Primary and secondary storage
Memory and storage
- Primary storage (RAM and ROM) is memory the CPU uses directly.
- Secondary storage keeps data permanently, even with the power off.
- When RAM is full, virtual memory helps.
RAM vs ROM
- RAM (random access memory) — read and write, volatile (loses data without power); holds the programs and data in use now.
- ROM (read-only memory) — read only, non-volatile (keeps data without power); holds the start-up instructions.
- Both are needed: ROM starts the computer, then RAM holds what you run.
Practice
Which statement is true?
RAM loses data without power (volatile); ROM keeps it (non-volatile) and holds start-up instructions.
Practice
ROM typically stores:
ROM is non-volatile and holds the boot instructions; running programs live in RAM.
Secondary storage
- Magnetic — magnetised spots on spinning disks (HDD, tape).
- Optical — marks read by a laser (CD, DVD, Blu-ray).
- Solid-state — flash memory, no moving parts (SSD, USB drive, memory card).
- All are non-volatile and used for long-term storage.
Practice
Match each secondary-storage type to an example.
Magnetic = spinning disks; optical = laser-read discs; solid-state = flash, no moving parts.
Practice
A solid-state drive (SSD) stores data:
SSDs use flash memory and have no moving parts — faster and tougher than a hard disk.
Virtual memory
- When RAM is full, the computer uses part of the secondary storage as extra, pretend RAM — virtual memory.
- Data not needed right now is moved to the disk, freeing RAM for other programs.
- This lets you run more programs than RAM alone could hold, but it is slower (disk is much slower than RAM).
Practice
Virtual memory is:
When RAM fills up, the OS moves idle data to disk to free RAM — slower, but it lets more programs run.
You've got it
Key idea
- RAM = volatile, read/write, programs in use; ROM = non-volatile, read-only, start-up
- secondary storage: magnetic (HDD), optical (CD/DVD), solid-state (SSD/flash)
- all secondary storage is non-volatile
- virtual memory uses disk as extra RAM — lets more programs run, but slower