Objectives List the benefits of secondary storage Identify and describe storage media available for personal computers Differentiate among the principal types of secondary storage Discuss the benefits of multimedia Explain how data is organized, accessed, and processed

Optical Technology Optical media technology refers to the optical media devices/optical drives. Optical drives retrieve and/or store data on optical discs like CDs, DVDs, and BDs (Blu-ray discs) which hold much more information than classic portable media options like the floppy disk. Optical are known as CD Drive, DVD drive, BD drive, and disk drive.

Optical Technology They are also very commonly used in computers to read software and multimedia distributed in disc form.

Optical Technology Optical drives—along with flash memory—have mostly displaced floppy disk drives and magnetic tape drives for this purpose because of the low cost of optical media and the near-ubiquity of optical drives in computers and consumer entertainment hardware.flash memory

Secondary Storage Benefits Semi-permanent Non-volatile Reliable Convenient – Locate and access data quickly

Secondary Storage Benefits Compressed storage Diskette – about 500 printed pages Optical disk – about 500 books Economy Savings in physical storage costs Savings in the speed and convenience of filing and retrieving data

History

Types of Storage Magnetic Disk Storage Optical Disks Magneto-optical CD-ROM CD-R CD-RW DVD-ROM Magnetic Tape Storage

Magnetic Disk Storage Data represented as magnetic spots Magnetized spot = 1 Absence of a magnetized spot = 0 Read Converts the magnetized data to electrical impulses Write Converts electrical impulses to magnetized spots on disk

Disk Capacity Size MB older hard disks GB current PC TB coming soon What’s stored? User documents Software Graphic images Audio files Video files

Diskettes Low capacity – small files Portable Flexible Mylar coated with metallic substance Hard plastic jacket for protection 3 ½ inch, 1.44 MB

High-Capacity Portable Disks Larger files Portable High-capacity 120 / 200 MB Can read and write standard diskettes Ex: Superdisk Zip disk 250 MB not compatible with 3 ½ inch diskettes

Data Compression Why use? Squeeze big files onto small disks Speed up data transfer of files Techniques Remove all extra space characters Substitutes a smaller data string for a frequently occurring set of characters Software uses formula to determine how to compress Must be decompressed

Hard Disk Various sizes Portability Generally non-portable Removable hard disks available for PC Rigid platter coated with metallic substance

Disk Pack Several platters Airtight, sealed module Mount disk pack on disk drive

Disk Pack Disk pack has set of access arms Two read / write heads per arm One reads top surface One reads bottom surface Access arms move together as a unit Only one read/write head works at a time

Logical Layout of a Disk Track Concentric circles Passes under read/write head as disk rotates 1.44 MB diskette has 80 tracks on each surface Each track stores the same amount of data

Logical Layout of a Disk Sector Pie-shaped division of track Holds a fixed number of bytes (512 bytes) Cluster –Adjacent sectors treated as a unit of storage –Fixed number (2-8 sectors) –Minimum space allocated to a file

Logical Layout of a Disk Cylinder Same track on each platter Store files across multiple platters Reduces access time

Logical Layout of a Disk Zone Recording Assigns more sectors to tracks in outer zones More sectors = more data storage available

Disk Drive Read / Write Operation Disks rotate Access arm moves read/write head Read / write operation begins and continues until complete Data is transferred to/from memory

Access Time Seek time Head switching Rotational delay Data transfer rate

Optical Disk Greater capacity than other portable media Process Laser writes on metallic material spread over the surface of disk Heat from laser produces pits on disk surface Reading – laser picks up light reflections from the pits Technology ROM WORM

MO Magneto-optical Hybrid High-volume capacity Written multiple times Process Laser melts a microscopic spot Magnet aligns crystals Reading – laser picks up light reflection from crystals

CD-ROM Compact Disk Read-Only Memory High capacity portable Read multiple times Cannot record Capacity – up to 680 MB (450 standard 3 ½ inch diskettes) Used for software distribution

CD-R Compact Disc-Recordable High capacity Portable Write once Read multiple times CD-R drive CD-ROM drive

CR-RW Compact Disk-Rewritable High capacity Portable Read multiple times Record multiple times Some compatibility problems reading CD-RW disks on CD-ROM drives

DVD-ROM Digital Versatile Disk Larger capacity than CD-ROM Standard – Up to 4.7 GB, 7 times more than CD- ROM Double layers – 8.5 GB Double-sided – 17 GB Data is packed more densely Read multiple times, Cannot record Can read CD-ROM disks

DVD-ROM Digital Versatile Disk Benefits Full-length movies Audio quality comparable to audio compact disks High-volume business data Expected to replace CD-ROM in the near future

Data Organizing and Accessing Plan for way data is Received Organized Stored how it will be processed Plan determined by programmer or systems analyst

CD vs. DVD CDDVD Media Diameter  120 mm 120 mm Media Thickness  1.2 mm Track Pitch 1.6  m0.74  m Min Pit/Land Length 0.83  m0.4  m Data Layers11 or 2 Sides11 or 2 Capacity  650 MB 4.38, 7.95, 8.75, 15.9 GB Video Data Rate  1.5 Mbits/s 1-10 Mbits/s Video Compression stdMPEG-1MPEG-2 Video Capacity  1 hour  2 – 8 hours Sound Tracks2-channel MPEG2-channel PCM 5.1-channel AC-3 Optional (up to 8 streams) SubtitlesUp to 32 languages

HD-DVD Standard Definition (SD) Video becomes less acceptable for 36+ inches screen sizes. High Definition TV Images (HDTV) are rated “good” for 60+ inches screen sizes. HD DVD satisfies the public demand for high quality HDTV content arising from increased availability of large screens at affordable prices. HD DVD shares the 12cm diameter and 1.2mm thickness of the current generation of DVD discs, yet is able to deliver eight hours of High Definition video on a dual-layer, single-sided disc. A double-sided HD DVD-R disc can hold up to 30GBytes of data.

Laser Wavelength

Comparison