Secondary Storage
* Why Storage is Necessary
* Different Forms of Storage
* Advantages and Disadvantages of Storage Forms
* How Computer Files are Organized

Why Secondary Storage*
* Cheaper
* Larger Capacity
* NON-Volatile


Data Storage Hierarchy
                           Small Capacity
Most Expensive						Fastest



Least Expensive						Slowest

				Large Capacity

Secondary Storage - Magnetic
* Magnetic Tape 
* Magnetic Disks
* Floppy Disks
* Hard Disks
* Zip Disks
* Bernoulli Disks

Secondary Storage:
 Magnetic Tape

		 Supply Reel 	


				
						  tape loops in
						  vacuum chambers
MAGNETIC TAPE
							
							9 TRACKS



8BITS + PARITY BIT

DATA STORED ACROSS THE TAPE

READING FROM TAPES
* SEQUENTIAL ONLY
* INTERRECORD GAP
* .6" 
* FOR START AND STOP
* WASTED SPACE
* BLOCKING

BLOCKING RECORDS
* LOGICAL RECORD
* PHYSICAL RECORD
* SEVERAL LOGICAL IN EACH PHYSICAL = BLOCKED RECORDS
* BLOCKING SAVES
* SPACE
* TIME

MAGNETIC DISKS
RANDOM ACCESS (Direct)
Magnetic Disk Preparation (Formatting)
* Tracks
* Sectors
* Hard Disk Interfaces
* IDE
* SCSI

MAGNETIC DISKS
* FLOPPY
* mylar plastic 
* HARD 
* Machined aluminum
* 3600 rpm
* read/write head "floats" .000020 inch
* jet; 600mph; 1/4 inch


HEAD CRASH
* Disks Are Vulnerable
* Dust, Smoke, Fingerprint, Hair


DISK ACCESS TIME
* Seek time
* Minimized through use of CYLINDERS
* Rotational delay
* Data transfer time

Secondary Storage - Other Forms
* Optical Disk
* Lasers burn "pits" and "lands"
* Types
* CD-ROM
* WORM
* MO

File Types
* Program Files
* Support Files
* Data Files
* Configuration Files
* Text Files
* Graphics Files
* Spreadsheet Files
* Database Files
* Sound Files
* Backup Files

Naming Files
* MS-DOS and Windows 3.1
* File Names 
* Extensions
* Windows 95
* File Names
* Extensions
* Macintosh

Organizing Files into Directories
* Root Directory (Folder)
* Subdirectories (Subfolder)
* Files

Data Storage Hierarchy
* Character (Bits)
* Field
* Record
* File

File Organization
* Sequential
* Direct (Random)
* Indexed Sequential