GCSE OCR Computing A451 The CPU 2-1-2 Computing hardware 1

Objectives State the purpose of the CPU Describe the function of the CPU as fetching and executing instructions stored in memory Explain how common characteristics of CPUs such as clock speed, cache size and number of cores affect their performance

What is this?

The CPU

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 main components of a computer MAIN MEMORY AUXILIARY STORAGE CENTRAL PROCESSING UNIT (CPU) INPUT DEVICES OUTPUT

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

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?

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

Registers Little storage locations that hold one instruction. These are there waiting to be processed Once processed the registers are deleted and the process starts again.

Cache Short term volatile memory Speeds up the process of the computer as the cache is in the CPU 3 Mb capacity

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

Processor Speed How fast is your computer’s processor? One cycle per second = 1 Hertz (Hz) = 1 instruction carried out each second 1 Kilohertz (KHz) = 1024 cycles per second 1 Megahertz (MHz) = 1,048,576 cycles per second 1 Gigahertz (GHz) = 1,073,741,824 cycles per second (Approximately 1 billion!) How fast is your computer’s processor?

Cache memory Cache is a small amount of memory in or near the CPU When an instruction is fetched from main memory it is copied into the cache so if it is needed again soon after, it can be fetched from the cache instead which is much quicker than going back to main memory CPU Cache Main Memory

Which is faster? A dual core processor running at 2.7GHz with 4Mb of shared Level 3 Cache A quad core processor running at 1.5GHz with 8Mb of shared Level 3 Cache A single core processor running at 3.2GHz with 2Mb of shared Level 3 Cache A dual core processor running at 3.2GHz with 4Mb of shared Level 3 Cache Calculate the maximum number of cycles per second in each case and rank them in order of performance

Worksheet 1 The Central Processing Unit

Plenary What is the main purpose of the CPU? How does the CPU operate? Name three common factors which affect how fast a CPU can perform