[Music] hello and welcome to this GCSE computer science video with me Mr Goff for Mr go.com this video will'll focus on the architecture of the CPU the CPU is the central processing unit the role of the CPU is to process instructions by running the fetch to code execution cycle the CPU is often thought of as being the brain of the computer the CPU is made up of a number of special components as seen below these are the ones that you need to be aware of for the exam the arithmetic logic unit this handles all mathematical operations and comparisons it also handles logical operators such as and or and not the control unit this decodes instructions and controls and coordinates the movement of data around the CPU based on the tick of the clock the cache this is very fast but small memory locations for storing recently and frequently used instructions and registers these are super fast storage locations located on the CPU for storing instructions and data as they are processed as well as the general purpose registers that store instructions and data as the program executes the CPU also contains some special registers that have specific purposes the four you need to know about for the exam are shown below the program counter stores the address of the next instruction to be fetched and executed the memory address register temporarily holds the address of the next instruction or piece of data to be fetched so that the computer knows where to fetch it from the memory data register temporarily holds the actual instruction or piece of data that has just been fetched until it's needed the accumulator holds values that are directly loaded into it as well as the results of calculations made in the arithmetic logic unit at the fet stage of the fetch toode execute cycle the program counter holds the address of the next instruction this address is transferred to the memory address register at this point the program counter is incremented so it points to the next instruction to be fetched and executed next the instruction at the address specified by the memory address register is returned from RAM and placed in the memory data register at the decode stage the control unit decodes the instruction by comparing the binary instruction it received with its instruction set to work out what needs to be done if the instruction requires some data to be fetched such as the instruction add 105 the address of the data that needs to be fetched will be passed to the memory address register if there is extra data required when it is fetched from the address in memory address register it will be returned to the memory data register at the execute stage the instruction is carried out if we return to our example of the instruction add 105 this would add the value of the data stored in register 105 to what is already in the accumulator it is important for the exam that you are able to specify whether a certain register holds data or an address so the table belong summarizes this information the program counter holds an address the memory address register also holds an address the memory data register holds either an instruction or data the accumulator holds data that brings us to the end of this video on the architecture of the CPU join me in the next video when I'll be looking at the factors that affect CPU performance use the resources at mr.com to help you revise computer science and until next time it's bye for now [Music]