Memory and Storage
Primary storage
- RAM – holds programs/data currently in use. Volatile (lost when off). Read and write.
- ROM – holds boot/start-up instructions. Non-volatile, read-only.
- Cache – very fast memory between CPU and RAM.
- Virtual memory – uses part of the hard disk as extra "RAM" when RAM is full (slower, because the disk is slower).
Secondary storage (non-volatile, long-term)
| Type | Examples | Notes |
|---|---|---|
| Magnetic | HDD | Cheap, large capacity, moving parts, less durable |
| Solid state | SSD, USB | Fast, durable, silent, no moving parts, pricier per GB |
| Optical | CD/DVD/Blu-ray | Cheap, low capacity, portable |
Choosing storage — factors
Capacity · Speed · Portability · Durability · Cost · Reliability.
Example: a phone uses solid state (small, durable, fast, no moving parts).
Exam tip
"Why does a computer need secondary storage?" → because RAM is volatile, so data must be stored permanently elsewhere. SSD vs HDD comparisons are common — know the trade-offs.