1. Memory
Miss Elliott

2. What is memory?
What is ROM and RAM?

3. 5 mins
ROM and RAM
The main internal memory in a computer can be split into two types:
ROM (Read Only Memory)
RAM (Random Access Memory)

4. ROM
As the name (Read Only Memory) suggests, this memory that cannot be changed by a program or user.
It is used to store the instructions for the computer to start up when it is turned on again.
The data in the ROM is saved even if the computer is switched off and this is known as “non-volatile” data.

5. RAM
RAM is much faster than ROM and is used as a temporary memory in which programs, applications and data are stored whilst they are being used.
If a computer loses power, all data stored in its RAM is lost, this is known as “Volatile” data.
Secondary Storage
RAM
Cache Memory
CPU

6. MEMORY
Size of Cache
The more cache memory there is, the more likely that the data will have already been requested from the main memory and placed into the cache. Therefore, it is less likely it will have to be retrieved from the main memory so the CPU can run faster.
The cache memory is very fast but also very expensive so it is a lot smaller than the main memory in a computer.

7. Levels of Cache Generally there are three levels of cache memory:
This is usually located on the CPU chip itself but has a very low capacity and runs at the same speed as the CPU.
Level 2
This is a little further away from the CPU and is larger but slower than the CPU.
Level 3
This is the largest of the three levels but also the furthest away and therefore the slowest.

8. Flash Memory
ROM uses a similar group of transistors wired together to make a circuit that are programmed with the instructions to boot up the machine at the point of manufacture.
These circuits trap electrons in the transistors using a large “flash” of electrical charge. This is where it gets its name from.
It is the same technology used in removable storage devices such as a USB memory stick.

9. Flash Memory
Remember: ROM stands for Read Only Memory and is used for the instructions used to boot up the computer.
Flash memory sticks are used to write and re-write files time and time again and this writing and re-writing can cause the circuits to deteriorate over time so flash memory sticks should not be used in critical systems.

10. Virtual Memory
Virtual memory is a feature of an operating system (OS) that allows a computer to compensate for shortages of physical memory by temporarily transferring pages of data from random access memory (RAM) to disk storage.

11. Virtual Memory
Primary memory has a limit i.e how many RAM chips you have in the computer. But there is a trick that the memory manager can use to fool the operating system into thinking that there is more primary memory than is actually physically present. This trick is called virtual memory.
When the computer is running short of physical primary memory e.g. too many applications open, the memory manager has a choice. It can either shut down applications (very inconvenient) or it can try and scrounge some more memory from somewhere else. This is where virtual memory comes in.

12. Exam Style Questions Describe the difference between RAM and ROM
Explain the need for ROM in a computer system
Describe the purpose of RAM in a computer system
Explain how the amount of RAM in a personal computer affects the performance of the
computer
Explain the need for virtual memory
Describe cache memory
Describe flash memory