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Computer Systems. Nat 4/5 Computing Science Computer Structure: Lesson 5: Processor Structure. Lesson Aims. By the end of this lesson: Pupils at will be able to: Label a computer system in terms of a 5 block diagram Describe the phrase ‘word length’ Describe the purpose of a processor
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Computer Systems Nat 4/5 Computing Science Computer Structure: Lesson 5: Processor Structure
Lesson Aims • By the end of this lesson: • Pupils at will be able to: • Label a computer system in terms of a 5 block diagram • Describe the phrase ‘word length’ • Describe the purpose of a processor • List and describe the parts of a processor: • Control Unit, ALU, registers • Describe what a bus is and does
Nat 4/5 A Basic Computer System • This is known as the 5 block diagram. Backing Storage Processor Input Devices Output Devices Memory
Nat 4/5 The 5 Block Diagram • Input Devices • These are devices that enter data INTOthe computer. i.e. Keyboard and mouse • Output Devices • These are devices that generate output FROMthe computer i.e. printer. • Memory • There are two types of memory. RAM and ROM (more on this later) • Backing Storage • This is required to store permanent copies of our files.
RAM – Random Access Memory • Stores instructions and data that the computer is currently using • Contents are lost when the computer is switched off • User’s data stored in RAM
Read Only Memory • Stores programs and data permanently • Programmed when it’s manufactured • Stores the Operating System • Contents are not lost when the computer is switched off
Nat 4/5 TheProcessor • The processor is the ‘brain’ of the computer. • It is the piece of equipment that actually performs the instructions required. • It can be shown in the following diagram: Processor Control Unit Arithmetic and Logic Unit (ALU) Registers
ProcessorParts Nat 5 Control Unit This controls the order of execution and the timing of the instructions in each program that is running in the CPU Arithmetic and Logic Unit (ALU) This performs the calculations for the processor. It also carries out the Logical decisions like AND, OR, > , <= Registers These are temporary stores of information. Each register can store afew bytes of information like an address or a value
Nat 5 32 bit and 64 bit computing? • You often hear a processor being described as 32 bit or 64 bit. • This is usually referring to the ‘word length’ of the computer • This is the amount of data that can be transferred in a single clock cycle within the computer system • i.e. amount of data that can be moved between the memory and processor at a time
What does a bus do? A bus is a collection of wires which can carry data Nat 5 Processor Main Memory Control Unit Data Bus RAM Address Bus ALU ROM Registers
Nat 5 Buses • Data Bus • The data bus is used to carry data to and from the CPU and Memory. • It will hold a binary word (16 bits in an old Sony Mega Drive, 64 bits in a PS3) • Address Bus • This carries the address of the memory location that is being accessed • Control Bus • Consists of a number of wires e.g. the clock line which regularly pulses with electricity and controls the speed of the processor
Summary The CPU (Central Processing Unit) is the brain of the computer The CPU has 3 main parts • Control Unit • Controls the timing and order of execution of instructions • Arithmetic and Logic Unit (ALU) • Performs the arithmetical and logical functions • Registers • Temporary stores of information Word length is the amount of data that can be transferred in a single clock cycle within the computer system Nat 5 Mnemonic – CAR
