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RAM is volatile, yet that is where all the data
is stored while it is being processed.
Data to be used later and results of processing other data should be
placed in more stable memory. |
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A storage device is a device used to store
information for later use by a computer. |
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In order to store and retrieve data properly it
needs a storage system. |
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Each operating system has its own data storage
means, but there are common elements |
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Data on storage devices is stored in files. |
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Files have names. |
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They are stored on drives, which is a logical
(not necessarily physical) device. |
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Drives usually have a letter to represent them
in the operating system. |
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DOS and Windows PC’s floppy drives have the
letters A and B |
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Hard Drives, etc start with the letter C and go
up: C, D, E, etc. |
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Each different drive has its own letter. |
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The main or boot Hard Drive usually has the
letter C |
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One physical device or drive may be separated
into several logical devices |
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Each logical device can have a letter |
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This is done by the OS |
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For example one physical drive can be
partitioned into several logical drives. |
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Some OS’s such as Windows 2000 allow creating
one large logical device from several smaller physical devices! |
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Folders can have folders inside them and folders
inside them, etc. |
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A folder, sometimes called a directory is a
division of a logical device. |
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Floppy drives can hold hundreds of files. Hard Drives and CD ROMS can hold 10's of
thousands of files. |
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Folders (previously called directories) help us
organize our files into associated groups. |
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Folders can exist inside folders |
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My documents is a folder created by Windows 95 |
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Files and folders have names in order to be
stored and retrieved. |
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They also can have an extension. |
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The extension is properly used to describe the
type of file or folder. |
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COM and EXE are extensions used for command and
executable (program) files. |
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BAT is a special program used in DOS, a batch
file to execute commands |
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TMP is temporary, DLL is dynamic link
library. Used a lot in Windows. |
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In DOS, CPM, and other older operating systems
file names were limited in size |
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The Name or first part could be only 1-8
characters long |
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The extension could be 0 to 3 characters long
(not required) |
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No spaces or special characters (?|%*) could be
used in the name |
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Only capital letters were used |
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The name is separated from the extension by a
period (.) |
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For example legal file names were:
MYLETTER.DOC MYLETTER A
B.EXE |
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Some modern OS’s do not show the extension. |
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A File Specification is the location and name of
the file |
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For example C:\WINDOWS\COMMAND\CHKDSK.EXE |
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Windows 9X allows long names, spaces and upper
and lower case in file names |
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Win 9X keeps DOS names too. |
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Win 9X does not properly handle upper and lower
case |
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Sending files with spaces and switched case
causes problems |
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Linux, Unix, MAC OS, DOS can have problems with
file names |
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Keep names simple, do not use spaces and mixed
case in 9x |
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Data files hold data for use by command file
programs. |
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For example msword.exe, is the command file for
the word processor, Microsoft Word.
It saves it’s documents with a doc extension. |
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Smithletter.doc could be a MSWord document file. |
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Common types of data files include: |
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ASCII
(text only) Just words…. |
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Graphics (pictures) .bmp, .gif, .jpg, etc. |
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Dynamic Link Libraries used by Win 95
programs .dll they do special functions! |
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Audio files .wav, .mpg they are sounds! |
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Files can only be read and or changed by the
type of software that created them! |
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Data Devices can store data two ways |
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Sequentially like a tape, where to get to the
end you must go through the whole
tape |
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Direct Access (sometimes called Random Access)
where you can jump immediately to the data. Hard disks, floppies, CD ROM’s etc. use this method |
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ISAM or Indexed–Sequential Access used on some
diskettes combines both methods |
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Notes
