Cambridge IGCSE Computer Science (0478) · lesson 18 of 35 · 20 min
RAM vs ROM
RAM in Detail
RAM is the computer’s working memory. When you open a program, it is loaded from secondary storage (SSD/HDD) into RAM so the CPU can access it quickly. RAM is volatile — all unsaved data is lost when power is removed.
Modern computers use DRAM (Dynamic RAM) for main memory — it is cheap and dense but must be refreshed thousands of times per second. The CPU’s cache uses SRAM (Static RAM) — faster and more reliable but more expensive.
ROM in Detail
ROM stores the firmware — the low-level software that runs when the computer first powers on (BIOS/UEFI). It performs the Power-On Self-Test (POST), initialises hardware, and loads the operating system from secondary storage into RAM.
Modern “ROM” is actually Flash memory (EEPROM) — it can be updated (firmware updates) but retains data without power.
Which type of memory loses its contents when the computer is switched off?
- ROM
- Flash memory
- RAM
- EEPROM
Answer: RAM
RAM is volatile — it requires power to retain data.
What is stored in ROM?
- The operating system
- User files
- Firmware/BIOS boot code
- Current running programs
Answer: Firmware/BIOS boot code
ROM stores firmware — the boot code that runs when the computer powers on.
Why is RAM used instead of secondary storage for running programs?
- RAM is cheaper
- RAM is non-volatile
- RAM is much faster to access
- RAM has more capacity
Answer: RAM is much faster to access
RAM access times are nanoseconds vs milliseconds for HDDs — orders of magnitude faster.
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