Download - CSCI 1101 Intro to Computers
CSCI 1101 Intro to Computers
4. Computer File Systems
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
Remember - data/information distinctions
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
Filename extension further 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.
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 a wildcard all about?
An executable file contains the program instructions that tell a computer how to perform a specific task.
Most have .exe or .com extensions.Executablefiles have .exe fileextensions
What is an executable 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.
What is contained in 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-specific filename extension is associated with a particular application
How do you access a data file
Other files are necessary for hardware and software operations and should not be deleted.
F I G U R E 4 - 8
F i l e n a m e E x t e n s i o n s f o r C o n f i g u r a t i o n F i l e s
a n d P r o g r a m M o d u l e s
T yp e o f F i l e D e s c r i p t i o n F i l e n a m e
E x t e n s i o n
B a t c h f i l e A s e q u e n c e o f o p e r a t i n g s y s t e m c o m m a n d s t h a t a r e
e x e c u t e d a u t o m a t i c a l l y w h e n t h e c o m p u t e r b o o t s .
. b a t
C o n f i g u r a t i o n f i l e I n f o r m a t i o n a b o u t p r o g r a m s t h a t t h e c o m p u t e r u s e s
t o a l l o c a t e t h e r e s o u r c e s n e c e s s a r y t o r u n t h e m .
. c f g , . s y s ,
. m i f , . i n i
H e l p T h e i n f o r m a t i o n t h a t i s d i s p l a y e d b y o n l i n e H e l p . . h l p
T e m p o r a r y f i l e A s o r t o f “ s c r a t c h p a d ” t h a t c o n t a i n s d a t a w h i l e a
p r o g r a m i s r u n n i n g , b u t t h a t i s d i s c a r d e d w h e n
y o u e x i t t h e p r o g r a m .
. t m p
P r o g r a m s u p p o r t
m o d u l e s
P r o g r a m i n s t r u c t i o n s t h a t a r e e x e c u t e d i n
c o n j u n c t i o n w i t h t h e m a i n . e x e f i l e f o r a p r o g r a m .
. o c x , . v b x ,
. d l l
Operating system files
File manager utility software provided by your computer operating system helps you locate, rename, move, copy and delete
files
File Management(Windows Explorer)
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
Drive designations
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.
File directories
Operatingsystem’s file managerutility displayslots of informationabout the filesstored on acomputer
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 (\).
What is the Root Directory?
A file specification (path) is the drive letter, folder, filename, and extension that identifies a file.
A:\Word\Gumbo.doc
subdirectory (folder)
filename
extension
drive letter
Components of a complete file specification
File manager utility software provides a metaphorical view of the files stored on a computer. also called logical models
filing cabinet tree structure
Logical models for file management
You can visualizethe directoryof a disk as a tree on its side.
Visualize a disk directory as a tree. trunk and branches
are folders leaves are files
Visualizing a disk storage structure
WindowsExplorer
Windows Explorer's view
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 file management activities
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 floppy disk drives hard disk drives CD drives DVD drives tape drives
Common Storage terminology
Storage technology - 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)
Storage activities
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
How is data (logically) stored
1s and 0s 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
How is data physically stored
Storing dataon magneticmedia
Read-write head
Disk surface
Mylar disk
Magnetic surface 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.
Limitations of magnetic storage
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 technologies
Optical storage devicesread data using reflectedlaser light
Optical storage illustrated
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
How are disks organized?
A formatteddisk is divided intocircular tracks
Track / sector illustrations
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.
Why is a FAT important?
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
How files get stored
Each coloredclusterrepresentspart of a file
File storage illustration
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
How does "undeleting" a file work?
Files stored in many noncontiguous clusters become fragmented. drive performance declines becomes harder to locate clusters
A defragmentation utility rearranges files in contiguous clusters improves drive performance
What is fragmentation all about?
There are many types of storage devices, each with unique advantages and disadvantages.
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
Data storage 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
Random access - ability of a device to jump directly to the track or sector holding the data floppy disk, hard drive, CD, DVD
More issues to consider
Floppy disk - 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
Zip disk - high-capacity floppy disk manufactured by Iomega Corporation.
What is a floppy disk?
Hard disk platter - a flat, rigid disk made of aluminum or glass and coated with magnetic oxide density far exceeds floppy disk
Hard disk - 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
How is a hard disk different?
Hard diskplatters preventdust from interfering withread-writeheads
Hard disk illustration
Head crash - 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
Removable hard disk - hard disks that can be inserted and removed from drive increase storage capacity provides security for data
What is a disk crash?
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
How do servers improve drive reliability?
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
CD essentials
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.
CD variants
Disks produced on CD-R drive can be used on CD-ROM and DVD drives cannot be erased or modified some drives have multisession support (can
record in multiple sessions) available after 1998
Archiving - moving data that is not accessed frequently off of a primary storage device
Uses for CD-R drives
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
What about reusable CDs?
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
How is DVD different from CD technology?
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.
Reusable DVD issues