RAM and ROM: what's different and who uses which

By the end of this lesson

By the end you can explain the differences between RAM and ROM, and explain why a device uses each one for the job it does.

The notebook and the instruction manual

RAM is a scribbling notebook: you write, rub out and rewrite all day, and it's wiped every night.

ROM is the instruction manual glued inside the lid: always there when you open the box, and you can't (easily) change it.

	RAM (random access memory)	ROM (read-only memory)
Volatile?	volatile: lost when power is off	non-volatile: kept with no power
Read or write?	read and write	read only (contents fixed, or changed only by special means)
Holds	the OS, programs and data currently in use	start-up instructions (bootstrap loader), BIOS, firmware
Contents change?	constantly, while the device runs	not in normal use
Size in a PC	large (several GB)	small

Both are primary memory: the processor can access them directly.

At switch-on, RAM is empty. ROM is the only memory with instructions in it, so it has to go first.

Quick check

Multiple choiceQuestion 1 · Recall

Fill in the blanksQuestion 2 · Recall

Multiple choiceQuestion 3 · Apply

Answer the 3 questions above to continue.