Memory Types (Cambridge (CIE) A Level Computer Science): Revision Note
Exam code: 9618
RAM vs ROM
What is RAM?
RAM (Random Access Memory) is primary storage that is directly connected to the CPU and holds the data and instructions that are currently in use
RAM is volatile which means the contents of RAM are lost when the power is turned off
For the CPU to access the data and instructions they must be copied from secondary storage
RAM is very fast working memory, much faster than secondary storage
RAM is read/write which means data can be read from and written to
In comparison to ROM, it has a much larger capacity
What is ROM?
ROM (Read Only Memory) is primary storage that holds the first instructions a computer needs to start up (Bootstrap)
ROM contains the BIOS (Basic Input Output System)
ROM is a small memory chip located on the computers motherboard
ROM is fast memory, much faster than secondary storage but slower than RAM
ROM is non-volatile which means the contents of ROM are not lost when the power is turned off
ROM is read only which means data can only be read from
In comparison to RAM, it has a much smaller capacity
Differences between RAM & ROM
Feature | RAM | ROM |
|---|---|---|
Speed | Very fast | Fast (slower than RAM) |
Capacity | Gigabytes (GB) | Megabytes (MB) |
Stores | Programs and data in use | Bootstrap (start-up instructions) |
Read/Write | Read & write | Read only |
Volatile/Non-volatile | Volatile | Non-volatile |
SRAM vs DRAM
What is SRAM?
SRAM (Static RAM) is a form of RAM that keeps data as long as power is on
SRAM is made from flip-flops so there is no need for constant refreshing
SRAM is used in places where speed is more important than storage size
An example of where SRAM is used is:
Cache memory, where quick access to data is most important
Very fast – faster than DRAM
Uses less power, good for low-power devices
Expensive to make
Takes up more space – lower storage capacity compared to DRAM
What is DRAM?
DRAM (Dynamic RAM) is a form of RAM that stores each bit in a tiny capacitor
DRAM needs constant refreshing to keep the data
DRAM is commonly used as:
Main memory (RAM), where larger amounts of cheaper storage is required
Cheaper to produce than SRAM
Higher capacity – can fit more memory in less space
Slower than SRAM, needs time to refresh data
Uses more power, especially during refreshing cycles
PROM vs EPROM vs EEPROM
What is PROM, EPROM & EEPROM?
PROM, EPROM and EEPROM are all types of ROM that are programmed and reprogrammed in different ways
Each type has a specific application in difference devices
Feature | PROM | EPROM | EEPROM |
|---|---|---|---|
Can be reprogrammed? | No – programmed once only | Yes – can be erased and rewritten | Yes – can be erased and rewritten |
Erased using | Cannot be erased | UV light | Electric voltage |
Must be removed from device? | No | Yes – must be removed from the device | No – can be erased in place |
Erased all at once? | Not applicable | Yes – entire chip is erased | No – specific parts can be erased |
Common use | Permanent firmware | Reprogrammable chip development | Flash memory, BIOS chips |
Examples | Remote controls, basic calculators, early model washing machines | Arcade machines (older models) Early games consoles | BIOS chips in computers, Smart cards, remote key fobs, flash memory like USB sticks and SSDs |
Worked Example
A computer has hardware and software.
The hardware includes different types of memory.
Complete the description of computer memory. [5]
Random Access Memory (RAM) and Read Only Memory (ROM) are both examples of ......................................................................... memory.
One item that is stored in RAM is ......................................................................... . One item that is stored in ROM is ......................................................................... . RAM can be either Static RAM (SRAM) or Dynamic RAM (DRAM).
SRAM uses transistors arranged as ......................................................................... . DRAM uses transistors and .....................
Answer
Random Access Memory (RAM) and Read Only Memory (ROM) are both examples of primary memory.
One item that is stored in RAM is currently running software/data/part of the OS.
One item that is stored in ROM is the start-up/boot-up instructions/BIOS.
RAM can be either Static RAM (SRAM) or Dynamic RAM (DRAM).
SRAM uses transistors arranged as flip-flops.
DRAM uses transistors and capacitors.
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