Memory Unit Two – Computing Science OCR GCSE

Memory: (where binary data (in 0s and 1s) is stored)

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RAM – random access memory

ROM – read only memory

Difference between RAM and ROM:

RAM ROM
-stores programs that are currently in use ROM is a special memory chip that can store data even without power. It is non-volatile.
-helps to allow multi-tasking ROM is used by a computer to store the boot sequence instructions. This is everything the computer needs to boot and load the operating system.
-stores all the instructions/modules from the open programs that the CPU will require for processing Data on ROM is permanently written
-stores data as small charges of electricity in tiny transistors engraved into a circuit in the device When you switch on your computer, data in the ROM is accessed by the CPU in order to start the computer and load the operating system successfully.
-RAM is volatile – it loses its data when there is no power Data is pre-written and comes with the computer
-When programs are opened by the user, they are loaded from secondary storage onto the RAM. This is so that the CPU can access the data and instructions at a quicker rate. This is because if the CPU reads the program instruction and data from secondary storage then the data access would be extremely slow. This is why RAM is so important.
Data is not permanently written to this type of memory
Computer needs to be on to retain data

 

Purpose of RAM:

Stores data that is currently in use so it can be accessed quickly by the device’s processor.

Purpose of ROM:

-Stores the boot instructions of the computer that allows the CPU to access to start the computer.

Virtual Memory: This is when secondary storage is used as if it was RAM.

The need for virtual memory:

When the RAM is overloaded/full, the computer needs to relocate programs that not have been recently used to the secondary storage. This process takes time as secondary storage data speeds are much slower. However, when it is done, the system should perform a lot faster.

 

Flash Memory:

Flash memory is usually based on a technology called Electrically Erasable Programmable Read-Only Memory.

Flash memory is used in:

Solid State Drives – a form of re-writable flash storage

Secure Digital Cards (SD) – Used to extend the capacity of devices; cameras, phones. They provide high capacity for their physical size, this is useful in smaller devices.

ROM chips – Provides the software needed for the computer to start.

Properties:

-Short lifetime – flash memory can only be flashed (re-written) a certain number of time before it starts to degrade

-robust – not easily damaged by shocks

-non-volatile – it will keep its contents once power is switched off.

-fast access – faster access to data than many other storage media due to no moving parts

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