Central processing unit (CPU) The CPU is the brains of the computer, and is also known as the processor (a single chip also known as microprocessor). This electronic component interprets and carries out the basic instructions that operate the computer. Cache as a rule holds data waiting to be processed and instructions waiting to be executed. The main parts of the CPU are: control unit arithmetic logic unit (ALU), and registers – also referred as Cache registers The CPU is connected to a circuit board called the motherboard also known as the system board. Click here to see more information on the CPU Let’s look inside the CPU and see what the different components actually do and how they interact Control unit The control unit directs and co-ordinates most of the operations in the computer. It is a bit similar to a traffic officer controlling traffic! It translates instructions received from a program/application and then begins the appropriate action to carry out the instruction. Specifically the control unit: controls how and when input devices send data stores and retrieves data to and from specific locations in memory decodes and executes instructions sends data to other parts of the CPU during operations sends data to output devices on request Arithmetic Logic Unit (ALU): The ALU is the computer’s calculator. It handles all math operations such as: add subtract multiply divide logical decisions - true or false, and/or, greater then, equal to, or less than Registers Registers are special temporary storage areas on the CPU. They are: used to store items during arithmetic, logic or transfer operations. An item is usually held in the register only long enough for a specific purpose. there are general purpose registers that simply store data, and special purpose registers that are only used for a specific function, such as the accumulator, program counter and instruction register. Use the site below to find out more. http://educate.intel.com/en/TheJourneyInside/ExploreTheCurriculum/EC_Microprocessors/ Did you know that a CPU is made from SAND? 1 The CPU also requires the use of the following The Bus The bus transfers data between the components contained inside your computer at various speeds. The CPU is referred to as the brains of your computer; the bus is referred to as the spine. It transports data to and from your modem, sound card, graphics adapter, hard drive, RAM, CD-ROM and the CPU. The computer bus consists of two parts: 1. the address bus transfers information about where the data should go 2. the data bus transfers actual data The bus transports chunks of data in the form of bits down a bit-path. Therefore the wider the bit path, the more bits can go through each second – like a multi-laned motorway. The higher the capacity of the components such as the processor and graphics adapter etc., the wider the bus bit- path needs to be to transport the data quickly and efficiently. Bit-path standard sizes are 8-bit, 16-bit, 32-bit or 64-bit, but modern CPUs only use 32 and 64-bit. System Clock The processor relies on the system clock to control the timing of all computer operations and is generated by the motherboard. The computer clock speed is measured in gigahertz (GHz). Giga stands for ‘billion’ and hertz is ‘of cycles per second’. Therefore a computer that has a clock speed of 3 GHz does 3 billion clock cycles in one second. The system clock is NOT the computer clock that you see on your screen. Memory Consists of electronic components that store instructions, data and results. The basic unit of memory is a bit, that is a single 1 or 0. The Instruction Cycle A computer operates by copying bytes from the memory or an input device onto the CPU, performing some calculations on those bytes, and then copying the result of the calculations to the memory or an output device. This process continues in a cycle For this cycle of data processing to be useful, the computer needs to have instructions that tell it what to read and write, and which calculations to perform. These instructions tell the CPU what memory location to read from (fetching data from memory) or write to (storing data to 2 memory), and which input or output devices to access. We call the calculate part of the cycle – PROCESS. The instructions that a computer runs are simply numbers like any other data, and they are stored in the computer’s memory. The CPU always keeps an internal record of which memory location (address) contains the next instruction that it will execute. When it completes one instruction, it reads the next instruction from memory, and updates its record to point to the instruction after that. After it has updated its record, it can process the instruction that it has just read from memory. So a computer program is just a series of bytes that contain instructions for the CPU. When the computer runs the program, it moves sequentially through the set of instruction bytes, loading each instruction onto the CPU, performing that instruction, and then going back to fetch the next instruction onto the CPU. 3 4 .