The processor has the following functions: Fetches the next instruction; Decodes the instruction

1. The processor has the following functions: • Fetches the next instruction; • Decodes the instruction • Executes the instruction • Referred to as the FETCH-DECODE-EXECUTE CYCLE • Is the central part of a computer • Sometimes called – Central Processing Unit • Consists of: • Special registers • Arithmetic Logic Unit (ALU) • Control Unit (CU) • Usually also includes: • Main memory • Immediate Access Store (IAS) • Control Unit manages the execution of instructions • It fetches the instruction • Decodes it and synchronises its execution • It then sends control signals to other parts of the processor in order that the instructions are carried out

2. Program counter (PC) • determines sequence in which programs instructions are executed • Memory address register (MAR) • Holds the address of the data (or instruction) currently being accessed • Memory data register (MDR) • The memory is searched to find the address that is being help in the MAR • Current instruction register CIR • The instruction that is now in the MDR is copied into the CIR • It can now be split into parts • One part is sent to computer to be decoded so that the processor knows what sort of instruction it is – and so it can send signals to relevant parts of the processor to carry out the instructions • Another part is an address that tells the processor whereabouts in memory the data is that is to be used • If the instruction is ADD 20 • It will be split up • The control unit works out how to do ADD • And the 20 is where the processor will find the data that has to be added • The address part (20) is sent back to the MAR • The memory is then searched & whatever is in the address 20 is copied into the MDR • The value in the MDR can then be used according to the instruction in the CIR • If the instruction is to do some arithmetic or logical comparison the data is sent to the Accumulator that will carry out the task • The Accumulator • The Accumulator (ACC) is used to accumulate results

3. Other processor architectures • Co-processor • Not all data are stored in the same number of bytes • Some require significantly more bytes than others • A processor that is capable of processing large representations in one operation is called a maths co-processor • Is a second processor in your computer that does nothing but number crunching for the system • Addition, subtraction, multiplication, and division of simple numbers is not the coprocessors job. • It does all the calculations involving floating point (decimal) numbers, such as scientific calculations and algebraic functions. • The CPU is perfectly capable of doing these functions and calculations. • that used to be part of its job. • Most of the older computers were sold without coprocessors. • So the CPU had to process all the computer's hardware and software functions, handle all interrupt requests, and direct all information and data, as well as performing all floating point calculations. • This required a lot of the processor's time. • By having a second processor, or 'coprocessor', to take over the number crunching, it can free up a lot of the CPU's precious time • This would allow the CPU to focus all of its resources on the other functions it has to perform, increasing the overall speed and performance of the entire system • The absence of a math coprocessor in early computer systems was a matter of keeping production costs down • The advantage was recognized right from the beginning, and most of motherboards had an empty slot for the aftermarket addition of a coprocessor. • Array processor • An extension to the CPU’s arithmetic unit, • Allows any instruction to operate simultaneously on multiple data locations • The same calculation on different data is very fast • used in time dependent operations which require large amounts of processor time • Weather forecasting for example • Common uses include analysis of fluid dynamics and rotation of 3D objects as well as data retrieval, in which elements in a database are scanned simultaneously

4. Parallel processors • A number of processors working together in order to speed up complex processing tasks • However, special programming has to be done to control this process • How it works: • More than one processor • controlled by a complex operating system • working together • to perform a single job • which is split into tasks • each task may be performed by any processor • Advantages • increased speed/multiple instructions processed at once • complex tasks performed efficiently • Disadvantages • not suitable for some programs • programs written specially/may need to be rewritten • Categories Processors • These programs, however simple, will eventually be translated into machine code instructions • Each will contain a specific operating code • Each type of processor uses a specific set of operations which are specified during manufacture • One way to categories processors is to indicate the number of different instructions recognised

5. CISC - Complex Instruction Set Computer • Means a computer that can recognise and use many machine code instructions • CISC technology combined the different instructions into one single CPU, and each instruction had the ability to perform several different tasks based on mini-programs or microcode integrated into the processor • An increased number of instructions (200 to 300) meant a much more complex processor, requiring millions of transistors. • Instructions were different lengths, using 8, 16, or 32 bits for storage. • This resulted in a great deal of the processor's time being spent calculating where each instruction began and ended • One of the biggest drawbacks wasn't realized until later. • Thousands of Application Software programs had been written for the processor, any new chips developed had to be backwards compatible • Which limited the ability for engineers to take advantage of new discoveries and advancements being made in processor technology • RISC - Reduced Instruction Set Computer • This reduction generally leads to faster processing • However does mean some instructions require a combination of simpler instructions • Led to a more stable, cooler operating CPU. • Each instruction is a fixed size (32 bits). • This means that the processor doesn't have to use up any of its valuable time figuring out where each instruction begins/ends

6. DISCLAIMER: NONE OF THE INFORMATION IN THIS POWERPOINT PRESENTATION WAS COPIED FROM MR KEVIN JEFFERIES STUDENT RESOURCES ON THE VLE. ANYONE WHO THINKS SO, INCLUDING YOU MR KEVIN JEFFERIES, CAN TAKE IT UP WITH ME AFTER LESSON. RESPECT GEORGE MASTER PROGRAMMER, INVENTOR, GENIUS, GOD LIKE HUMAN BEING, AND AWESOME COMPUTING STUDENT. THIS CLAIM WAS CONFIRMED IN A POLL OF AWESOME BRITS IN THE INDEPENDANT BROAD SHEET NEWSPAPER. IF YOU DO WISH TO TAKE ME ON AFTER THE LESSON I MUST WARN YOU I ONCE FOUGHT A CANADIAN BROWN BEAR WEIGHING IN AT 300 POUNDS WITH A BROKEN RIGHT HAND. I ALSO BEAT ALDREY HARRISON IN AN ARM WRESTLING COMPETITION WITH MY LEFT HAND AND IM NOT EVEN THAT GOOD WITH MY LEFT HAND! ARGGGGGGGGGGGHHHHHHHHHHHHHHHHHH! I’M BORED!