CPU Describe the purpose of the CPU Understand how ROM, RAM, I/O, storage link to CPU Explain performance of CPU – looking at clock speed, cores & cache

The CPU– Theory  The CPU (Central Processing Unit) is hardware that executes programs and manages the rest of the computer system. It sits underneath the heat sink on the motherboard and is made up of millions of electrical switches called transistors. All data is stored within a computer as electronic signals in micro-circuits. There are only 2 types of signal –on or off. A micro-circuit can either carry an electrical signal or not. This will lead to our discussion of binary later in the course. The CPU is often known as the “brains” of the computer and its purpose is to process data. It does this by performing functions such as calculating, decision making and moving data around. Our computers would not work if not for the CPU, similar to us not functioning without our brain! Think of all the tasks our computer does. Write a list of 10 jobs. Eg. Perform a function on a spreadsheet…

The CPU …the CPU will deal with all the data processing, without it none of your tasks will be performed. The first CPU chip was invented in 1971 – a 4 bit processor designed for a calculator! This is where our story starts… Processor speed has doubled over time while a second processor has resulted in the phrase dual-core which is a double processor – doubling the speed. It doesn’t stop there, quad-core, hexa-core and octa-core offer the next steps to power our machines even faster. Software running on our systems have to be designed to take full advantage of all these new progressions. Current mobile devices will carry mobile processors; small versions without fans to keep it cool.

How it all fits together You input information and commands using the mouse and keyboard. You see/hear the results on the output devices- screen and speakers The CPU ("processor") is the working brain of the computer, that does all the processing and computation The memory ("RAM") is where the CPU keeps information it is working with (the information in the RAM is lost when the computer is switched off) Storage (e.g. hard-disks, USB data sticks) is where the computer keeps information for longer periods (not lost when the computer is off)

Elements of the CPU The CPU consists of 3 major components: The Arithmetic and Logic Unit (ALU) The Memory Unit The Control Unit (CU) The ALU – carries out mathematical tasks rapidly, performs calculations and logic operations in binary form 1/0 on data from the memory unit. The ALU transforms the digital data and outputs the resulting value. The Memory Unit consists of a small number of memory registers which will store items of data and send them to the ALU for processing. The result of the processing will be copied back to the memory unit for storage. The CU – is in charge of processing. It interprets the software instruction and sends the right data and operation to the ALU. It accepts the result of the processing from the ALU and sends it back to the memory unit. The CU will keep track of the sequence of instructions and the location of each item of data and software instruction in the memory unit.

What does a computer do? It runs a computer program What is a program? Program : the sequence of instructions stored in ‘memory’ required to solve a specified problem Computer architecture:

An Analogy

An Analogy

Fetch-Execute Cycle Analogy Fetch : read instruction from cook book. Decode : understand instruction and get ingredients from store Execute : crack egg into bowl.

Fetch-Execute Cycle The CPU will typically perform the following execution cycle: The CU fetches a single instruction and data from the main memory The instruction is decoded. The ALU executes the instruction The ALU sends the result of the processing back to the control unit – this is stored in the memory unit.

A Ride on a Bus Just how does the CPU interact with the rest of the system? A bus or a cable (a collection of fine wires) The System Bus is a major component of a computer: Data Bus: Carries the data that needs processing Address Bus: Determines where data should be sent Control Bus: Determines data processing

RAM/ROM & the CPU ROM & RAM are memory areas that are closely linked to the CPU. RAM is the type of memory used in the computer’s main memory. RAM is the active memory of the computer. The contents of all open software applications and data files are held in RAM. So when a program is running it has to be loaded from the hard disk into the main memory so the processor can access the instructions. RAM acts as temporary storage for programs and data just while it is running. This makes it volatile. Once the program has finished and closed it is no longer main memory. ROM is Read Only Memory – you can not write over the contents once it has been created. This makes it non-volatile. More on ROM & RAM later in the course…

Clock Speed The power and speed of a computer is limited by the speed with which the computer can carry out the fetch-execute cycle. Computers can only process one instruction at a time. If you are running many programmes eg. Surfing the net, working on an essay, listening to music and sending an e-mail all at the same time (multi-tasking) it may seem that the computer is processing all these tasks simultaneously. In reality it is handling one instruction at a time but it does it rapidly! The amount of time the CPU has to process each instruction is controlled by a quartz clock, with every tick the CPU is able to process one piece of data or execute one instruction. The CPU clock speed is measured in cycles per second. 1 cycle peer second is known as 1 Hertz. A computer running at 1GHz can carry out a thousand million instructions per second. So the speed of the clock determines the basic performance of the CPU – the faster it goes, the more powerful the computer. If the CPU has more than one core, it can execute more than one instruction.

Cache Memory Cache memory is memory that can be accessed rapidly by the processor. It holds a copy of the data that is stored elsewhere. If the processor has to access main memory less often it can work faster so the CPU performs better. The data that the computer needs right away is taken from storage before processing begins and kept in cache memory while it is in use. There are several types of cache: The memory register is very small cache, it holds data for immediate use. L1 cache is small, fast and expensive L2 cache is larger but slower In programming a cache library can be used for storing database queries for later use.

Key Terms CPU The central processing unit of a computer. Hardware that executes programs and manages the system ALU The arithmetic and logic unit. Part of the CPU where data transformation occurs. It operates electronically. Fetch-Execute Cycle A single operation of the CPU: a stored instruction is taken from memory, carried out and the resulting value stored to memory. Dual-Core Processor A CPU with 2 processing components to speed up tasks Cache Memory Acts as a buffer between main memory and the CPU – “fast memory” ROM Read Only Memory – Not Volatile RAM Random Access Memory - Volatile

Prep – Read over all slides Fill in the blanks with the given words NAME: ______________