Data Storage

	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.
	A storage device is a device used to store information for later use by a computer.
	In order to store and retrieve data properly it needs a storage system.
	Each operating system has its own data storage means, but there are common elements

Files

	Data on storage devices is stored in files.
	Files have names.
	They are stored on drives, which is a logical (not necessarily physical) device.

Drives

	Drives usually have a letter to represent them in the operating system.
	DOS and Windows PC’s floppy drives have the letters A and B
	Hard Drives, etc start with the letter C and go up: C, D, E, etc.
	Each different drive has its own letter.
	The main or boot Hard Drive usually has the letter C

Partitions

	One physical device or drive may be separated into several logical devices
	Each logical device can have a letter
	This is done by the OS
	For example one physical drive can be partitioned into several logical drives.
	Some OS’s such as Windows 2000 allow creating one large logical device from several smaller physical devices!

Folder or Directories

	Folders can have folders inside them and folders inside them, etc.

Folders

	A folder, sometimes called a directory is a division of a logical device.
	Floppy drives can hold hundreds of files.  Hard Drives and CD ROMS can hold 10's of thousands of files.
	Folders (previously called directories) help us organize our files into associated groups.
	Folders can exist inside folders
	My documents is a folder created by Windows 95

File and Folder Names

	Files and folders have names in order to be stored and retrieved.
	They also can have an extension.
	The extension is properly used to describe the type of file or folder.
	COM and EXE are extensions used for command and executable (program) files.
	BAT is a special program used in DOS, a batch file to execute commands
	TMP is temporary, DLL is dynamic link library.  Used a lot in Windows.

Permitted File Names

	In DOS, CPM, and other older operating systems file names were limited in size
	The Name or first part could be only 1-8 characters long
	The extension could be 0 to 3 characters long (not required)
	No spaces or special characters (?|%*) could be used in the name
	Only capital letters were used

File Specs

	The name is separated from the extension by a period (.)
	For example legal file names were: MYLETTER.DOC   MYLETTER  A  B.EXE
	Some modern OS’s do not show the extension.
	A File Specification is the location and name of the file
	For example C:\WINDOWS\COMMAND\CHKDSK.EXE

Windows 9X vs DOS vs Unix Names

	Windows 9X allows long names, spaces and upper and lower case in file names
	Win 9X keeps DOS names too.
	Win 9X does not properly handle upper and lower case
	Sending files with spaces and switched case causes problems
	Linux, Unix, MAC OS, DOS can have problems with file names
	Keep names simple, do not use spaces and mixed case in 9x

Data Files

	Data files hold data for use by command file programs.
	For example msword.exe, is the command file for the word processor, Microsoft Word.  It saves it’s documents with a doc extension.
	Smithletter.doc could be a MSWord document file.

Types of Data Files

	Common types of data files include:
		ASCII (text only)  Just words….
		Graphics (pictures) .bmp, .gif, .jpg, etc.
		Dynamic Link Libraries used by Win 95 programs  .dll  they do special functions!
		Audio files .wav, .mpg  they are sounds!
		Files can only be read and or changed by the type of software that created them!

Data Storage/Access Methods

	Data Devices can store data two ways
		Sequentially like a tape, where to get to the end you  must go through the whole tape
		Direct Access (sometimes called Random Access) where you can jump immediately to the data.  Hard disks, floppies, CD ROM’s etc. use this method
		ISAM or Indexed–Sequential Access used on some diskettes combines both methods