iGCSE Computer Science - Distance Learning

Tutor Marked Assignment 6
Tutor Marked Assignment 8 (Programming)

Secondary Storage

We know that memory is always internal to the computer, but storage can be either secondary or offline.

When we discuss memory and storage, it is important to make a distinction between three different types of memory and storage : primary, secondary, and offline.

Primary memory (sometimes referred to as just memory) is used for running the computer system and includes components such as RAM, ROM, and cache. This memory is always internal to the computer system and is not removable on a regular basis.

We can classify storage in several different ways. The first way is to identify where about in the computer system storage belongs, and then its overall purpose. Storage can be classified as secondary or offline.

Secondary storage refers to the internal storage devices within the computer system. This often refers to the hard drive where the computer systems operating system and programs are stored whilst not in use. Often secondary storage will have a greater capacity than offline storage as it is required to store the main system data.

Lesson Task

Watch the video below and create a comparrison table to consider the difference between an SSD and HDD. Use this to write a short report on which you would recommend to a friend building a new computer system.

Finally, offline storage can vary depending on its purpose. The reason for having offline (external) storage may range from creating a backup that can be taken to a different physical location, to transporting a small number of files to a different device. It is possible to buy hard drives what are external to the computer system providing an external storage device with a greater capacity. However, due to the potential for damaged during transport it is not advised to use these devices for permanent storage of data. Other examples of external storage are SD cards, USB memory sticks, and discs.

When looking at storage, we often categorise them further by the way that they store the data. There are 3 main ways that data can be stored: magnetic, solid state, and optical.

Magnetic Storage

Magnetic storage saves data by creating a positive or negative polarised charge on a magnetic surface. This was one of the first methods of storing data when files were stored on floppy disks and tapes. Magnetic storage is red by passing the tape or disc surface over read head which identifies whether that point in the surface holds either positive or negative charge and converts this into the ones and zeros of binary.

Hard disk drives contain discs known as platters which are used to store magnetic data. Because these platters looked like discs it is easy to mistake hard disk drives as optical storage when in fact they are magnetic. It is for this reason that it is not advised to place a hard disk drive close to a strong magnet as the data may become corrupted.

Solid State Storage

Solid state drives are much newer technology and allow they need to be saved unread without the need for any moving parts as they use computer chips to store the data in the same way but the ram inside the computer stores data temporarily. this much newer technology is known as flash memory comma and although it uses the word memory it is in fact storage. It is entirely likely but you have already used a form of solid state storage , especially if you transport your files using a USB memory stick Oh have an SD card inside your smartphone or Camera.

One benefit of using solid state over the older magnetic storage is that it is much faster to access the data and because there are fewer moving parts it is also more energy efficient.

Optical Storage

Finally, optical storage is and storage media that is read using a laser. Discs such as CDs, DVDs comma and Blu Rays are all forms of optical storage and he is different types of laser to read the data that is written on them. Because of the technology that is used to read the discs, drives that can read the newer forms of disc are backwards compatible. However, older drives are not forwards compatible, and the reason for this is because of the type of laser that is used to read the disc.

When data is written onto an optical disc it is written using the spiral that goes from the centre of the disc to the outside known as a track. This track needs to be wide enough for the laser to read the data which is written using pits and lands (the pits being dents in the disc or darker areas for rewritable discs). When the laser is shone onto the disc these areas reflect the light back differently allowing the device to read either a one or a zero.

The reason why optical storage is not forwards compatible is to do with the colour spectrum which you may have come across in your physics lessons.

CDs are read using a red laser which has a wider beam than other colours meaning that the track has to also be wider. DVDs are read with an orange laser – because an orange laser is thinner the track can also be thinner which means that the spiral can be tighter and more data stored on the desk. This is true again for Blu Rays which use a blue laser which is on the other end of the colour spectrum and much thinner allowing for a much thinner track which allows far more data to be stored on a disc of the same physical size.

Comparison CD DVD HDDVD BD

Revision Task

Download, print, and complete the revision notes below. Don’t forget to add colour to key terms and add your own notes in the spaces provided.