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!