The CPU, RISC and CISC Component 1

Learning Intentions Learning Intention: To identify what the CPU is, does, and how it works! Describe the characteristics of CPU architecture, including Von Neumann architectures. Identify and explain the role of the components of the CPU in the fetch-decode-execute cycle. Explain how performance is affected by the cache size, clock speed and number of cores. Explain the difference between RISC and CISC types of processors

Starter: pre-reading Find today’s lesson folder and open the pre-reading document. Try and answer the following questions in your books about CPU’s: What does CPU stand for? What does it do? What are the main parts of a CPU? What do they do? Where does the CPU store data? What are the 3 and what do they do?

Central Processing Unit (CPU) The Central Processing Unit or CPU is arguably the most important component of a computer What does it do? If it was one organ in the human body what would it be?

Central Processing Unit (CPU) You can think of the CPU is being like the brain in a human It is responsible for all of a computers processing

The purpose of the CPU The CPU is split into many parts internally Two of its major components are: The Control Unit The ALU Control Unit Arithmetic Logic Unit (ALU) Main Memory (RAM) Central Components of a Computer CPU

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

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?

Registers Where does the CPU store things whilst it is executing commands or performing calculations? Registers! A register is a storage location found on the CPU where data or control information is temporarily stored. Registers are usually much faster to access than internal memory, since they have to be accessed so often.

Registers Program Counter (PC) – a counter that keeps track of the memory address of which instruction is to be executed next. Memory Address Register (MAR) – the address in main memory that is currently being read or written. Current Instruction register (CIR) – a temporary holding area for the instruction that has just been fetched from memory.

How does the CPU transfer data?

Buses Buses allow data to be transferred to different parts of the computer. There are three main buses used by the CPU. Address bus. When data is saved or loaded from memory, the address at which it is to be stored or loaded from must be sent. The storage address of data always travels along an address bus. Data bus. Data will then need to be moved between several parts of a computer. The path along which data travels is called a data bus. Control bus. The controller uses the control bus to send control signals to different parts of the computer.

Group Activity: Von Neumann In your groups find out what the Von Neumann architecture is. You should consider: What it does The different stages How they work together!

The Fetch - Decode - Execute cycle

Perform an arithmetic or logical operation The Fetch - Decode - Execute cycle Fetch Step Execute Step Main Memory Load data from memory Store data in memory Perform an arithmetic or logical operation Decode Step CPU Program Counter

Fetch – Decode – Execute The CPU operates by repeating three operations: FETCH – causes the next instruction and any data involved to be fetched from main memory DECODE – decodes the instruction to make sure it can be carried out EXECUTE – carries out the instruction Repeat…

What affects CPU performance? The following are three of the most common factors which can affect a CPU’s performance Clock Speed Number of Cores Cache Size Which have you heard of? Can you explain them?

Factors affecting CPU performance Clock speed Cache size Cycles per second measured in hertz Superfast working memory Number of cores The number of duplicate CPUs on a single chip

Graded Exercises You must complete the grade 4 exercises before you move on. You can use the pre-reading, PowerPoint, Internet, or the Help! Folder to help you complete the grade 4 exercises. When you have completed grade 4 you can move on to the grade 5-7 exam questions. (You will need to print these).

RISC and CISC There are two main types of processor, namely Reduced Instruction Set Computer (RISC) and Complex Instruction Set Computer (CISC). RISC processors can process a limited number of relatively simple instructions. To carry out more complex commands the problem is broken down into a longer list of simpler instructions. The advantage of this is that a RISC processor is able to process these simpler instructions quickly. Processing simpler instructions also requires less circuitry to decode and execute these instructions, which in turn means less power consumption and therefore less heat being generated.   CISC processors can process a large number of complex instructions. This allows the processor to understand and carry out complex tasks with only a few instructions. The advantage of this is that a CISC processor is able to process complex instructions, without having to break them down into many simpler instructions. Processing complex instructions however requires more circuitry to decode and execute these instructions, which in turn means more power consumption and therefore more heat being generated.

Plenary: Crib Sheets Every lesson you will create an exam ‘crib’ sheet that you will use to revise for your SATs and your exam. A ‘crib’ sheet is short form notes that help you remember the key facts. For example: The CPU is the Central Processing Unit The Program Counter keeps track of the next instruction to be executed The easiest way to create a crib sheet is to look at the exam board textbook and write short hand notes!

Crib Sheet – What I must remember about the ___ Record the key facts that you need to remember about the CPU. Think about what you have learnt today, what questions you have been asked, definitions of words, or anything else you think is important!

Homework – pre-reading and question sheets Every week your homework will be to: answer question sheets for the topic covered in lesson read ahead for next week – making notes that will help you create your crib sheets This week you will: make notes on: page 10 of the pre-reading text book. Question sheets: 6 – The CPU