1. B.A. (Mahayana Studies) 000-209 Introduction to Computer Science November 2005 - March 2006 4. Files and Data Storage What are the different kinds of file you'll meet? How can data (files) be stored?

2. 000-209 Intro to CS. 4/Data 2 Overview 1. What is a File?  the different types of file you may meet 2. Drives, Folders, and Files  how files are organized on a storage device 3. Storage Devices  different types of storage device 4. Magnetic Storage (e.g. hard disks) 5. Optical Storage (e.g. CDs)

3. 000-209 Intro to CS. 4/Data 3 A file contains data. Every file has a filename. Most filenames end with an extension (after the dot):  e.g slides.ppt, report.doc The file may be stored on your computer, or on a floppy/CD/flash drive. 1. What is a File?

4. 000-209 Intro to CS. 4/Data 4 An executable file contains program instructions that tell a computer how to do a task. Most have.exe or.com extensions. 1.1. What is an Executable File?

5. 000-209 Intro to CS. 4/Data 5 A data file contains words, numbers, or pictures that you can view, edit, save, send, and print.  no program instructions  created using application software You manipulate a data file using the same software that created it. 1.2. What is a Data File?

6. 000-209 Intro to CS. 4/Data 6 Try double clicking on the file's icon, or start an application and use its 'open' command. Often the filename extension is associated with a particular application  e.g..doc is associated with MS Word  double clicking on a.doc file causes Word to start, and open the file 1.3. Accessing a Data File

7. 000-209 Intro to CS. 4/Data 7 1.4. Common OS Files

8. 000-209 Intro to CS. 4/Data 8 1.5. File Management Windows Explorer in MS Windows

9. 000-209 Intro to CS. 4/Data 9 2. Drives, Folders, and Files Files are grouped into folders (directories). Folders may be grouped together inside other folders. Folders are located on drives  a drive may be your computer's hard disk, floppy, flash drive, CD  a drive is a storage device

10. 000-209 Intro to CS. 4/Data 10 drives folders files

11. 000-209 Intro to CS. 4/Data 11 You can think of a drive as a tree on its side.  the trunk and branches are the drive's folders  the leaves are the files 2.1. Visualizing a Drive

12. 000-209 Intro to CS. 4/Data 12 Windows Explorer

13. 000-209 Intro to CS. 4/Data 13 A drive is identified by a letter.  floppy disk drive = A  main hard disk = C  additional storage devices = D through Z 2.2. Drive Letters

14. 000-209 Intro to CS. 4/Data 14 The folder can show each file's:  name  extension  date and time file it was created/modified  file size Extensions are often hidden in these displays, which can be confusing. 2.3. Directory Information

15. 000-209 Intro to CS. 4/Data 15 A path to a file includes its drive letter, folder(s), filename, and extension. A:\Word\Reports\To-Do.doc folders (subdirectories) filename extension drive letter 2.4. The Path to a File

16. 000-209 Intro to CS. 4/Data 16 Storage devices include:  floppy disks, hard disks, CDs, flash drives, tapes 3. Storage Devices

17. 000-209 Intro to CS. 4/Data 17 Durability: how easy is it to damage the device? Storage capacity: how much data can be stored on the device?  kilobyte (KB) = about 1000 bytes  megabyte (MB) = about 1 million bytes (10 6 )  gigabyte (GB) = about 1 billion bytes (10 9 )  terabyte (TB) = about 1 trillion bytes (10 12 ) 3.1. Which Storage Device to Use?

18. 000-209 Intro to CS. 4/Data 18 Speed: read/write time and data transfer rate Access time: average time to locate data  millisecond = one-thousandth of a second (10 -3 ) Random access: can the device go directly to the track or sector holding the data?  possible with floppy disks, hard drives, CDs, DVDs  not possible with magnetic tape

19. 000-209 Intro to CS. 4/Data 19 The text/images/sound/etc. in a file are converted to a (very) long series of 1's and 0's. A single '1' or '0' is called a bit. Bits are grouped together into bytes  a byte is 8 bits When text is converted, each character is translated into one byte. 3.2. How is Data Stored?

20. 000-209 Intro to CS. 4/Data 20 A file is just a series of bits. Each bit is either '1' or '0', so can be represented by a magnetized particle with a positive or negative charge. Bits are stored as a series of magnetized particles on the surface of a magnetic disk or tape. 4. Magnetic Storage

21. 000-209 Intro to CS. 4/Data 21 The particles are magnetized (written) or examined (read) using a read-write head that moves over the disk/tape. Example magnetic devices are:  hard drives, floppy disks, tapes

22. 000-209 Intro to CS. 4/Data 22 Read-write head Disk surface Mylar disk Disk Storage Diagram

23. 000-209 Intro to CS. 4/Data 23 Data stored on magnetic media, such as a floppy disks, can be altered by dust, smoke, heat, and mechanical problems. The reliable life span of data stored on magnetic media is only about 3 years. 4.1. Limitations of Magnetic Storage

24. 000-209 Intro to CS. 4/Data 24 4.2. How a Hard Disk is Organized : rotation arm platter cylinder track read-write head spindle actuator sector

25. 000-209 Intro to CS. 4/Data 25 Track/Sector in Close-up track sector

26. 000-209 Intro to CS. 4/Data 26 Hard Disk Picture

27. 000-209 Intro to CS. 4/Data 27 The OS looks for sequences of empty tracks (called clusters) to store the file's data. Data that is too big for one cluster is split up over nearby clusters. 4.3. How a File is Stored

28. 000-209 Intro to CS. 4/Data 28 When a file is deleted, its clusters are marked as 'empty' but the old data is left in the clusters until new data is stored there. You may be able to retrieve the old data using an undelete utility.  e.g. Window’s Restore utility, Norton SystemWorks  the data will only be available if the clusters have not been reused 4.4. Undeleting a file

29. 000-209 Intro to CS. 4/Data 29 Files stored in many widley-spaced clusters become fragmented.  read/write speed is slow  finding clusters requires a longer search A defragmentation utility rearranges a file into nearby clusters  improves read/write/search speed  e.g Windows Disk Defragmenter 4.5. Data Fragmentation

30. 000-209 Intro to CS. 4/Data 30 A head crash occurs when a read-write head runs into a dust particle or other dirt on the disk  the head crash may damage some of the magnetic particles on the disk, changing or losing the data stored there A head crash may also be triggered by knocking the hard disk while it is in use. 4.6. What is a Hard Disk Crash?

31. 000-209 Intro to CS. 4/Data 31 RAID - redundant array of independent disks  used in large mainframe and microcomputer installations  provides faster data access since can do several accesses at once  resists failure since data can be duplicated 4.7. RAID

32. 000-209 Intro to CS. 4/Data 32 An optical storage device stores bits as microscopic light spots (lands) and dark spots (pits) on its surface  examples are CDs, DVDs Data stored on an optical storage device is less easy to damage. 5. Optical Storage

33. 000-209 Intro to CS. 4/Data 33 Read the data using reflected laser light. Optical Storage Illustrated

34. 000-209 Intro to CS. 4/Data 34 CD-ROM  Compact Disc Read-Only Memory  holds up to 680 MB  estimated life exceeds 500 years  cheap to make  ideal for large files (e.g. multimedia applications) 5.1. CDs

35. 000-209 Intro to CS. 4/Data 35 CD-RW (compact disc-rewritable) allows you to write on a CD, then change the data later  uses phase change technology Phase change technology: alter the crystal structure on the disk surface

36. 000-209 Intro to CS. 4/Data 36 Digital Video Disc  variation of CD technology  designed to provide enough storage capacity for a full length movie DVD-ROM  stamped with data when manufactured  cannot change or add data  stores 4.7 GB  ideal for games, maps, large databases DVD+RW  uses phase change technology for reuseability 5.2. DVDs