Systems
Architecture
Friday, 27 April 2018
Systems Architecture
Today’s Objectives:
1. To be able to explain the purposes and uses of embedded systems.
2. To be able to describe how the CPU executes instructions and the
stages of the fetch-decode-execute cycle.
3. To be able to describe the purpose and functions of the CPU and
the different components.
4. To be able to explain how the characteristics of a CPU affects their
performance.
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– Systems Architecture
Today’s Key Terms: Hardware, devices, embedded systems, processing,
Firmware, microchip, U, components, functions, ALU, CU, MAR, MDR,
Processor, CPU, MHz, GHz, Hertz, instruction, clock speed, cache, core,
Moore’s Law.
Embedded
Systems
Types of Computers
All computers can be classified into two different groups:
• General purpose systems
• Embedded systems
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– Systems Architecture
General Purpose System
A general purpose computer can perform many different tasks.
Examples of General purpose systems are:
• Personal computers
• Laptops
• Tablets
• Smart phones
To perform a range of tasks they use software applications.
For example, a tablet can be used to listen to music, view web
pages, use camera software and create documents
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– Systems Architecture
Embedded Systems
• An embedded system is a computer which performs one specific
task within a larger mechanical system.
• Embedded systems do not look like a traditional computer. They do
not have a monitor, keyboard or touch screen.
• They are built on a single printed circuit board.
• They are made up of both hardware and the software that they
specifically need to do their task. This is known as ‘Firmware’
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– Systems Architecture
The CPU
CPU
Defined…
• The purpose of the CPU is to process data.
• It is where all the sorting, searching, calculating and decision making
takes place
The CPU:
• Fetches instructions from memory (RAM)
• It decodes those instructions
• It then executes (carries out) the instructions.
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– Systems Architecture
CPU
• As well as processing data, the CPU also controls the computer
hardware, for example the:
• Hard disk
• Input/output devices
• DVD drive
• Sound system
• Graphics system
This is done in conjunction with
the computer’s operating
system.
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– Systems Architecture
CPU – In diagram form
The main components of the
CPU you need to know about
are:
• The Control Unit (CU)
• The Arithmetic Logic Unit
(ALU)
• The registers
• The cache
• The clock
• The data buses
Also known as the “Von Neumann
Architecture”
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– Systems Architecture
The Control Unit (CU)
The control unit coordinates the actions of the computer. Sending
out control signals to the other parts of the CPU such as the ALU and
registers. It also controls the other components of the computer
system such as the input and output devices.
The two main elements of the control unit are the clock and the
decoder.
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– Systems Architecture
The Clock & Decoder
• Pulses are sent out to components to coordinated their activities The
timing is controlled by a tiny vibrating quartz crystal.
• Each time the clock ticks the CPU can process one instruction (Higher the
clock speed the more process that can be completed)
• Clock speed is measured in cycles per second. A typical clock has a
speed of around 3GHz which means the CPU can carry out three
thousand million instructions per second!
• The decoder is the section of the control unit that decodes the program
instructions brought from the memory and decides upon their action.
Cycles per second
Rate
1
1 Hertz
1 million
1 megahertz (MHz)
1,000,000,000
1 gigahertz
(GHz)
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– Systems Architecture
Clock Speed
• Each time the clock ticks, one complete fetch-decode-execute cycle
will take place.
• This means that during each tick, a single instruction will be processed.
• The higher the clock frequency, the faster the CPU can run.
• And the faster the CPU runs, the more instructions that can be processed
every second.
• Increased speed has limitations:
• Instructions are processed by transistors. The rate
at which they work has not become faster.
• Large amounts of heat are generated, increasing as
the clock speed does. Heatsinks & fans are used but
these have limited rates of cooling
• Clock speeds of 9 GHz require cooling by liquid nitrogen
Heatsink
Fan
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– Systems Architecture
Overclocking
• The CPU clock speed can be increased beyond the normal design limit.
This allows the CPU to process more instructions per second.
• This is called ‘overclocking’. It is something gamers like to do with their
machines.
• But to overclock, you will need a very good cooling system to stop the
CPU from overheating.
Hea tsink
Fan
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– Systems Architecture
What is it?
The Arithmetic and Logic Unit (ALU)
The ALU handles the data processing inside the CPU
• It performs standard arithmetic operations such as:
• addition and subtraction
• multiplication and division
• It deals with logic – using logic gates (AND / OR / NOT)
• comparisons such as ‘is this value greater than that value?’
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– Systems Architecture
Registers
A register is a type of temporary memory located inside the CPU.
It is faster to shift data to and from registers rather than RAM so it
speeds up processing time.
There are many registers inside the CPU
These are a few:
• The accumulator (A or ACC)
• The program counter (PC)
• The memory address register (MAR)
• The instruction register (IR)
• The memory data register (MDR) or memory buffer register (MBR)
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– Systems Architecture
Buses
• A bus is a set of wires or tracks laid down on a printed circuit board.
• Their role is to carry data around the system, connecting the control unit
with other components of the CPU and devices in the computer system.
• The data bus carries data around the system
• The address bus carries information on the location of the data
• The control bus handles commands to control devices e.g. hard disk,
monitor etc
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– Systems Architecture
Fetch –Decode - Execute
The way the CPU is designed and executes the program instructions is
known as ‘von Neumann architechure’.
John von Neumann’s design was for a ‘stored program’ computer where
both the program and the data are stored in memory.
Previously to this computers had to be rebuilt for each new program.
The method designed to execute the programs is known as the:
fetch-decode-execute cycle
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– Systems Architecture
Fetch
In the fetch part of the cycle, instructions and data are
moved from the RAM to the CPU.
Random Access Memory
The program instructions and data
to be used are stored in RAM
Central Processing Unit
The CPU sends a signal to the RAM
requesting the next instruction or
the data to be used.
The instruction or data are sent to
the CPU
Address bus
Data bus
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– Systems Architecture
Central Processing Unit (CPU)
Decode and execute
The decode part of the cycle had the control unit interpret the
instructions and decide what action to perform. During the execute
phase, the instructions are then carried out.
Control Unit (CU)
The control unit decodes
the instructions – decides
what it means and carries
it out.
If a calculation needs to
be performed then it
instructs the ALU
Arithmetric and Logic
Unit (ALU)
If a calculation needs
to be carried out, it is
performed by the
ALU
Instructions
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– Systems Architecture
CPU Recap – fetch-decode-execute
Fetch - instructions and data are moved from the RAM to the CPU.
Decode - the control unit interpret the instructions and decide what
action to perform.
Execute - the instructions are then carried out.
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– Systems Architecture
Multi-core processors
• A multi-core processor has more that one CPU
• Each core has its own ALU, Control Unit and Registers.
• The following diagram illustrates the structure of a dual-core processor
• Having extra cores allows additional tasks to be carried out
simultaneously, thus speeding up the processing time.
• This is called ‘multi-tasking’
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– Systems Architecture
Multi-core processors
Advantages
• The cores can work together on the same program, known as parallel
processing
• The cores can work on different programs at the same time, known as
multitasking
However…
• This doesn’t always double performance as some programs are sequential and
cannot easily be split into two parts. Requiring one task to finish before the
next can begin
Number of cores
Common name
1
2
4
5
8
10
Single-core
Dual-core
Quad-core
Penta-core
Octa(o)-core
Deca-core
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– Systems Architecture
1. The three main factors which affect the performance of a CPU are:
a)
b)
c)
2. During each tick of the clock, how many instructions can be processed?
1 100 1000 1 million
3. How many instructions can a 3 GHz CPU process per second?
4. The higher the clock frequency, the faster the CPU can run
TRUE FALSE
5. There is a limit to the speed that a CPU clock can tick because:
6. To keep the temperature of the CPU down, which of the following are used?
A thermometer A motherboard A heat sink
7. Which of the following ARE part of a CPU core:
Register Heat sink Control Unit Hard diskALU External cache
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– Systems Architecture
1. The three main factors which affect the performance of a CPU are:
a) The clock b) The cores c) The cache
2. During each tick of the clock, how many instructions can be processed?
1
3. How many instructions can a 3 GHz CPU process per second?
3 billion instructions per second
4. The higher the clock frequency, the faster the CPU can run: TRUE
5. There is a limit to the speed that a CPU clock can tick because:
The faster the clock ticks, the more heat is generated. This can damage the CPU
6. To keep the temperature of the CPU down, which of the following are used?
A heat sink
7. Circle which of the following ARE part of a CPU core:
Register Control Unit ALU
9. The cache acts as a temporary buffer between the CPU and RAM
10. The cache stores instructions and data that are frequently been used, have recently been used or
are about to be used.
11. Because instructions and data can be used directly from the cache, it speeds up processing
12. The CPU will always have its own internal cache: TRUE
13. Cache memory is FASTER to access than RAM
14. Cache memory is MORE expensive than RAM
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