What is the difference between RAM and ROM?
Short answer
RAM (random access memory) is volatile: it holds the programs and data currently in use and loses everything when the power is turned off. ROM (read-only memory) is non-volatile: it keeps its contents without power and stores the start-up instructions (the BIOS or boot program). RAM can be read and written; ROM is normally only read.
Step by step
- Volatile or not: RAM loses data without power, ROM keeps it.
- Purpose: RAM stores the operating system, open programs and data in use; ROM stores the boot instructions.
- Read or write: RAM can be changed constantly; ROM is read-only in normal use.
- Size: RAM is usually measured in gigabytes; ROM is much smaller.
Worked example
What happens when you switch a computer on
- The CPU runs the boot program stored in ROM
- The boot program loads the operating system from storage into RAM
- You open apps, which are also loaded into RAM
Common mistakes
- Confusing RAM with storage. A hard drive or SSD stores files permanently; RAM is temporary.
- Saying ROM stores the operating system. It stores the instructions that load it.
- Saying more RAM makes the CPU faster. It lets more programs run without slowing down.
A one-to-one lesson with a tutor is the quickest way to fill the gaps before a test or exam. Your first lesson is free.
Find a Computer Science tutor