The 6 different physical states of digital signals by Matt Ottewill

Digital computing involves using electronics to represent 1's and 0's (binary). These 1's and 0's can take 6 different "physical" forms as they travel between and through the various hardware components of a digital computing system.

In a computer system, binary data may exist in several different forms at different times ...

  1. Electrical pulse waves
  2. Positions of switches (RAM etc memory)
  3. Patterns of magnetic flux
  4. Pits and lands or differing coloured dyes on the surface of an optical disc (CD, DVD etc)
  5. Radio signals sent over a wireless network
  6. Pulses of light sent down an optical cable

 

1. Electrical pulse wave

When traveling between components such as ...

  • a CD drive/disc and RAM memory
  • a MIDI keyboard and MIDI interface
  • a computer and a connected printer
  • a modem and the internet
  • a scanner and RAM memory
  • etc

... a binary data stream takes the form of an electrical pulse wave. Pulse waves are used because they are ideal for representing the on/off states of binary bits.

2. Positions of switches (RAM & CPU etc)

When a binary electrical pulse wave has arrived at a RAM, FlashRAM or ROM memory module or the CPU, the waves on/off states are translated into on/off positions of millions of switches (transistors) which temporarily "hold" the binary values.


3. Patterns of magnetic flux (on floppy, removable& hard disks)

On the surface of a floppy disc or hard drive, 1s and 0s are recorded as a pattern of strong and weak magnetic pulses. More on hard disc drives is here.


4. Pits and lands / light sensitive surfaces (optical media)

Pressed / manufactured optical discs

A master disc is created from which copies are made. The master is created with a laser which turns on and off according to the data to be recorded. When the laser turns on (when a 1 is sent to it) it burns a so called "pit" into the surface of the master. When it is turned off (when a 0 is sent to it) no pit is created. This area is called a "land". A number of glass masters are made from the first master, and these are used to duplicate (press) the finished product.

When the disc is played, a reading laser shines light onto the surface of the disc. The light takes longer to reflect from a pit than a land. This difference in the wavelength of the reflected light is recognised by the laser and a transducer converts the difference into an electrical digital pulse wave.

CD-R/RW and DVD-R/RW

CD-R/RW and DVD-R/RW work differently by using a laser to change the colour of a light sensitive dye which is spread across the surface of the disc. A reading laser differentiates between the wavelengths of the dyes to recover the 1s and 0s.

5. Radio signals sent over a wireless network

Binary 1s and 0s can be transmitted over a wireless network in the form of radio waves.

6. Optical signals

Binary 1s and 0s can be transmitted down an optical cable in the form of pulses of light.