Welcome to CMPE003 Personal Computers: Hardware and Software Dr. Chane Fullmer Fall 2002 UC Santa Cruz

2 October 16, 2002 Class Information Midterm results due back Friday HW #2 is back – Avg score = 9.93 – Excellent !!

3 October 16, 2002 Assignments Homework #3 – Due October 18 – Design your own Web page – Keep in mind --- The world at large will be able to see your page Dont put private or sensitive information on your Web page. – Details and sample – see class page – If you need help uploading your files to your CATS account, take your disk to section..

Storage and Multimedia: The Facts and More Chapter 6

5 October 16, 2002 Objectives List the benefits of secondary storage Identify and describe storage media available for personal computers Differentiate among the principal types of secondary storage Explain how data is organized, accessed, and processed

6 October 16, 2002 Secondary Storage Benefits Semi-permanent Non-volatile Reliable Convenient – Locate and access data quickly

7 October 16, 2002 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 Secondary Storage Benefits

8 October 16, 2002 Types of Storage Magnetic Disk Storage Optical Disks – Magneto-optical – CD-ROM – CD-R – CD-RW – DVD-ROM Magnetic Tape Storage

9 October 16, 2002 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

10 October 16, 2002 Disk Capacity Size MB older hard disks GB current PC TB coming soon Whats stored? User documents Software Graphic images Audio files Video files

11 October 16, 2002 Diskettes Low capacity – small files Portable Flexible Mylar coated with metallic substance Hard plastic jacket for protection 3 ½ inch, 1.44 MB

12 October 16, 2002 High-Capacity Portable Disks Larger files Portable High-capacity – 120 / 200 MB – Can read and write standard diskettes – Ex: Superdisk Zip disk (Iomega Corp) – 250 MB – not compatible with 3 ½ inch diskettes – Also Jaz disk (2GB)

13 October 16, 2002 Data Compression Why use? – Squeeze big files onto small disks – Speed up data transfer of files Goal – Remove redundancy (minimize size) – Reduce to the minimal number of bits to store data 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 Different models used based on content (text, image, etc) – Must be decompressed to be used again

14 October 16, 2002 Hard Disk Various sizes Portability – Generally non-portable – Removable hard disks available for PC Rigid platter coated with metallic substance

15 October 16, 2002 Disk Pack Several platters Airtight, sealed module Mount disk pack on disk drive

16 October 16, 2002 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

17 October 16, 2002 Data Destroyed Head Crash

18 October 16, 2002 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 – Numbered 0 79 Each track stores the same amount of data

19 October 16, 2002 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

20 October 16, 2002 Same track on each platter Store files across multiple platters Reduces access time Logical Layout of a Disk Cylinder

21 October 16, 2002 Logical Layout of a Disk Zone Recording Assigns more sectors to tracks in outer zones More sectors = more data storage available

22 October 16, 2002 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

23 October 16, 2002 Access Time Components Seek time – Travel time for moving heads over track Head switching – Turning on correct head Rotational delay – Waiting for sector to arrive under head (Avg ½ revolution) Data transfer rate – Read/write bits on disk platter – Depends on density and rotational speed

24 October 16, 2002 Disk Caching Required data read from disk into memory Adjacent data read into disk cache (special area of memory) Program encounters a read instruction – Checks disk cache If present, no physical read is required If not present, read from disk

25 October 16, 2002 RAID Redundant Array of Independent Disks

26 October 16, 2002 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

27 October 16, 2002 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

28 October 16, 2002 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

29 October 16, 2002 CD-R Compact Disc-Recordable Cheap! – < 5 cents – or even free – Labels are the expensive part now High capacity Portable Write once Read multiple times – CD-R drive – CD-ROM drive

30 October 16, 2002 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

31 October 16, 2002 DVD-ROM Digital Versatile Disk Originally named Digital Video 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

32 October 16, 2002 Benefits – Full-length movies – Audio quality comparable to audio compact disks – High-volume business data Expected to replace CD-ROM in the near future DVD-ROM Digital Versatile Disk

33 October 16, 2002 Hardware – CD-ROM or DVD-ROM – Sound card or sound chip – Speakers MPEG (Motion Picture Experts Group) – Video standards that support full-motion video – Faster drive provides faster data transfer and produces a smoother video Applications Multimedia

34 October 16, 2002 Magnetic Tape Storage Plastic tape with magnetic coating Capacity based on density – bpi or cpi Magnetic tape unit – Read/write head – Erase head erases previously recorded data Inferior to disks – Not as reliable – Sequential access to data Inexpensive Primarily for backup

35 October 16, 2002 Backup Systems Prevent data loss – Fire – Natural disaster – Electromechanical failures of disk – User introduced errors – Software errors – Accidental data deletion Store data in more than one place – Important data must be kept offsite

36 October 16, 2002 Bit Rot How long is my data good? Not forever…… Bit rot occurs in all media – Bit rot is a degradation of the medium itself over time Worst Best.. – Floppy0 - 2 yrs – Tape 2 – 20 (with ECC) – Hard Disk5 yrs – CD-RW ? – CD-R ? – DVD???

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