Cambridge IGCSE 0478 · Topic 3 · 3.3

Data
Storage

Primary Memory · Secondary Storage · RAM · ROM · HDD · SSD · Optical · Flash

CSZoneCambridge IGCSE Computer Science 0478

Primary Memory

RAM and ROM

RAM (Random Access Memory): volatile — loses contents when power is off. Stores data and programs currently in use. Faster access than secondary storage.

ROM (Read Only Memory): non-volatile — contents are permanent. Stores the boot program (BIOS/UEFI). Cannot be written by normal programs.

More RAM = more programs can run simultaneously without slowing down

Secondary Storage

HDD, SSD, Optical & Flash

HDD (Hard Disk Drive): magnetic spinning platters. Large capacity, cheap per GB. Fragile; slower than SSD. Good for bulk storage.

SSD (Solid State Drive): NAND flash memory chips. Very fast, no moving parts, silent, durable. More expensive per GB than HDD.

Optical disc (CD/DVD/Blu-ray): laser read/write. Portable, cheap. Used for distribution of software/films; slower than HDD.

Flash/USB drives: portable, no moving parts, convenient. Lower capacity than HDD but very portable.

Virtual Memory & Cloud Storage

Extending Storage

Virtual memory: when RAM is full, the OS uses part of the HDD/SSD as temporary RAM. Slower than real RAM but prevents crashes. Page swapping = moving data between RAM and virtual memory.

Cloud storage: data stored on remote servers accessed via internet (e.g. Google Drive, Dropbox). Accessible anywhere, but requires internet connection; privacy/security concerns.

Exam Practice

Have a go at this question

Cambridge IGCSE 0478 style

State two differences between RAM and ROM.

4 marks

RAM is volatile (loses data when power is removed) [1] whereas ROM is non-volatile (data is permanently stored) [1]. RAM can be read from and written to [1] whereas ROM can only be read from under normal operation [1].

Key Takeaways

What to Remember

RAM: volatile, read/write, stores running programs; ROM: non-volatile, stores boot code

HDD: cheap, large, magnetic, fragile; SSD: fast, no moving parts, more expensive

Optical: portable, cheap, used for distribution; Flash: portable, convenient

Virtual memory: HDD used as RAM when RAM is full; cloud: remote, accessible anywhere