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The Fetch / Execute Cycle

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Ryan Doray

on 9 February 2012

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Transcript of The Fetch / Execute Cycle

Fetch Decode EXECUTE The fetch execute cycle is the time period of which the computer reads and processes the instructions from the memory, and executes them. This process is a continuous cycle which is used until the computer is turned off or there are no more instructions to process.

Fetch / Execute Cylce What it is CONTROL UNIT: General Operations The control unit controls the flow of data through the processor, and coordinates the activities of the other units within it. In a way, it is the "brain within the brain", as it controls what happens inside the processor, which in turn controls the rest of the computer. CONTROL UNIT: Functions of the Control Unit The control unit performs the tasks of fetching, decoding, managing execution and then storing results. ALU: What it is In computing, an arithmetic logic unit is a digital circuit that performs arithmetic and logical operations. The ALU is a fundamental building block of the central processing unit of a computer, and even the simplest microprocessors contain one for purposes such as maintaining timers. ALU: Purpose of the ALU Most of a processor's operations are performed by one or more ALUs. An ALU loads data from input registers, an external Control Unit then tells the ALU what operation to perform on that data, and then the ALU stores its result into an output register. INSTRUCTION REGISTER: What it is and what it does In computing, an instruction register is the part of a CPU's control unit that stores the instruction currently being executed or decoded. In simple processors, each instruction to be executed is loaded into the instruction register which holds it while it is decoded, prepared and executed. PROCESSOR REGISTER: What it is and what it does In a processor register is a small amount of storage available as part of a CPU or other digital processor. Almost all computers load data from a larger memory into registers where it is used for arithmetic, manipulated, or tested, by some machine instruction. CACHE: What it is The cache is a smaller, faster memory which stores copies of the data from the most frequently used main memory locations. As long as most memory accesses are cached memory locations, the average latency of memory accesses will be closer to the cache latency than to the latency of main memory. CACHE: What it does Most CPUs have at least three independent caches: an instruction cache to speed up executable instruction fetch, a data cache to speed up data fetch and store. CACHE CONTROLLER: What it is The cache controlller detects cache misses and controls sending and receiving the cells. This device also controls the perhaps interface, in the case of contention for transmission to the fabric the cache section always wins. ALU: What it does The Arithmetic Logic Unit performs all the mathematical calculations of the CPU. The ALU can add, subtract, multiply, divide, and perform a host of other calculations on binary numbers.
RAM: What it does This component is created from combining latches with a decoder. The latches create circuitry that can remember while the decoder creates a way for individual memory locations to be selected. RAM: What it is Random access memory (RAM) is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Machine Cycle I-TIME: What it is and what it does E-TIME: What it is and what it does The execution series also can be explained as the time duration or period in which the given command is executed and then the end result is just saved in a register and it might also be known as the E-cycle or the E-time. When ever the central processing unit or the CPU gets the commands from main memory to carry out a particular process, the phase of time it takes to recover the instruction and set off the task is adverted to as the instruction cycle and might also be known as the I-cycle or the I-time.
A machine cycle is composed of the instruction cycle in addition to one or more execution cycles. SYSTEM CLOCK: General Operations The central processing unit has an internal clock that syncs all of the procedures and processes in the cycle and the clock speed aids or assists to decide the speed at which the processes are carried out. Instruction Pipeline: Its Purpose An instruction pipeline is a technique used to increase the number of instructions that can be executed in a unit of time. Pipelining doesn't reduce the time it takes to complete an instruction. Pipelining increases the number of instructions that can be processed at once, thus reducing the delay between completed instructions. Ryan Doray Stage 2 Computer Science Year 11
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