Edexcel IGCSE ICT · Memory
RAM & ROM
Big idea: a computer needs two kinds of "quick-access" memory —
one that holds whatever you're doing right now and forgets it the moment
the power goes off (RAM), and one that permanently remembers how to switch itself
on in the first place (ROM).
Summary — the whole topic in one scan
- RAM = temporary, read/write, volatile working memory that holds data & programs currently in use.
- ROM = permanent, read-only, non-volatile memory that holds the boot instructions (including the BIOS).
- Both are types of primary storage — directly accessible to the CPU, unlike secondary storage (HDD/SSD).
- RAM is bigger in capacity and expandable; ROM is small, fixed, and can't be increased.
- Some ROM chips can be reprogrammed: EPROM and EEPROM.
- Flash memory is a type of EEPROM — non-volatile, fast, low power, used in SSDs, USB sticks, and SD cards.
- Less RAM → more reliance on slower secondary storage/virtual memory → slower performance.
1. RAM (Random Access Memory)
What is RAM, really?
RAM is primary storage that sits directly connected to the CPU. Think of it as the
computer's short-term working memory — the desk you're working at, not the filing
cabinet in the next room. Whatever the CPU is actively using right now — the app you have open,
the document you're editing, the game you're playing — gets loaded into RAM so the CPU can grab it
instantly, instead of having to fetch it from slow secondary storage every single time.
Analogy: imagine you're doing homework at your desk. Your desk (RAM) can only hold
the books and papers you're actively using right now. Your bookshelf across the room (secondary
storage — the hard drive/SSD) holds everything you own, but it takes time to walk over, find a
book, and bring it back. The bigger your desk, the more books you can have open at once without
constantly walking back and forth — that's exactly why more RAM = smoother multitasking.
Key properties of RAM
- Volatile — its contents are lost the instant the power is turned off. This is the single most important fact about RAM. Nothing is saved permanently in RAM.
- Temporary — it only holds data & instructions that are currently in use.
- Copied from secondary storage — for the CPU to work with something, it must first be copied out of secondary storage (HDD/SSD) into RAM.
- Very fast — much faster than secondary storage, though slightly slower than the CPU's own internal cache/registers.
- Read/write — data can be both read from RAM and written to it. This is different from ROM.
- Large, variable capacity — modern computers typically have several GB of RAM, and unlike ROM, you can usually add more RAM to boost performance.
Core rule to remember
RAM = Read/Write + Volatile + Temporary + Large + Directly connected to CPU.
Why does volatility matter in real life?
This is exactly why your computer nags you to "save your work" — if you lose power or the app
crashes before you hit save, whatever was only sitting in RAM (your unsaved changes) is gone
forever. Saving copies it from RAM into secondary storage, which doesn't lose data when
the power goes off.
2. ROM (Read Only Memory)
What is ROM, really?
primary storage