Junior Data

Binary and Hardware

by Gandalf

Two State Devices

Two-State Device is one which can exist ONLY in one of two states. Like the old expression, everything is Black and white ... there are no shades of grey. A common example of a Two-State device is a light switch, which can be either ON or OFF ... a switch cant be half on or half off.


Light Switch


Two State devices and Data

Two state devices can be used by computers to store information. The Binary code is used to store the data and this data can be used to encode almost any form of human readable data by using codes like ASCII for text or Bit maps for pictures.

Hard Drives

A hard drive is made up of milions and millions of two state devices. The drive is similar in concept to a record player, with a disk that spins and a read head on an arm that moves back and forth over the disk reading (and writing) the information on the disk.

Hard Drive


Inside a Hard Drive


Optical Drives

Optical drives - CD's and DVD's - work in a similar way to Hard drives. The surface of the CD/DVD disk is covered with aluminium (or sometimes gold). Small indentations (pits) in the surface of the disk are read by the CD/DVD drive.

Re-writable CDs and DVDs have a very thin layer of dye on their surface. A laser can create a series of tiny dots by heating the special pigment on the disks surface. The tiny dots produced emulate the pits in traditional optical media.

Optical Drive


Inside Optical Media


Binary Light Switches


Punch Card



  1. You should have a Digital Data mahara page. On your Digital Data page describe what a two state device is and relate this device to Binary data and ASCII.
  2. On your page describe how digital data is stored on hard drives and Optical Media like DVDs (make sure you include pictures)
  3. The picture above is a punch Card. Watch the video below about Punch Cards. Add the following information about punch cards to your Digital Data mahara pahe : 1. What a punch card is. 2. How data was encoded onto the card? 3. How is data was read by a card-reader? 4. How much data can be stored on a punch card. 5. Compare the punch card to a modern day hard drive in terms of storage capacity, speed of reading and writing and ease of use.

from here : http://web1.muirfield-h.schools.nsw.edu.au/curric/computing/datawiki/

Punch Cards