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An overview of the CPU
The CPU (central processing unit), is one of the main pieces of hardware in a
computer. It controls how data flows between components and is the `brain'
of the computer.
It uses a simple cycle of FETCH, EXECUTE and DECODE.
The CPU consists of four main parts:
ALU (Arithmetic Logic Unit)
CU (Control Unit)
IAS (Immediate Access Storage)
Data flows between all these parts through the use of three main buses:
Address Bus
Data Bus
Control Bus…read more

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The ALU (Arithmetic Logic Unit)
The ALU carries out calculations and logical decisions within the CPU.
It carries out mathematical calculations on binary numbers and logical
decisions such as AND/OR/NOT on data.
It executes commands given in to it, or stores it in one of the registers (The
Accumulator) for its later use.
It also holds data ready to be processed.…read more

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The CU (Control Unit)
The CU sends out signals which co-ordinate how the CPU works.
It controls how data is moved between the CPU and the memory, and also
decodes data from the memory and sends it to the ALU.
For this reason, the CU essentially controls the entire FETCH-EXECUTE cycle
and manages how instructions (in the form of programs) are executed.
It also controls how the input and output devices should respond to an
instruction.…read more

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The Registers
The Registers are essentially memory locations found within the CPU. There
are seven main registers, which each hold specific types of data.
Program Counter: Holds the address of the next instruction to be fetched and executed.
Current Instruction Register: Holds the current instruction.
Memory Address Register: Holds the RAM address you want to read/write from.
Memory Data Register: Holds the data read or to be read to RAM.
Accumulator: Holds data being worked on.
Status Register: Holds information about the last operation.
Interrupt Register: Holds details about whether an interrupt has occurred.…read more

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Buses allow data to travel between different components. There are three
Address Bus: Carries the address of memory locations.
Data Bus: Transfers the binary data between the stated memory locations.
Control Bus: Sends signals around the PC to control when things happen.…read more


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