4.7

4.7

1. Internal componetns

   • Processor - Fetches and executes instructions
   • Main Memory - Stores instructions and data for the processor to use
     • Main memory is addressable memory. It is split into sections with each section given an adress. These can be read or written in by the processor
     • Machine code instructions are stored in the main memory are then fetched and exectured serially by the processor that performs arithmatic and logic operations
   • Adress bus - Stores and transfers adresses between the processor, main memory and controllers
     • The address bus is UNIDIRECTIONAL (addresses are only transfered from the processor to the main memory and controllers) Specifies a memory or controller address that can be used
   • Control bus - Carries control signals between the processor, main memory and controllers
     • BIDRECTIONAL (data sent either direction) The control bus sends control signals between the controllers, main memory and processor - Sends signals such as: putting the memory in read or write mode
   • I/O controllers- interface with input/output devices
   • Data bus - Carries data signals between processor, Main memory and Controllers
     • BIDRECTIONAL
   • The busses - Busses are just wires and connections to allow communication between the processor, main memory and controllers

2. Architecture

   • Von nuemann - Used for general purpose systems - Faster and easier to manufacture. Instructions (programs) and data are stored in the same main memory Instructions and data cannot be fetched at the same time meaning to complete one execution it takes 2 clock cycles
   • Havard - Used for embedded systems such as signal generator. It is more expensive to manufacture. Instructions (programs) and data are stored in different memory. Data and instructions can be fetched at the same time meaning to complete one execution.

3. Structure of the processor

   • ALU - performs maths and logical opretaions
   • Control Unit - Fetches the next instruction and decodes it
   • Clock - sends regular signals to the control unit that dictate the speed at which it decodes and executes instructions
   • General purpose registers - Storage areas of data whilst an instruction is being executed
   • Dedicated registers
     • Program register (PC) stores the memory address for the next instruction to be fetched
     • Memory address register (MAR) stores the memory to be read or written
     • Memory buffer register (MBR) contains the the information that has been read/ to be written
     • Current Instruction register (CIR) Contains the current instruction that is being executed
     • Status register - Contains information about the proccessor, such as if there has been an overflow
   • Fetch Execute Cycle
     • Fetch: Value in the PC is copied the MAR. Then the value in the MAR is saved to the MBR. This is then copied into into the PC, the PC is incrimented.
     • Decode: The data is split into operand and opcode
     • Execute: Any of these can happening; The operands are sent to the ALU for processing, the status register is updated and the PC is updated with the next instruction's memory address

4. Machine code

   • Opcode- The instruction from the processor's instruction set
   • Operand - values or memory address that the opcode's intrsutction applies to
   • Opcodes include addressing mode: Immediate addressing - The operands value is the data. Direct Addressing - The operands value is the memory address for the data
   • Each processor has an instruction set which is just instructions it is capable of performing: such as, Add, Store, Halt, ETC
   • Interupt - Used to pause the current program and run a high priority routine
     • An interrupt service routine - IRS - when the hardware requests an interrupt to the processor
     • Memory and registers are backed up during interrupts and restored when complete

5. Processor performance

   • Clock Speed
     • The clock sends a regular signal to the control unit which tells it when to fetch and execute the next instruction. A faster clock speed means more instruction executed/fetched per second. Most modern computers have a clock speed of 3-4GHz. Clock speed is limited by the processing speed and the heat output. Each instruction executed causes some heat to be generated and therefore it needs to be dissipated
   • Cache size
     • The processor has a small amount of memory inside it called Cache. This stores the most frequently used instructions so a larger cache means more instructions can be stored and fetched from the quicker, closer cache rather than having to fetch from the main memory which would take longer
   • Number of cores
     • A core is a processing unit. Tasks can then be split up and instructions can be complete by each core at the same time. This means more cores can complete more instructions at once as they can run more instructions simultaneously. However this doesn't affect the speed of some tasks as they might be linear meaning for one instruction to be executed, it needs the result of the previous instruction.
   • Word lenght
     • Word length is the amount of bits that can be processed at once. More bits being processed in one clock cycle
   • Address bus width
     • address bus width is the amount of connections on the bus. A larger width means more memory can be addressed in one clock cycle
   • Data bus width
     • Data bus width is the amount of data that can be transferred from the memory to the processor in one clock cycle so a larger width means more data per cycle and therefore faster

6. Secondary storage: Unlike main memory, It is cheap, non-volatile and slow. Data is copied to main memory prior to a taskand then copied back to secondary storage after it is complete

   • Magnetic Hard Disk: A spinning disk with magnetic particles who's polarisation can be changed to represent either 1 or 0. This is very slow due to moving parts, noisy and power-hungry. Typically 1-3TB
   • Optical disk: A reflective surface with sections that are punched to stop the reflections. A laser is then pointed at the surface and a detector will then know if its a 1 or 0 based on if there is a refelection. Cheap, easy to damage
   • SSD: Uses NAND Flash Memory and a controller that manages writing. Based on floating gate transistors that trap and store charge. Data cannot be overwritten easily as whole blocks must be deleted and re written. The controller combats this by spreading the data around all of the available flash memory. Faster than other Secondary Storage but more expensive. Typically 250gb-1tb

7. External hardware devices

   • Barcode reader
     • Laser scans across a series of black and white stripes. The amount of light reflected determines if it was a black or white stripe and the width of the stripe has a value which relates to a product database
   • Digital camera
     • light is focused through a lens onto a CSMOS sensor which has an array of pixels with a red blue and green filter. Each pixels creates a voltage proportional to the amount of light hitting it. These RGB values are then used to create the color
   • Laser printer
     • Static electricity is generated on a drum and paper is wrapped round it. Then a laser is used to dissipate the static electricity in a particular pattern. Toner powder is then put on the drum and sticks to the parts that have static. The toner is then heated and fused to the papre.
   • RFID
     • A small microcontroller with large antenna is embedded into a tag. radio frequency induces enough current in the antenna to the power chip. The chip reads the data in the frequency and transmits a response