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CPU, RAM and ROM
Lesson Objective:
Understand the main function of the CPU,
ROM and RAM in a computer
Learning Outcome:
Answer the questions on the worksheet
Question
 What’s the point of today’s lesson?
What does ‘CPU’ mean?
 Central Processing Unit
What does the CPU do?
 It is the hardware which makes the
whole computer system work.
How does it work?
THE CPU
I
N
P
U
T
Keyboard, mouse,
software programs
Control Unit
Arithmetic and Logic Unit
Immediate Access Store
O
U
T
P
U
T
Monitor, printers … etc.
BACKING STORE
Hard disk, RAM, etc.
Control Unit
 Control Unit – Makes the system work
 Coordinates the hardware connections
 Controls input, output and flow of data
through control signals
Arithmetic and Logic Unit
Is Profit < 0?
Yes
No
 Arithmetic Logic Unit – Data processing
 Makes calculations (arithmetic functions)
 Makes logical decisions
Immediate Access Store
 Work space and Data Store
 Holds data which is active
 Low capacity but very fast
What does each part do?
 Control Unit – Makes the system work
 Coordinates the hardware connections
 Controls input, output and flow of data
 Arithmetic Logic Unit – Data processing
 Makes calculations (arithmetic functions)
 Makes logical decisions
 Immediate access store – Data Store
 Holds data which is active
 Low capacity but very fast
Draw the CPU on your
worksheet
 Include the following parts:






Input
Output
Control Unit
ALU
IAS
Backing Store
CPU Specification
 The specification informs you of the
power and speed of the processor.
Intel® Celeron® 450 Processor (2.2GHz,512k cache)
Intel Core 2 Duo E7500 (2.93GHz,3MB cache)
ROM
 ROM stores data but unlike RAM it is
‘locked’- it cannot be written to.
 It is typically used to store small
amounts of important information used
when a computer is started.
 On power-off ROM does not lose its data,
it is Non-Volatile (RAM is Volatile)
Typical use for ROM
 The main functions of a
Mobile Phone are usually
held in ROM- the
program is not lost when
you switch the power off,
but neither can it be
changed.