CSCI 1101 Intro to Computers 4 Computer File
- Slides: 47
CSCI 1101 Intro to Computers 4. Computer File Systems
Remember - data/information distinctions n Data is words, numbers, and graphics that describe people, events, things, and ideas. à used n by computers Information is the words, numbers, and graphics used as the basis for human actions and decisions. à used by humans
n n File - named collection of data that exists on a storage medium such as a hard disk or floppy driv Filename à à à n Filename extension further describes the file contents. à n unique set of letter and numbers identifies a file describes the file contents separated by the filename with a dot You must provide a valid filename that adheres to rules or file naming conventions.
What is a wildcard all about? n n n 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.
What is an executable file? An executable file contains the program instructions that tell a computer how to perform a specific task. n Most have. exe or. com extensions. Executable n files have. exe file extensions
What is contained in a data file? n A data file contains words, numbers, and pictures that you can view, edit, save, send, and print. à Passive, unlike executable files which are active à created using application software à receive data files on CD-ROMS such as clip art n You manipulate a data file using the same software that was used to create it.
How do you access a data file n n 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. à n a. bmp could be opened in Microsoft Paint or Micro. Grafx Picture Publisher An application-specific filename extension is associated with a particular application
Operating system files n Other files are necessary for hardware and software operations and should not be deleted.
File Management (Windows Explorer) n File manager utility software à provided by your computer operating system à helps you locate, rename, move, copy and delete files
Drive designations n 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. à floppy disk drive = A à main hard disk = C à additional storage devices = D through Z
File directories n n An operating system maintains a list of files called a directory for each disk, CD-ROM or DVD. Directory includes à à n filename extension date and time file was created file size File extensions are frequently hidden in these displays, which can cause problems.
Operating system’s file manager utility displays lots of information about the files stored on a computer
What is the Root Directory? n Root directory à main directory of a disk à provides a useful list of files n n Folders - smaller lists within directories A folder is separated from a drive letter and a filename by a backslash ().
Components of a complete file specification § A file specification (path) is the drive letter, folder, filename, and extension that identifies a file. A: WordGumbo. doc extension filename drive letter subdirectory (folder)
Logical models for file management n File manager utility software provides a metaphorical view of the files stored on a computer. à also called logical models p filing cabinet p tree structure
Visualizing a disk storage structure n Visualize a disk directory as a tree. à trunk and branches are folders à leaves are files You can visualize the directory of a disk as a tree on its side.
Windows Explorer's view Windows Explorer
Common file management activities n n n 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
Common Storage terminology n n Storage medium - the disk, tape, CD, DVD, paper, or other substance that contains data Storage device - mechanical apparatus that records and retrieves data from a storage medium à à à floppy disk drives hard disk drives CD drives DVD drives tape drives
Storage activities n n Storage technology - a storage device and the media it uses. Storing - also known as à writing data (mainframe applications) à saving a file (Windows terminology) n Retrieving - also known as à reading data (mainframe applications) à loading data à opening a file (Windows terminology)
How is data (logically) stored n Computers use codes to convert information into digital data. à n n n series of 1 s and 0 s Bit - smallest unit for digitizing data Byte - 8 bits A byte represents: à à a character a space numeral punctuation
How is data physically stored n n 1 s and 0 s are changed in the surface of the storage medium. Transformation depends on storage technology. Magnetic storage - stores data by magnetizing microscopic particles on the disk or tape surface Read-write head - mechanism in the disk drive that reads and writes magnetized particles that represent data
Magnetic surface storage Disk surface Storing data on magnetic media Read-write head Mylar disk
Limitations of magnetic storage n n 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.
Optical Storage technologies n n 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.
Optical storage illustrated Optical storage devices read data using reflected laser light
How are disks organized? n Tracks - electronic storage bins à parallel to the edge of the tape à spiral out from the center of the disk à arranged as concentric circles or n n Tracks that are arranged in concentric circles are divided into wedge-shaped sectors Cluster - a group of sectors
Track / sector illustrations A formatted disk is divided into circular tracks
Why is a FAT important? n File allocation table (FAT) - an operating system file that maintains a list of files and their physical location on the disk. à like a table of contents à a damaged FAT results in losing data n Back up data on hard disk.
How files get stored n n 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
File storage illustration Each colored cluster represents part of a file
How does "undeleting" a file work? n n 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. à Recycle Bin’s Restore feature
What is fragmentation all about? n Files stored in many noncontiguous clusters become fragmented. à drive performance declines à becomes harder to locate clusters n A defragmentation utility rearranges files in contiguous clusters à improves drive performance
n There are many types of storage devices, each with unique advantages and disadvantages.
Data storage issues to consider n Versatility à n Durability à n can access data from different media less susceptible to damage Storage capacity - maximum amount of data that can be stored on a storage medium à à kilobyte = approximately 1000 bytes megabyte = approximately 1 million bytes gigabyte = approximately 1 billion bytes terabyte = approximately 1 trillion bytes
More issues to consider n n Speed - measured by access time and data transfer rate Access time - average time it takes a computer to locate data and read it à millisecond n = one-thousandth of a second Random access - ability of a device to jump directly to the track or sector holding the data à floppy disk, hard drive, CD, DVD
What is a floppy disk? n Floppy disk - round piece of flexible mylar plastic covered with thin layer of magnetic oxide. à à à n sealed in protective casing also called floppies or diskettes inside casing is “floppy” not as speedy as zips decreased use Zip disk - high-capacity floppy disk manufactured by Iomega Corporation.
How is a hard disk different? n Hard disk platter - a flat, rigid disk made of aluminum or glass and coated with magnetic oxide à n Hard disk - one or more platters and their associated read-write heads. à n preferred type of main storage Cylinder à à n density far exceeds floppy disk vertical set of tracks basic storage bin for hard disk drive Hard disks à à à provide random access to files faster than floppy disk access continually in motion
Hard disk illustration Hard disk platters prevent dust from interfering with read-write heads
What is a disk crash? n Head crash - when a read-write head runs into a dust particle or other contaminant on the disk. à à n head crash damages some data on disk triggered by jarring the hard disk while in use Removable hard disk - hard disks that can be inserted and removed from drive à à increase storage capacity provides security for data
How do servers improve drive reliability? n RAID - (redundant array of independent disks) à type of hard disk storage à found on mainframe and microcomputer installations à contains many disk platters à provides redundancy à faster data access
CD essentials n CD-ROM à à à à n 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
CD variants n CD-R à stands for compact disc-recordable à allows you to create your own CDs by recording on a CD-R disk n Recording is done on a CD-R drive à uses a laser to change the reflectivity of a dye layer on a blank CD-R disk.
Uses for CD-R drives n Disks produced on CD-R drive à can be used on CD-ROM and DVD drives à cannot be erased or modified à some drives have multisession support (can record in multiple sessions) p available n after 1998 Archiving - moving data that is not accessed frequently off of a primary storage device
What about reusable CDs? n CD-RW (compact disc-rewritable) allows you to write on a CD, then change the data à requires special CD-RW disks à requires special CD-RW drive à requires phase change technology n Phase change technology - alters the crystal structure on the disk surface
How is DVD different from CD technology? n DVD (digital video disc or digital versatile disc) à à à n variation of CD technology designed to provide enough storage capacity for a full length movie will replace video tape (experts believe) DVD-ROM disk à à stamped with data when manufactured cannot change or add data stores 4. 7 GB ideal for games, maps, large databases
Reusable DVD issues n DVD+RW à uses phase change technology à cannot be used on DVD-RAM à uses a blend of technologies to record data à cannot be used on DVD+RW n Both DVD+RW and DVD-RAM can be read on DVD-ROM drives.
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