Hardware · 4 question types
Past paper frequency (2018 to 2024)
This topic accounts for approximately 5% of your exam marks.
RAM vs ROM and primary vs secondary storage comparisons appear regularly.
The two primary-storage chips you must know are RAM and ROM.
RAM is primary storage that holds whatever data and instructions a running program needs right now. The CPU reads and writes RAM directly during the fetch-decode-execute cycle.
Key properties:
When you launch a program, its instructions are copied from secondary storage into RAM so the CPU can run them. When you save a file, the data is copied from RAM out to secondary storage so it survives the power being switched off.
ROM is primary storage that holds the very first instructions the computer needs at start-up, including the bootstrap loader and the BIOS.
Key properties:
ROM contains the bootstrap: the small program that runs the moment the computer is switched on. Its job is to test the hardware, find the operating system on secondary storage, and load enough of it into RAM for the system to take over. After that point, the running computer mostly uses RAM rather than ROM.
| Feature | RAM | ROM |
|---|---|---|
| Stands for | Random Access Memory | Read-Only Memory |
| Stores | Active program data and instructions | Bootstrap / BIOS / start-up instructions |
| Volatile? | Yes (lost when power is off) | No (kept when power is off) |
| Read/write? | Read and write | Read only (in basic ROM) |
| Speed | Very fast | Fast |
| Typical size | Many GB | Few hundred KB |