Structure and role of the processor

Structure & Role of the processor:

Structure & Role of the processor

Who makes Processors?:

Who makes Processors?

Why study hardware?:

Why study hardware? Phyciatrist

From the Specification:

From the Specification Candidates should be able to: describe the function and purpose of the control unit, memory unit and ALU (arithmetic logic unit) as individual parts of a computer; explain the need for, and use of, registers in the functioning of the processor (Program Counter, Memory Address Register, Memory Data Register, Current Instruction Register and Accumulator); explain the need for, and describe the use of, buses to convey information (Data, Address and Control buses);

Processing Power and Speed:

Processing Power and Speed The human brain – At the moment we can only estimate the processing power of the average human brain as there is no way to measure it quantitatively. If the theory of taking nerve volume to be proportional to processing power is true we then, may have somewhat of an estimate of the human brain's processing power…

Human Brain vs the Processor!:

Human Brain vs the Processor!

The processor in the Human Eye!:

The processor in the Human Eye! It is fortunate that we understand the neural assemblies is the retina of the vertebrate eye quite well (structurally and functionally) because it helps to give us a idea of the human brain's capability. The retina is a nerve tissue in the back of the eyeball which detects lights and sends images to the brain. A human retina has a size of about a centimeter square is half a millimeter thick and is made up of 100 million neurons . Scientists say that the retina sends to the brain, particular patches of images indicating light intensity differences which are transported via the optic nerve , a million-fiber cable which reaches deep into the brain. Overall, the retina seems to process about ten one-million-point images per second. From http://library.thinkquest.org/C001501/the_saga/compare.htm

Estimated Processing Power of the Brain!:

Estimated Processing Power of the Brain! Because the 1,500 cubic centimeter human brain is about 100,000 times as large as the retina, by simple calculation, we can estimate the processing power of a average brain to be about 100 million MIPS (Million computer Instructions Per Second ). In case you're wondering how much speed that is, let us give you an idea. 1999's fastest PC processor chip on the market was a 700 MHz pentium that did 4200 MIPS. By simple calculation, we can see that we would need at least 24,000 of these processors in a system to match up to the total speed of the brain !! (Which means the brain is like a 168,0000 MHz Pentium computer ). But even so, other factors like memory and the complexity of the system needed to handle so many processors will not be a simple task. Because of these factors, the figures we so childishly calculated will most probably be a very serious underestimate.

The Brain and MEMORY Capacity:

The Brain and MEMORY Capacity The human brain - So far, we have never heard of anybody's brain being "overloaded" because it has ran out of memory. (So it seems as if, the human brain has no limit as to how much memory it can hold. That may not be true) Our best possible guess of the average human brain's capacity would by calculating using the number of synapses connecting the neurons in the human brain. Because each of the synapses have different molecular states, we estimate each of them to be capable holding one megabyte worth of memory. Since the brain has 100-trillion-synapses, we can safely say that the average brain can hold about 100 million megabytes of memory !!! Interesting Facts There is no sense of pain within the brain itself. This allows neurosurgeons to probe areas of the brain while the patient is awake. (Anyone watched Hannibal?) A living brain is so soft you could cut it with a butter knife. Each time you have a new thought or memory, a new brain connection is made between two or more brain cells. 4. Your brain generates up to 25 watts of power while you're awake---enough to illuminate a light bulb.

The Processor::

The Processor: Another TERM for the processor is…. CPU –Central Processing Unit This is (somewhat) like the BRAIN…all the important ‘processing’ occurs here.

RECAP:

RECAP Computer System consists of Five Main Components `. Auxiliary Storage (Permanent Storage –disks etc) 2. Main Memory (RAM or ROM?) 3. Input Devices 4. Output Devices & 5. The Processor! Main Components of a Computer

The Processor: (Structure) :

The Processor: (Structure) The ALU The CU The SC Inside the CPU Arithmetic Logic Unit –in which all arithmetic and logic Operations are carried out. 2. The Control unit …which coordinates the activities Taking place in the CPU, memory and peripherals, by sending Control signals to the various devices 3. System Clock –(interesting) –it generates a continuous Sequence of clock pulses to step the control unit through its Operation.

The ALU:

The ALU Calculations….

The CU:

The CU The Control unit is linked to a clock which generates pulses at a frequency measured in megahertz. Its purpose is to control and synchronize the way data is processed.

The System Clock:

The System Clock The CPU Clock Probably the most basic of the timed events in a PC is the step-by-step operation of the computer's CPU, whose speed is determined by the frequency of a special oscillator circuit that generates high-frequency pulses at regular intervals. This frequency is the CPU's clock speed, and it determines how quickly the CPU can carry out its functions. At each tick of the CPU clock (that is, at each pulse in the CPU oscillator's signal), the CPU carries out part of one machine instruction. All CPU instructions require one or more clock cycles to execute. From http://pheatt.emporia.edu/courses/1999/cs345s99/hand01.htm

CPU:

CPU CIRCUITRY : controlling the interpretation and execution of instructions… Registers (Special Storage locations) these hold information temporarily while it is being decoded or manipulated.

Inside the CPU:

Inside the CPU ALU CIR PC SR CU MAR R0 R1 R2 R3 MDR EXTERNAL BUS MAIN MEMORY These are the general purpose registers The MDR is often called the Memory Buffer Register (MBR) Register: An extremely fast piece of on-chip memory (usually about 32 or 64 bits in size for temporary storage of a binary value)

Each register has a specific purpose:

Each register has a specific purpose PC (Program Counter) or SCR or Sequence Register General Purpose Registers CIR –Current Instruction Register MAR –Memory Address Register MDR (MBR) Memory Data Register Status Register

Program Counter:

Program Counter Holds the address of the next instruction To be executed. It is also known as the sequence Control register (SCR) or the sequence register

Program Counter (or SCR):

Program Counter (or SCR) When a sequence of instructions is being executed.. PC is automatically incremented to point to the next instruction i.e it holds the address of the next instruction to be executed. Depending on the length of the current Instruction, 1,2,3 may have to be added to its current contents. If the CI is a jump or branch I then the address to branch to is copied from the current instruction to the program counter

General Purpose Registers:

General Purpose Registers Used for performing ARITHMETIC functions In Some computers –only one general purpose register ….called an ACCUMULATOR The accumulator acts as a ‘working area’ Other computers have up to 16 GPR’s

General Purpose Registers:

General Purpose Registers

What happens in a GPR?:

What happens in a GPR? There may be a need to add the contents of memory locations 1000 and 1001 and store result in Location 1002. What would you do?

You could break it down into the following instructions…:

You could break it down into the following instructions… Load Contents of 1000 into the Accumulator Load contents of 1001 into the Accumulator Store contents of result in 1002

CIR or IR:

CIR or IR The Instruction register holds each instruction while it is decoded by the Instruction decoder which then sends a signal to the control circuitry to enable the instruction to be executed.

What happens in the CIR?:

What happens in the CIR? As an example let's look at just one machine cycle. The first cycle in a program. The content of program counter initially 0000 0000 is placed on the address bus. The instruction in this first address is 'read out of memory' and placed on the data bus The instruction is held in the instruction register whilst it is decoded into a signal that goes to the control circuitry. This then carries out the instruction. Let us suppose the instruction was to load a number stored in memory into the accumulator. The program counter increments to 0000 0001 the contents of this address are placed on the data bus and the control circuitry loads this into the accumulator. From www.deyes.sefton.sch.uk/technology/images/A-%

CIR:

CIR LDA 1000 …………………. ………………….. ………………….. So, to load the contents of location 1000 into the accumulator: The CIR contains both the OPERATOR and the OPERAND of The current Instruction

Operator Operand:

Operator Operand LDA 1000

MAR:

MAR Holds the address of the memory location from which data will be read OR Holds the address of the memory location from which data will be written.

MAR –Memory Address Register:

MAR –Memory Address Register Remember –both instructions and data are held in memory Sometimes…MAR holds address of an instruction to be fetched Sometimes MAR holds the address of data to be used in an instruction. SO WHAT HAPPENS WHEN AN INSTRUCTION IS TO BE FETCHED?

So, when an instruction is to be fetched…:

So, when an instruction is to be fetched… The contents of the program counter are copied to the MAR so that the CPU will know where in the memory to get the next instruction from…

RECAP -6 Registers….:

RECAP -6 Registers…. PC (Program Counter) or SCR or Sequence Register General Purpose Registers CIR –Current Instruction Register MAR –Memory Address Register MDR (MBR) Memory Data Register Status Register

MDR (Memory data register) MBR:

MDR (Memory data register) MBR Used to temporarily store data read from or written to memory…… LDA 1000 (the instruction) is placed here en-route to CIR, where it will be DECODED! When the instruction is decoded, then operand 1000 is placed in the MAR And contents of location 1000 will be copied to the MDR

Important fact about the MDR::

Important fact about the MDR: ALL transfers from memory to the CPU go via the memory data register. Both the MDR and the MAR serve as a “Buffer”….to compensate for the difference in speed between CPU and memory.

SR -Status Register:

SR -Status Register Contains bits that are set or cleared based on the result of an instruction. eg. One particular bit will be set if overflow occurs, and another bit set if the result of the last instruction was negative. Based on this information the CPU could make a decision on whether to branch out of a given sequence. Status Registers……..also contain information about INTERRUPTS

END:

END Structure of the Proccessor Discuss?

Role of the Processor (CPU):

Role of the Processor (CPU) The CPU executes a program that is stored as a sequence of machine language instructions in main memory. It does this by repeatedly reading, or fetching, an instruction from memory and then carrying out, or executing, that instruction. This process -- fetch an instruction, execute it, fetch another instruction, execute it, and so on forever -- is called the fetch-and-execute cycle. With one exception, this is all that the CPU ever does. What does it do? THE CPU EXECUTES INSTRUCTIONS How does it do this? Ans: it does this by reading an instruction (fetching it) decoding the instruction And then executing it!!!!! This is called the FETCH –EXECUTE-CYCLE!!!!!!!!! Note: The CPU also supervises operations such as data transfers between I/O devices

The steps in the Fetch-Execute cycle:

The steps in the Fetch-Execute cycle Two steps… What would they be? FETCH CYCLE! And the EXECUTION CYCLE! This goes on and on forever………………Unless there is an interrupt. At the end of an execution cycle -> check for an interrupt If interrupt present, then suspend execution and pass to interrupt Handling program.

What is an Interrupt?:

What is an Interrupt?

What would interrupt the F-E cycle?:

What would interrupt the F-E cycle? An I/O device might need to transfer data…and will generate an interrupt. CPU suspends execution of the program…and transfers to an interrupt handling program. TEST FOR INTERRUPTS is carried out at the end of every INSTRUCTION Cycle.

Slide 46:

Any instructions to execute? Start Fetch next instruction Decode Instruction Execute Instruction Any Interrupts to be processed? Transfer Control to interrupt Handling program Put in the correct order.

What is a Bus?:

What is a Bus?

What is a bus?:

What is a bus?

Different Types of Busses…:

Different Types of Busses… SERIAL OR PARALLEL Data bus Address bus Control Bus

Description of Busses:

Description of Busses A control bus is (part of) a computer bus , used by CPUs for communicating with other devices within the computer. While the address bus carries the information on which device the CPU is communicating with and the data bus carries the actual data being processed, the control bus carries commands from the CPU and returns status signals from the devices, for example if the data is being read or written to the device the appropriate line (read or write) will be active ( logic zero ). From Wikipedia

Data:

Data data bus carries the actual data being processed

Control:

Control A control bus is (part of) a computer bus , used by CPUs for communicating with other devices within the computer the control bus carries commands from the CPU and returns status signals from the devices, for example if the data is being read or written to the device the appropriate line (read or write) will be active ( logic zero ).

Address Bus:

Address Bus An address bus is a computer bus , controlled by CPUs or DMA -capable peripherals for specifying the physical addresses of computer memory elements that the requesting unit wants to access (read or write). The width of an address bus, along with the size of addressable memory elements, generally determines how much memory can be directly accessed. For example, a 16-bit wide address bus (commonly used in the 8-bit processors of the 1970s and early 1980s) reaches across 216 (65,536) memory locations