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Describe the purpose of the CPU
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Understand how ROM, RAM, I/O, storage link to CPU
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Explain performance of CPU – looking at clock speed, cores & cache
 The CPU (Central Processing Unit) is hardware that executes programs and manages
the rest of the computer system. It sits underneath the heat sink on the
motherboard and is made up of millions of electrical switches called transistors.
 All data is stored within a computer as electronic signals in micro-circuits. There are
only 2 types of signal –on or off. A micro-circuit can either carry an electrical signal
or not. This will lead to our discussion of binary later in the course.
 The CPU is often known as the “brains” of the computer and its purpose is to process
data. It does this by performing functions such as calculating, decision making and
moving data around.
 Our computers would not work if not for the CPU, similar to us not functioning
without our brain!
 Think of all the tasks our computer does. Write a list of 10 jobs.
 Eg. Perform a function on a spreadsheet…
 …the CPU will deal with all the data processing, without it none of your tasks will be
performed.
 The first CPU chip was invented in 1971 – a 4 bit processor designed for a calculator! This
is where our story starts…
 Processor speed has doubled over time while a second processor has resulted in the phrase
dual-core which is a double processor – doubling the speed.
 It doesn’t stop there, quad-core, hexa-core and octa-core offer the next steps to power
our machines even faster.
 Software running on our systems have to be designed to take full advantage of all these
new progressions.
 Current mobile devices will carry mobile processors; small versions without fans to keep it
cool.
•You input information and commands using
the mouse and keyboard.
•You see/hear the results on the output devicesscreen and speakers
•The CPU ("processor") is the working brain of
the computer, that does all the processing and
computation
•The memory ("RAM") is where the CPU keeps
information it is working with (the information in
the RAM is lost when the computer is switched
off)
•Storage (e.g. hard-disks, USB data sticks) is
where the computer keeps information for longer
periods (not lost when the computer is off)
 The CPU consists of 3 major components:
 The Arithmetic and Logic Unit (ALU)
 The Memory Unit
 The Control Unit (CU)
 The ALU – carries out mathematical tasks rapidly, performs
calculations and logic operations in binary form 1/0 on data from the
memory unit. The ALU transforms the digital data and outputs the
resulting value.
 The Memory Unit consists of a small number of memory registers
which will store items of data and send them to the ALU for
processing. The result of the processing will be copied back to the
memory unit for storage.
 The CU – is in charge of processing. It interprets the software
instruction and sends the right data and operation to the ALU. It
accepts the result of the processing from the ALU and sends it back to
the memory unit. The CU will keep track of the sequence of
instructions and the location of each item of data and software
instruction in the memory unit.
 It runs a computer program
 What is a program?
 Program : the sequence of instructions stored in ‘memory’ required to solve a specified problem
 Computer architecture:
Fetch : read instruction from cook book.
Decode : understand instruction and get ingredients from store
Execute : crack egg into bowl.
 The CPU will typically perform the following
execution cycle:
 The CU fetches a single instruction and data from
the main memory
 The instruction is decoded.
 The ALU executes the instruction
 The ALU sends the result of the processing back to
the control unit – this is stored in the memory unit.
 Just how does the CPU interact with the rest
of the system?
 A bus or a cable (a collection of fine wires)
 The System Bus is a major component of a
computer:
 Data Bus: Carries the data that needs processing
 Address Bus: Determines where data should be
sent
 Control Bus: Determines data processing
 ROM & RAM are memory areas that are closely linked to the CPU.
 RAM is the type of memory used in the computer’s main memory.
 RAM is the active memory of the computer. The contents of all open software applications and
data files are held in RAM.
 So when a program is running it has to be loaded from the hard disk into the main memory so
the processor can access the instructions.
 RAM acts as temporary storage for programs and data just while it is running. This makes it
volatile.
 Once the program has finished and closed it is no longer main memory.
 ROM is Read Only Memory – you can not write over the contents once it has been created. This
makes it non-volatile.
 More on ROM & RAM later in the course…
 The power and speed of a computer is limited by the speed with which the computer
can carry out the fetch-execute cycle.
 Computers can only process one instruction at a time.
 If you are running many programmes eg. Surfing the net, working on an essay,
listening to music and sending an e-mail all at the same time (multi-tasking) it may
seem that the computer is processing all these tasks simultaneously.
 In reality it is handling one instruction at a time but it does it rapidly!
 The amount of time the CPU has to process each instruction is controlled by a quartz
clock, with every tick the CPU is able to process one piece of data or execute one
instruction.
 The CPU clock speed is measured in cycles per second. 1 cycle peer second is known
as 1 Hertz.
 A computer running at 1GHz can carry out a thousand million instructions per second.
 So the speed of the clock determines the basic performance of the CPU – the faster it
goes, the more powerful the computer.
 If the CPU has more than one core, it can execute more than one instruction.
 Cache memory is memory that can be accessed
rapidly by the processor. It holds a copy of the data
that is stored elsewhere.
 If the processor has to access main memory less
often it can work faster so the CPU performs better.
 The data that the computer needs right away is
taken from storage before processing begins and
kept in cache memory while it is in use.
 There are several types of cache:
 The memory register is very small cache, it holds data
for immediate use.
 L1 cache is small, fast and expensive
 L2 cache is larger but slower
 In programming a cache library can be used for
storing database queries for later use.
CPU
The central processing unit of a computer. Hardware that executes programs and manages
the system
ALU
The arithmetic and logic unit. Part of the CPU where data transformation occurs. It
operates electronically.
Fetch-Execute A single operation of the CPU: a stored instruction is taken from memory, carried out and
Cycle
the resulting value stored to memory.
Dual-Core
Processor
A CPU with 2 processing components to speed up tasks
Cache Memory Acts as a buffer between main memory and the CPU – “fast memory”
ROM
Read Only Memory – Not Volatile
RAM
Random Access Memory - Volatile
Fill in the blanks with the given words
NAME: ______________