gcse function and characteristics of ocr the cpu
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GCSE OCR Computer Science J276
Function and characteristics of the CPU
Unit 1 System architecture, memory and storage
• Describe common CPU components and their function: ALU Arithmetic Logic Unit), CU (Control Unit), cache
• Describe how common characteristics of CPUs affect their performance: clock speed, cache size, number of cores
• Explain the purpose and give examples of embedded systems
Objectives
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
A brief recap • What are the two major components of the CPU?
• What is their purpose?
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Arithmetic Logic Unit (ALU) Performs two sorts of operations on data:
• Arithmetic operations • addition, subtraction, multiplication, division
• Logical operations • comparing one data item to another: is it smaller than, greater
than or equal to?
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
The Control Unit “The control unit co-ordinates and controls all the operations carried out by the computer.”
• Controls and monitors hardware attached to the system
• Controls input and output of data
• Controls the flow of data within the CPU
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
What affects CPU performance? • The following are three of the most common factors
which can affect a CPU’s performance • Clock speed
• Processor cores
• Type and size of memory
• Which have you heard of?
• Can you explain them?
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Factors affecting CPU performance
Clock speed Cache size
Number of cores
Cycles per second measured in hertz
The number of duplicate processors linked together on a single chip
Superfast working memory
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Clock speed • Everything in a computer happens on the pulse of
the internal clock
• Therefore, the faster the clock speed, the faster the instructions are processed
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Processor Speed • One cycle per second = 1 Hertz (Hz) = 1 instruction
carried out each second
• 1 Kilohertz (KHz) = 1000 cycles per second
• 1 Megahertz (MHz) = 1,000,000 cycles per second
• 1 Gigahertz (GHz) = 1,000,000,000 cycles per second (Approximately 1 billion!)
• How fast is your computer’s processor?
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Multi-core processors • A dual-core processor has two processors in the
same integrated circuit, linked together
• A dual-core processor has twice the power but does not always perform twice as fast, because the software may not be able to take full advantage of both processors
• A quad-core processor has four linked processors
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Effect on speed • A quad-core processor working on many different
tasks simultaneously, under ideal conditions can be up to 4 times faster than a single-core processor
• If the computer is running a single program, it is not necessarily any faster, since instructions have to be carried out in sequence
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Cache memory • Cache is a small amount of very
fast, expensive memory in the CPU
• It can be accessed faster than regular main memory (RAM)
• Why is this useful for frequently used data?
CPU
Cache
Main Memory
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Effect on speed of cache • RAM is relatively slow memory and it is further away
from the processor than cache
• It takes longer to retrieve an instruction or data from RAM than from cache
• Program instructions and data that are fetched are stored in cache in case they are needed again soon
• If you have a “while” loop in a program, for example, having all the instructions in the loop in cache speeds up execution
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Levels of cache memory • There are different ‘levels’ of cache:
• Level 1 cache is extremely fast but small (between 2-64KB), located on the CPU
• Level 2 cache is fairly close to the processor, fairly fast and medium-sized (256KB-2MB)
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Levels of cache memory
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
The benefits of cache • The data used most often by the CPU is held in Level
1 cache so is instantly available
• In most systems, other data needed by the CPU is accessed from the Level 2 cache 95% of the time
• This greatly reduces the time that the CPU has to wait for data from main memory
• The size of the Level 2 cache, and whether it is actually on board (on the CPU) is a major factor in determining the performance of the CPU
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Which is (theoretically) faster? 1. A dual core processor running at 2.7GHz with 4Mb of
shared cache memory
2. A quad core processor running at 1.5GHz with 8Mb of shared cache memory
3. A single core processor running at 3.2GHz with 2Mb of cache memory
4. A dual core processor running at 3.2GHz with 4Mb of shared cache memory
Calculate the maximum number of cycles per second in each case and rank them in order of performance
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Worksheet 2 • Complete Task 1: The Central Processing Unit
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Embedded systems • Do these devices have inputs, processes and
outputs? • Could they be classed as computers?
• Why? Why not?
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Embedded computers • An embedded computer is a single microprocessor
that includes RAM, ROM and a CPU • An embedded computer is frequently used to control a device
using simple controls
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Embedded systems • Without embedded systems, a digital device would
not be able to perform specific functions • For example, a dishwasher wouldn’t know how to heat the
water, or a satnav wouldn’t know how to communicate with a satellite
• What embedded functions do cars use?
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Worksheet • Complete Task 2
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Plenary 1. What is the main purpose of the CPU?
2. How does the CPU operate?
3. Name three common factors which affect how fast a CPU can perform
4. What is an embedded system?
5. Name three examples of an embedded system
Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage
Plenary – Answers 1. Fetch, Decode and Execute data
2. Fetches instruction/data from RAM, decodes the instruction/data and makes sense of it, executes the instruction/data. This is then repeated
3. Clock speed, number of cores, cache size
4. A single chip that contains all of the elements that are essential for any computer
5. SatNav, Microwave, Car, Dishwasher, Burglar alarm, Washing machine…
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Function and characteristics of the CPU Unit 1 Systems architecture, memory and storage