Cambridge A Level - Computer Science. Chapter 3 - 3.1.1 - Overview, Primary storage and embedded systems. (Suitable for IGCSE) Candidates should be able to: •Show understanding of the need for input, output, primary memory and secondary memory (including removable) storage. •Explain the differences between Random Access Memory (RAM) and Read Only Memory (ROM). •Including their use in a range of devices and systems and the reasons for using one instead of the other depending on the device and it