RAM, ROM, cache and virtual memory: what each holds, how fast it is and what happens when RAM runs out.
What you will learn
- Compare RAM and ROM
- Explain virtual memory and why it slows a computer
- Explain why more RAM can improve performance
- Trace a program through the fetch-execute cycle
Primary memory
| RAM | ROM | Cache | |
|---|---|---|---|
| Holds | programs and data in use now | the boot program (BIOS) | data and instructions used often |
| Volatile? | yes, lost when off | no | yes |
| Changes? | all the time | not in normal use | all the time |
| Speed | fast | fast | fastest |
Volatile means the contents are lost when the power goes off. Cache is faster than RAM because it is built from faster memory and sits on or very close to the CPU, but it holds much less.
Secondary storage (such as a hard disk or an SSD) keeps programs and data when the power is off. It is much slower than RAM, so programs are copied into RAM to be run.
The rest of this lesson and its 7 practice questions are locked.
In this lesson
- Primary memory
- Virtual memory
- Registers in action
- Try it: The accumulator
7 practice questions, marked as you go; about 20 minutes in all.
Key terms
Volatile, Secondary storage, Virtual memory
In this unit: Computer systems
The CPU and the fetch-execute cycle step by step, what makes a CPU fast, RAM, ROM and virtual memory, secondary storage, and system software.