1.1 Systems Architecture

What is a computer?

Electronic device that:

• Takes input

• Processes data

• Delivers output

What is the purpose of the CPU?

Fetch, decode, and execute instructions

What happens in the fetch stage?

• Next instruction fetched from main memory

• Stored using registers

What happens in the decode stage?

Instructions are inspected to find out what needs to be done

What happens in the execute stage?

• Going back to main memory — fetching data

• ALU performing calculation

• Storing information in main memory

Describe what happens during the fetch-execute cycle

• Instructions fetched from main memory

• Instructions are decoded

• Instructions are executed

  • ALU performs arithmetic calculations

What components does the CPU consist of?

• ALU — arithmetic logic unit

• CU — control unit

• Cache

• Registers

What is the function of the ALU?

Performs:

• mathematical calculations

• logical operations

• binary shift operations

What is the function of the CU?

• Sends signals to coordinate processor

• Decodes instructions

What is the function of the cache?

Provides fast access to frequently used instructions and data

What are registers?

• Tiny, very fast pieces of onboard memory inside CPU

• Have specific purposes

What does the Von Neumann architecture consist of?

• CU — control unit

• ALU — arithmetic logic unit

• RAM — random access memory

• Inputs and outputs

What concept is the Von Neumann architecture based on?

Stored program concept

Von Neumann Architecture:

Both ____________ _______ and ____________ _______ are stored in the same memory in ________ form.

• instruction data

• program data

• binary

What registers are in a Von Neumann CPU?

• PC — program counter

• MAR — memory address register

• MDR — memory data register

• ACC — accumulator

What is the function of the PC?

• Holds address of next instruction to be executed in memory

• Increments in each FDE cycle

What is the function of the MAR (memory address register)?

Holds memory address where data is to be fetched from or written to

What is the function of the MDR (memory data register)?

Holds data fetched from memory

What is the function of the ACC (accumulator)?

Holds results of calculations performed by ALU

Why is the fetch-execute operation of a CPU described as a cycle?

Once one instruction has been fetched and executed the CPU can fetch and execute the next one

Give three characteristics of a CPU that can affect its performance.

• Clock speed

• Cache size

• No. of cores

What is clock speed?

• Number of cycles clock sends per second — measured in Hz

• 1GHz = 1 billion cycles per second

What effect does higher clock speed have on CPU performance?

• More FDE cycles per second

• More instructions processed in given time

• Improves performance

What effect does cache size have on CPU performance?

• Larger cache = more frequently used data and instructions stored

• Reduces no. of times CPU accesses main memory

What is cache?

Memory that provides fast access to frequently used instructions and data

Explain one reason why the cache size affects the performance of the CPU.

• Data transferred faster

• Makes CPU more efficient

What is a core?

Processing unit inside CPU

What effect does the number of cores have on CPU performance?

Multiple instructions can be processed simultaneously — improves performance

Why won’t doubling cores always double performance?

• Cores must communicate

• Some programs aren’t designed to use multiple cores

• The specification of two CPUs is shown in Fig. 1.

Computer 1	Computer 2
Clock Speed: 1 GHz	Clock Speed: 1.4 GHz
Cache size: 2 MB	Cache size: 2 MB
Number of Cores: 4	Number of Cores: 2

• When running a 3D flight simulator, Computer 1 is likely to run faster than Computer 2.

Using the information in Fig. 1, identify one reason for this. [1]

More cores

• The specification of two CPUs is shown in Fig. 1.

Computer 1	Computer 2
Clock Speed: 1 GHz	Clock Speed: 1.4 GHz
Cache size: 2 MB	Cache size: 2 MB
Number of Cores: 4	Number of Cores: 2

• When running a 3D flight simulator, Computer 1 is likely to run faster than Computer 2.

Identify two other parts of a computer that are not in Fig. 1, which could improve the performance of the computers. [2]

• RAM

• SSD

What is an embedded system?

Computer built with dedicated function inside a larger device

What are the typical properties of an ambedded system?

• Low power consumption

• Small size

• Rugged operating ranges

• Low cost per unit

What are examples of embedded systems?

• Traffic lights

• Domestic appliances

• Factory equipment

• Engine management systems

• Hospital equipment

• A car has a ‘Follow Me’ system that uses a cruise control feature to allow the car to follow the car in front of it.

• It will keep the same speed and distance without the driver’s intervention.

• The cruise control system is an example of an embedded system.

Explain the reasons why the ‘Follow Me’ system is an example of an embedded system. [3]

• Has specific purpose

• Built inside larger device

• Has a microprocessor

• A car comes with many embedded systems, for example parking sensors.

Identify one other embedded system that could be found in a car and explain why this is an embedded system. [3]

• Auto lights

  • Limited functions

  • Dedicated microprocessor

• The following paragraph describes embedded systems.

Complete the paragraph by selecting terms from the list and writing them in the correct places. Not all terms are used. [4]

Embedded systems have limited ......................................................…

They are often built into a ........................................................ machine.

Two examples of embedded systems are a ........................................................ and automated ........................................................ in a car.

• functions

• larger

• washing machine

• lights