Storage and Multimedia

Storage Devices Used to store data and programs permanently on storage media Computer hardware component that writes and reads data to and from storage media Writing data means recording data from memory to a storage medium Reading or retrieving data means transferring data from storage medium into the computer memory for use by the operating system or application program

Storage Devices Speed of the storage device and memory is defined by access time Access time of storage device is measured as the amount of time that the storage device takes to locate and retrieve a specific data on the storage medium Access time of storage device is slower than the access time of memory

Storage Devices Floppy Disk Zip Disk Hard Disk Magnetic Tape CDs and DVDs

Types of Storage Devices Magnetic Storage Devices Optical Storage Devices Mobile Storage Devices

Magnetic Storage Devices Diskette drives, tape drives and hard disk drives are examples of magnetic storage devices Used to write and read data to and from the storage devices The surface of the diskettes, tapes and hard disks are coated with magnetic material such as iron oxide or ferrous oxide, which can be magnetized

Magnetic Storage Devices The surfaces of disks and magnetic tapes are coated with million of tiny iron particles so that data can be stored on them Each of these particles can act as magnet The write/read heads of disk drives or tape drives contain electromagnets that generate magnetic fields in the iron on the storage medium as the head passes over the disk or tape

Magnetic Storage Devices In reading process, no current is flowing through the electromagnetic and read/write heads have no magnetic field Because the storage medium has a magnetic field but the head does not The disk or tape drive senses the direction of the flow as the disk or tape passes by the head Data is sent from the read/write head into memory in the form of electric pulses

Magnetic Disk Commonly used in computers as secondary storage A magnetic disk is a circular metal or plastic disk coated on both sides with magnetic recording material Data on magnetic disk is recorded as magnetic field Data is stored on both sides of the disk, and each side has its own read/write head

Types of Magnetic Disk Floppy Disk or Interchangeable Disk Hard Disk or Fixed Disk

Organizing Data on Magnetic Disk Before to store the data on the magnetic disk, it is prepare through operating system The disk surface is magnetically mapped The process of mapping the surface of disk is called formatting or initializing http://www.karbosguide.com/books/pcarchitecture/chapter44.htm

Disk Areas Windows operating system divides the disk into four areas: Boot Master Record File Allocation Table (FAT) Root Folder Data Area

Floppy Disk Magnetic storage media Plastic disk coated on both side with magnetic recording material Size of the disk refers to the diameter of disk and not refers to the storage capacity High density disks are smaller in size but larger in storage capacity

Floppy Disk http://dl.uncw.edu/digilib/chemistry/computer%20applications/hardware/chpt01c/chpt01c.htm

Floppy Disk Drive Hardware component used to write and read data to and from the floppy disk It includes a motor that rotates the disk on the spindle It also contains write/read head that writes and reads the data to and from the disk when disk rotates Floppy disk rotates 300 revolutions per minute

Zip Disk Portable magnetic media Storage capacity is about from 100MB to 800MB Storage capacity is 100 times greater than floppy disk More reliable than floppy disk https://commons.wikimedia.org/wiki/File:PIC_0856_SuperDisk.JPG

Hard Disk Most commonly used storage device in personal computer and laptop computer Most application program and operating system require hard disk for installation and operation Also referred to as fixed disk

Hard Disk http://www.seltel.cz/?page_id=5596

Magnetic Tape Plastic ribbon with width 0.25 inch to 1 inch and one side coated with magnetic recording material which can be magnetized Divided into vertical columns called frames and each frame is further divided into horizontal rows called tracks Magnetic tape drive is a device that writes/reads data from a magnetic tape

References Introduction to Information Technology by Riaz Shahid, CM Aslam and Safia Iftikhar The Concepts of Information Technology by Imran Saeed, Ahsan Raza, Tariq Mehmood and Zafar Hussain