Primary Storage (Cambridge (CIE) O Level Computer Science)
Revision Note
Written by: James Woodhouse
Reviewed by: Lucy Kirkham
Primary Storage
Primary storage is directly accessed by the CPU
Computer systems need both primary and secondary storage to operate
Both types of storage play a crucial role in the operation of a computer system
A quick comparison of primary and secondary storage shows:
Primary | Secondary |
Volatile (with the exception of ROM) | Non-volatile |
Small capacity | Large capacity |
Why do you need primary storage?
A computer needs primary storage because access times are considerably faster than secondary
This means the time taken to complete operations such as the Fetch-Execute Cycle is dramatically reduced
Primary storage holds the data and instructions that the CPU needs to access whilst the computer is turned on
Due to the fast access times, primary storage is used as short-term, working memory, in hardware that is directly connected to the CPU such as RAM, and components that reside inside the CPU such as Cache and Registers
Performance of primary storage means a much higher cost which limits the amount that is used
For example, RAM is commonly purchased in 16 or 32 gigabytes whereas secondary storage such as a hard drive is in terabytes
RAM
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
Examiner Tips and Tricks
Just knowing what RAM is and what it stores is not enough, you must be able to apply your understanding of RAM to real world contexts where RAM is a component, e.g. TVs, game consoles and other smart devices
Worked Example
A smart television allows the user to search the Internet and watch videos online.
The smart television uses RAM
Give two examples of data that the smart television could store in RAM [2]
How to answer this question
Think about the main function of a smart television, watch channels, use apps to stream content and browse the web etc
For each function, try to think of what data would have to be in the RAM whilst you were actually doing it (in use!)
Possible answers
Current channel being watched
Current volume
Current video/file/tv program being watched
Web browser/applications that are running
Data being downloaded/buffered
Examiner Tips and Tricks
Examiners will accept anything reasonable when answering these style of questions BUT brand names will not be be awarded without giving an example
ROM
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
Examiner Tips and Tricks
RAM & ROM are examples of primary storage, they can be referred to as Main Memory or Primary Memory in the exam
Worked Example
Quinn has 512 kilobytes of ROM and 16 gigabytes of RAM in her computer
Describe the purpose of the ROM in Quinn's computer [2]
Describe the purpose of the RAM in Quinn's computer [2]
Answer
ROM
Store start-up instructions/bootstrap
Used to start the computer
RAM
Stores the parts of the OS / programs that are running
Stores data currently in use
...for access by the CPU
Guidance
Do not confuse the purpose with characteristics, describe what it does, not what it is
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