Storage and Multimedia Part 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. 2

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. 3

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 4

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. 5

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 6

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 7

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 8

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 9

File Organization Three major methods of organizing data files in secondary storage –Sequential –Direct –Indexed 10

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 11

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 12

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 13

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 14

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 15

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 16

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 17

Multimedia Presents information with text, illustrations, photos, narration, music, animation, and film clips Not practical until the advent of the optical disk 18

Multimedia 19

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 20

Applications Education –Go on virtual tours –Study musical scores –Study a foreign language –Play educational games 21

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 22