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AS · Practice questions · RAM and ROM: SRAM, DRAM, PROM, EPROM and EEPROM

Volatile or not.

Six original Cambridge-style questions on primary memory: RAM and ROM, SRAM and DRAM, and PROM, EPROM and EEPROM, with mark-scheme style solutions.

Original questions All questions on this page are original work, written in the Cambridge AS & A Level style. They are not from past papers. They test the same concepts and skills the syllabus rewards.
Keep these straight

One difference explains the rest.

01
Recall
[3 marks]

State three differences between RAM and ROM.

  • RAM is volatile; ROM is non-volatile. ✓
  • RAM can be read and written; ROM can only be read (in normal use). ✓
  • RAM holds the programs and data currently in use; ROM holds the bootstrap program or firmware. (Or: RAM is usually much larger than ROM.) ✓
02
Explain
[4 marks]

Explain the differences between static RAM (SRAM) and dynamic RAM (DRAM).

  • DRAM stores each bit as charge on a capacitor; SRAM stores each bit in a flip-flop. ✓
  • DRAM must be refreshed constantly because the charge leaks; SRAM does not need refreshing. ✓
  • SRAM has a faster access time than DRAM. ✓
  • DRAM is cheaper per bit and has a higher density (more data per chip). ✓
03
Apply
[4 marks]

A games console has 16 GiB of main memory and a processor with 32 MiB of cache. Identify the type of RAM used for each and justify your choices.

  • Main memory: DRAM. ✓
  • A large capacity is needed at a reasonable cost, and DRAM is cheaper per bit and denser. ✓
  • Cache: SRAM. ✓
  • Cache must be very fast to keep up with the processor, and only a small amount is needed, so the higher cost is acceptable. ✓
04
Explain
[3 marks]

Describe how PROM, EPROM and EEPROM differ in the way their contents can be changed.

  • PROM can be programmed only once (fuses are blown); its contents can never be changed. ✓
  • EPROM can be erased by exposing it to ultraviolet light (whole chip, removed from the device) and then reprogrammed. ✓
  • EEPROM can be erased and reprogrammed electrically while still in the circuit (byte by byte). ✓
05
Apply
[2 marks]

A digital thermostat must remember the user's chosen temperature when the power is cut. The setting may be changed many times. Identify a suitable type of memory and give a reason.

  • EEPROM (or flash memory). ✓
  • It is non-volatile, so the setting is kept without power, and it can be rewritten electrically in place each time the user changes it. ✓
06
Analysis
[2 marks]

A student writes: "SRAM is called static because it keeps its data when the computer is switched off." Explain the error.

  • SRAM is volatile: it loses its data when the power is switched off. ✓
  • Static means it does not need to be refreshed while the power is on (unlike dynamic RAM). ✓

Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.