This bulletin’s theme is the physical storage components of your computers. It is a follow up to the previous bulletin.
In that previous bulletin, you learned that a computer processes information by passing electrical currents through carefully laid-out circuits of transistors. These electrical currents encode ones and zeros (think of it as there being a current versus there being no current).
In the processor, ones and zeros are represented as electrical current. But there are other ways ones and zeroes live in our computers.
On magnetic storage, the information is stored by setting the direction of magnetic field on a very small scale. It’s a bit like placing magnets in different directions in different boxes: magnets pointing this way mean zero, magnets pointing that way mean one. Instead of placing little magnets in boxes, the material itself is magnetised locally.
To read the information stored on the medium, simply detect the direction of the magnetic field. This is like placing a compass near a magnet and looking at the needle change direction, except this happens on a much smaller scale and there isn’t really a needle moving.
The material that is magnetised varies a lot.
- An iron coating on a thin strip of plastic makes a tape.
- A similar coating on a disk of plastic makes a floppy-disk.
- A similar coating on a disk of solid plastic, encased with its own reading apparatus makes a hard-disk drive.
With the invention of lasers, new technologies became possible: CDs, DVDs, BlueRay Disks, and other similar disks. In this technology, ones and zeroes are represented as little notches on a reflective surface. A laser bounces differently where there are notches from where there are none. And so reading information stored on the disk is as simple as shining a laser on the surface and checking where the reflected beam is.
There are variations between the different types of disks. For example, to read information on a BlueRay disk, you need a laser with a shorter wavelength (that’s a blue laser, hence the name). With a smaller wavelength, the reader can detect smaller notches, which allows us to store more information on a single disk.
When information is transmitted, for example when your computer loads emails from a server, it is transformed into different forms as well. For example, over WiFi, information is encoded as radio waves of specific frequencies: 2.4 GHz, 3.6 GHz, 4.9 GHz, 5 GHz, or 5.9 GHz.
For long distance transmissions, other electro-magnetic waves are used. For example, light in optical fibres. Because the optical fibre guides the light, energy does not disperse in every direction. This allows a longer reach. Additionally, the light does not interfere with other signals, which allows for higher bandwidth.
Other forms of information
There are other storage systems – e.g., USB thumbdrives and SSDs – and transmission methods, each with different tradeoffs. Some are cheap, some are expensive, some are light, some are heavy, some are resilient, some are fragile, etc. All store or transmit digitised information: information represented as ones and zeroes.