RAM vs ROM
Two kinds of memory that get confused constantly. Learn the exact wording that earns the mark, find out what happens when RAM runs out, and place every kind of storage in order of speed.
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Why not just one memory?
Fast memory is expensive and small. Cheap memory is big and slow. No single technology is both, so a computer uses several kinds and moves data between them. Two of them sit on the main board and are called **primary storage**: **RAM**, which holds what the machine is working on right now, and **ROM**, which holds the instructions that get it started in the first place.
RAM against ROM
Each one is defined by TWO properties, and an answer that gives only one of them is not precise enough to score.
Which answer earns the mark?
A question asks you to state the difference between RAM and ROM. Which answer is precise enough?
- RAM is volatile and read-write; ROM is non-volatile and read-only
- RAM is temporary memory and ROM is permanent memory
- RAM can be written to and ROM cannot
- RAM is faster than ROM, which is why programs load into it
Match each memory to what it holds
- RAM
- ROM
- Cache
- Virtual memory
- The operating system, the programs open now and the data they are using
- The instructions that run the moment the machine is switched on
- Copies of the data and instructions the CPU keeps asking for
- Whatever had to be moved out of RAM onto secondary storage to make room
When RAM runs out
Open enough programs and RAM fills up. Rather than stopping, the operating system uses a section of **secondary storage** as if it were extra RAM. That section is called **virtual memory**. Data that is not needed right now is moved out there, and moved back when it is wanted again. It keeps the machine working, but it is much slower, because secondary storage is far slower than RAM and the swapping itself takes time. A computer that has run out of RAM and is relying heavily on virtual memory feels sluggish, and that is why.
True about virtual memory
Select the TWO statements that are true.
- It is a section of secondary storage being used as though it were RAM
- Relying on it heavily makes the computer slower, because of the speed of secondary storage and the cost of swapping data back and forth
- It makes the computer faster, because there is more memory available
- It is non-volatile, so open programs survive the power being cut
Primary storage in a paragraph
RAM is _____, so it loses its contents when the power goes off, and _____, so the computer can change what is in it. ROM is the opposite on both counts and holds the _____ instructions. When RAM fills up, the operating system uses _____ memory, a section of secondary storage, which keeps the machine going but makes it _____.
Fastest to slowest
Put these in order, starting with the fastest storage the CPU can reach.
- Registers, inside the CPU
- Cache
- RAM
- Virtual memory on secondary storage
Why does more RAM help?
A computer slows to a crawl whenever several programs are open. Fitting more RAM fixes it. Why?
- With more RAM the machine can hold everything it is running without falling back on virtual memory, so it stops swapping data to and from secondary storage
- Because adding RAM makes the RAM that was already fitted run faster
- Because the CPU runs at a higher clock speed when more RAM is available
- Because more of the operating system can be stored in ROM
Your turn: explain the memory
A friend says their laptop "has run out of memory" and asks whether buying a bigger hard disk would fix it. Explain what is actually happening and what would help.
- State what RAM is, using both of its defining properties
- Explain what the machine does when RAM fills up
- Explain why that makes it feel slow
- Say whether a bigger hard disk or more RAM is the right fix, and why