Understanding Computer Files and Data Management Systems

1. CSCI 1101 Intro to Computers 4. Computer File Systems

2. Remember - data/information distinctions • Data is words, numbers, and graphics that describe people, events, things, and ideas. • used by computers • Information is the words, numbers, and graphics used as the basis for human actions and decisions. • used by humans

3. File - named collection of data that exists on a storage medium such as a hard disk or floppy driv • Filename • unique set of letter and numbers • identifies a file • describes the file contents • Filenameextension further describes the file contents. • separated by the filename with a dot • You must provide a valid filename that adheres to rules or filenamingconventions.

4. What is a wildcard all about? • The asterisk is a wildcard character used to represent a group of characters in the filename or extension. • Wildcards are handy for finding specific files on a hard disk. • You can access files efficiently if you are familiar with the characteristics of file categories.

5. What is an executable file? • An executable file contains the program instructions that tell a computer how to perform a specific task. • Most have .exe or .com extensions. Executable files have .exe file extensions

6. What is contained in a data file? • A data file contains words, numbers, and pictures that you can view, edit, save, send, and print. • Passive, unlike executable files which are active • created using application software • receive data files on CD-ROMS such as clip art • You manipulate a data file using the same software that was used to create it.

7. How do you access a data file • The standard method for opening a data file is to start an application, then use the open command. • A generic filename extension indicates general type of data contained in a file. • a .bmp could be opened in Microsoft Paint or MicroGrafx Picture Publisher • An application-specificfilenameextension is associated with a particular application

8. Operating system files • Other files are necessary for hardware and software operations and should not be deleted.

9. File Management(Windows Explorer) • File manager utility software • provided by your computer operating system • helps you locate, rename, move, copy and delete files

10. Drive designations • A storage device, such as a floppy disk drive, a hard drive, and a CD-ROM drive, is identified by a letter called a device letter. • floppy disk drive = A • main hard disk = C • additional storage devices = D through Z

11. File directories • An operating system maintains a list of files called a directory for each disk, CD-ROM or DVD. • Directory includes • filename • filename extension • date and time file was created • file size • File extensions are frequently hidden in these displays, which can cause problems.

12. Operating system’s file manager utility displays lots of information about the files stored on a computer

13. What is the Root Directory? • Root directory • main directory of a disk • provides a useful list of files • Folders - smaller lists within directories • A folder is separated from a drive letter and a filename by a backslash (\).

14. Components of a complete file specification • A file specification (path) is the drive letter, folder, filename, and extension that identifies a file. A:\Word\Gumbo.doc extension filename drive letter subdirectory (folder)

15. Logical models for file management • File manager utility software provides a metaphorical view of the files stored on a computer. • also called logical models • filing cabinet • tree structure

16. Visualizing a disk storage structure • Visualize a disk directory as a tree. • trunk and branches are folders • leaves are files You can visualize the directory of a disk as a tree on its side.

17. Windows Explorer's view Windows Explorer

18. Common file management activities • Find - to locate a file • Rename - to change the name • Copy - to copy a file • Move - to move file from one folder to another • Delete - when you no longer need a file

19. Common Storage terminology • Storagemedium - the disk, tape, CD, DVD, paper, or other substance that contains data • Storagedevice - mechanical apparatus that records and retrieves data from a storage medium • floppy disk drives • hard disk drives • CD drives • DVD drives • tape drives

20. Storage activities • Storagetechnology - a storage device and the media it uses. • Storing - also known as • writing data (mainframe applications) • saving a file (Windows terminology) • Retrieving - also known as • reading data (mainframe applications) • loading data • opening a file (Windows terminology)

21. How is data (logically) stored • Computers use codes to convert information into digital data. • series of 1s and 0s • Bit - smallest unit for digitizing data • Byte - 8 bits • A byte represents: • a character • a space • numeral • punctuation

22. How is data physically stored • 1s and 0s are changed in the surface of the storage medium. • Transformation depends on storage technology. • Magneticstorage - stores data by magnetizing microscopic particles on the disk or tape surface • Read-writehead - mechanism in the disk drive that reads and writes magnetized particles that represent data

23. Magnetic surface storage Disk surface Read-write head Storing data on magnetic media Mylar disk

24. Limitations of magnetic storage • Data stored on magnetic media such as floppy disks can be altered by dust, smoke, heat, and mechanical problems. • Some experts estimate that the reliable life span of data stored on magnetic media is about three years.

25. Optical Storage technologies • Optical storage stores data as microscopic light spots (lands) and dark spots (pits) on the disk surface. • Data stored on an optical storage device is less susceptible to environmental damage.

26. Optical storage illustrated Optical storage devices read data using reflected laser light

27. How are disks organized? • Tracks - electronic storage bins • parallel to the edge of the tape • spiral out from the center of the disk • arranged as concentric circles or • Tracks that are arranged in concentric circles are divided into wedge-shaped sectors • Cluster - a group of sectors

28. Track / sector illustrations A formatted disk is divided into circular tracks

29. Why is a FAT important? • File allocation table (FAT) - an operating system file that maintains a list of files and their physical location on the disk. • like a table of contents • a damaged FAT results in losing data • Back up data on hard disk.

30. How files get stored • Computer looks for empty clusters to store data • Name of new file and number of cluster are recorded in the FAT • Files that do not fit in one cluster spill over to contiguous or noncontiguous clusters, depending on availability. • Pointers - instructions that point to each piece of the file

31. File storage illustration Each colored cluster represents part of a file

32. How does "undeleting" a file work? • When you delete a file, the clusters’ status becomes “empty” but retains old data until new data is stored. • You may be able to retrieve data using an undelete utility. • Recycle Bin’s Restore feature

33. What is fragmentation all about? • Files stored in many noncontiguous clusters become fragmented. • drive performance declines • becomes harder to locate clusters • A defragmentationutilityrearranges files in contiguous clusters • improves drive performance

34. There are many types of storage devices, each with unique advantages and disadvantages.

35. Data storage issues to consider • Versatility • can access data from different media • Durability • less susceptible to damage • Storage capacity - maximum amount of data that can be stored on a storage medium • kilobyte = approximately 1000 bytes • megabyte = approximately 1 million bytes • gigabyte = approximately 1 billion bytes • terabyte = approximately 1 trillion bytes

36. More issues to consider • Speed -measured by access time and data transfer rate • Access time - average time it takes a computer to locate data and read it • millisecond = one-thousandth of a second • Randomaccess- ability of a device to jump directly to the track or sector holding the data • floppy disk, hard drive, CD, DVD

37. What is a floppy disk? • Floppydisk - round piece of flexible mylar plastic covered with thin layer of magnetic oxide. • sealed in protective casing • also called floppies or diskettes • inside casing is “floppy” • not as speedy as zips • decreased use • Zipdisk - high-capacity floppy disk manufactured by Iomega Corporation.

38. How is a hard disk different? • Hard disk platter - a flat, rigid disk made of aluminum or glass and coated with magnetic oxide • density far exceeds floppy disk • Harddisk - one or more platters and their associated read-write heads. • preferred type of main storage • Cylinder • vertical set of tracks • basic storage bin for hard disk drive • Hard disks • provide random access to files • faster than floppy disk access • continually in motion

39. Hard disk illustration Hard disk platters prevent dust from interfering with read-write heads

40. What is a disk crash? • Headcrash - when a read-write head runs into a dust particle or other contaminant on the disk. • head crash damages some data on disk • triggered by jarring the hard disk while in use • Removableharddisk - hard disks that can be inserted and removed from drive • increase storage capacity • provides security for data

41. How do servers improve drive reliability? • RAID - (redundant array of independent disks) • type of hard disk storage • found on mainframe and microcomputer installations • contains many disk platters • provides redundancy • faster data access

42. CD essentials • CD-ROM • stands for Compact Disc Read-Only Memory • holds up to 680 MB • estimated life exceeds 500 years • inexpensive to manufacture • ideal for distribution of large files • choice for delivery of multimedia applications • read-only storage memory • Read-only - computer can retrieve from it but not save new data on it

43. CD variants • CD-R • stands for compact disc-recordable • allows you to create your own CDs by recording on a CD-R disk • Recording is done on a CD-R drive • uses a laser to change the reflectivity of a dye layer on a blank CD-R disk.

44. Uses for CD-R drives • Disks produced on CD-R drive • can be used on CD-ROM and DVD drives • cannot be erased or modified • some drives have multisessionsupport (can record in multiple sessions) • available after 1998 • Archiving - moving data that is not accessed frequently off of a primary storage device

45. What about reusable CDs? • CD-RW (compact disc-rewritable) allows you to write on a CD, then change the data • requires special CD-RW disks • requires special CD-RW drive • requires phase change technology • Phase change technology - alters the crystal structure on the disk surface

46. How is DVD different from CD technology? • DVD (digital video disc or digital versatile disc) • variation of CD technology • designed to provide enough storage capacity for a full length movie • will replace video tape (experts believe) • DVD-ROM disk • stamped with data when manufactured • cannot change or add data • stores 4.7 GB • ideal for games, maps, large databases

47. Reusable DVD issues • DVD+RW • uses phase change technology • cannot be used on DVD-RAM • DVD-RAM • uses a blend of technologies to record data • cannot be used on DVD+RW • Both DVD+RW and DVD-RAM can be read on DVD-ROM drives.