disk

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Multimedia

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Requirements

• CD-ROM or DVD-ROM drive

• Sound card or sound chip

• Speakers– For high-quality sound, get good speakers and

powered subwoofer

• Equipped to handle the appropriate format

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Applications

• Education– Go on virtual tours– Study musical scores– Study a foreign language– Play educational games

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References

• Capron, H. L. (2000). Computers Tools for an Information Age.(6th ed.). New Jersey, USA: Prentice Hall.

• Multimedia. (2009). Retrieved 27 December 2009 from http://en.wikipedia.org/wiki/Multimedia

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