4.1) Storage Fundamentals
  
  RAM - Random Access Memory - stored in an electronic state during processing
  
  Secondary Storage - holds data even when computer is turned off
  
  Units of storage
    Kilobyte:	  K or KB	1024 bytes
    Megabyte:	  M or MB	~1 million bytes
    Gigabyte:	  G or GB	~1 billion bytes
    Terabyte:	  T or TB	~1 trillion bytes
	
  reading - retrieving data for secondary storage medium
  writing - transferring data to secondary storage medium
  
  
  Sequential Storage - data is stored in a logical order; usually alphabetical
    pro: increases access time when data must be accessed in sequential order
    con: slow when data needs to be accessed in random order
	
  Direct Access Storage - also called random access storage
    pro: increases access time when data must be accessed in random order
    con: slow when data needs to be accessed in sequential order
   
  Indexed Sequential Access Method - ISAM - is random access storage, but a
    separate index is created that links a sequential list to the randomly
    stored data.
	
File types:

  Program files - contain software instructions.  Also called executable files 
    and usually have the .exe file extension.

  Data files - often called document files, contain data not programs.  This 
    data has been created and can be manipulated by applications software.
	
  ASCII files - text only files.  .html and .txt files are common examples.
  
  Image files - contain digitized graphics
  
  Audio and video files - contain digitized sound or graphics
  
  
  
4.2) Tape storage

  Cassettes used for backup storage.  Can be magnetic tapes or cartridge tapes. 
  
4.3) Diskette storage

  also called floppy disk.  A removable, round piece of  flexible plastic that 
  stores data.  All conventional diskettes are enclosed in a square plastic case 
  for protection.
	
  Characteristics of diskettes
    tracks - a concentric circle for storing data.
    sector - a wedge section of the diskette.  Each sector contains a section
      of multiple tracks and hold ~512 bytes.
	  
  Unformatted vs. Formatted - an unformatted diskette can be written to by a
    microcomputer.  Microcompters can format diskettes to make them usable.
    Macs and PCs have different standards for formatting, also newer Macs
    can typically read and write to PC formatted diskettes also.
	
  Data capacity: the amount of data a diskette can hold.  Most 3.5" floppy
  disks or High Density (HD for short) and can hold 1.44 MB of info.
	
  Write protect feature: That tab thingy that you can slide on a floppy disk.
    When you can see the hole, you can not write to the disk.  The tab can
    also be removed completely which will prevent the disk from ever being
    written to again.
	
  Note: do not remove disk when light is on.
	
4.4) Hard Disks

  Hold data in magnetized spots, so data is stored even when computer is off.
  Have high capacity for data; typically hold 4 MB of data or more.
  Thin metal or glass rigid disk.
  
  Nonremovable Internal Hard Disks - inside the computer.  Have several arms
    like a record player for reading and writing data to the several disks 
    inside the drive.
	
  pro: capacity and speed.  A fast drive has seek time of 6 ms.
  
  con: possible "head crash".  The arms are not supposed to touch the disk,
    but instead ride on a thin cushion of air.  If a particle of dust gets 
    stuck between the arm and disk, that can cause a "head crash" and loss of
    data.  Sudden jarring while the hard disk is in use can also cause this
    problem

Hard Disk Architectures:
	
  EIDE - Enhanced Integrated Drive Electronics - a type of hardware interface 
  that is commonly used to connect internal components such as the hard
  drive and CD-ROM drive to the rest of the PC.  Can attain rate of
  16.6 MB per second.  Has a low manufacturing cost.
	
  SCSI - Small Computer System Interface - the type of hardware interface used
  on Macs and high-end PCs.  Allows 7-15 devices.  SCSI-2 can attain rates of
  20-40 MB per second.  Ultra 3 SCSI, 160 MB per second.
	
Variations

  External Hard Drives:  A hard drive that is outside the computer. 
	
  Hard Disk Cartridges - also called removable hard disks.  Include things like
    Zip disks (100 or 250 MB capacity)
    Jaz disks {1 or 2 GB capacity)
    SyQuest's Syjet (44 MB capacity)
	
Virtual Memory:

  Many newer computers allow you to use you hard disk to extend the RAM.  This
  is call Virtual Memory.  This increases the processing power of your
  computer but is slow because it has to read and write data from the 
  hard disk instead of just processing everything in the RAM.
  
  Removable pack - hard disk system contains 6-20 hard disks.
  
  Fixed disk drives - have greater storage capacity than conventional
    hard drives.  A mainframe may contain 20-100 fixed disks.
	
  RAID - Redundant Array of Inexpensive Disks.  2 or more drives connected
    via a SCI train.  Holds more data and is more reliable than Fixed Disk
    Drives.
	
Future:
  Hard disks will have two heads per surface, one for reading and one for
  writing.  This will increase access speed.
  
4.5) Optical Disks

  Read data optically via a laser.
	 
  CD-ROM - Compact Disk Read Only Memory.  Can hold 650 MB to 1 GB.
    A 1x CD-ROM drive reads at 150 KB per second.
    A 40x CD-ROM drive reads at 6 MB per second.
	
  CD-R - Compact Disk Recordable
  
  CD-RW - Compact Disk ReWritable.  A type Magneto-Optical (MO) disks.
    
	Superdisks - also MO disks.  Can hold 120 MB to 250 MB.
	
  DVD-ROM - originally stood for "Digital Video Disk", then "Digital Versatile
    Disk", but now doesn't stand for anything.  Can be single sided, double
    sided, double layered, or double layered and double sided.  Capacity
    therefore ranges from 4.7 GB to 17 GB.
	
	What are the promises of DVD?
	
	note: Music can now be bought on DVD.  
    The DVD standard for sound quality is: 96   Khz at 24 bit stereo.  
    Compare with CD quality:               44.1 khz at 16 bit stereo.
   
4.6) The Importance of Backup

  Simple really.  Anything that is material can break or get damaged, whether
  it is due to regular wear and tear or a catastrophic emergency.  Most companies
  have multiple backups of important data in different physical locations,
  sometimes different parts of the country and all over the world.
  
  The most important factor in choosing a backup storage medium to suit your
  needs is cost.  The second is speed.  The third is ease of use.
  
  Many computer users simply use a second hard drive as backup storage because 
  the cost of such hardware is relatively low compared to other mediums,
  and it is by far the easiest and fastest.  Can also use a partition
  of a drive.   
   
4.7) Other forms of secondary storage

  Flash Memory - also called flash RAM cards.  Can hold data electronically
    but keep the data even when the power is cut off.  Hold up to 100 MB.
	
Game?Game?		

Homework 4:
in Interactive computing book
WD 4.2 - 4.33 
WD 4.34 #3 will be turned in via e-mail.
   e-mail your tables and charts as an attached Word doc to Mike Kolta.
   Due date: 2/13 at midnight.