ROM RAM and Virtual Memory
Lesson Objective:Understand the difference between ROM, RAM and the purpose of Virtual Memory
Learning Outcome:Define the key words and give a brief explanation for each. Explain the workings of virtual memory
Keywords: ROM, RAM, Virtual memory, volatile, non-volatile
What is ROM?
ROM is Read Only Memory It does not need power to ‘remember’
so it is called non-volatile memory
It cannot change once written One purpose of ROM in a PC is to
store the boot sequence program to start the computer.
So what does ROM look like??
BIOS is an example of
ROM in a PC.
The program stored in ROM looks like this when it runs
If ROM doesn’t need power, why do we have a battery?
This is just one example of ROM used in IT. After the
data is written it cannot be changed or erased.
(Don’t get it mixed up with CD-RW)
(Not needed for the exam!)ROM, BIOS and CMOS
Some of the important settings of a computer needs to be changeable and
therefore needs to be held in RAM
This RAM is what needs the battery to ‘remember’ the settings. It uses a
power-efficient memory called CMOS(Complementary Metal Oxide
Semiconductor Field Effect Transistor)
The internal clock also needs power to hold the time and date (as does any
clock!)
What is RAM?
Random Access Memory It loses it’s memory when it has no
Power, therefore it is Volatile memory. The amount of RAM is important for the
speed of a computer. Some applications need more RAM than others.
So what does it look like?
RAM can be easily replaced on the
motherboard of a computer
How much RAM do you need?
Software usually comes with system requirements which
specifies the amount of RAM
needed as well as other
requirements. (Physical Memory =
RAM)
How much RAM? (Low, Medium, High, V. High)
Text editore.g. to write a short computer program.
Text editore.g. to write a short computer program.
Graphics editore.g. to edit a 5mb photo
Graphics editore.g. to edit a 5mb photo
LOW
Medium
How much RAM? (Low, Medium, High, V. High)
Computer game with animations
Computer game with animations
Video editore.g. to edit a 30 min
video
Video editore.g. to edit a 30 min
video
V. High
High /
V.High
How much RAM? (Low, Medium, High, V. High)
DTP software to make a 64 page magazine
DTP software to make a 64 page magazine
Database to store the addresses of every dwelling in London
Database to store the addresses of every dwelling in London
High
Medium
Word processor to write a letter
Word processor to write a letterLow
How much RAM? (Low, Medium, High, V. High)
Using RAM
What happens if there isn’t enough RAM to do everything?
0.5 GB
1 GB
1.5 GB
2 GB
Word Processor
Text editor
Video Editor
Database
Graphic Editor
Unused programs and data will move
to virtual memory
Unused programs and data will move
to virtual memory
Space is now available for
the new program and
data
Space is now available for
the new program and
data
RAMSuper- fast!
Virtual Memory- Setting aside space on a hard disk as RAM “overflow”
Virtual Memory (On Hard disk=slow)
10 GB
Programs are swapped in and
out of VM as needed.
Programs are swapped in and
out of VM as needed.
If there is not enough RAM for common use VM has to be constantly used and this SLOWS DOWN the performance of the computer.
Workbooks!