1.1

1.1

1. Architecture of the CPU

   • it processes data
   • processors can be multicore
   • executes instructions
   • has a clock speed measured in hertz
   • `brains` of the computer
   • Control Unit
     • In control of the CPU
     • Manages the F-D-E cycle
       • Fetch - Copy memory addres from PC to MAR
         • Copy instruction in MAR address to MDR
         • Increment the PC
         • Decode - CU decodes the instruction in the MDR
           • CU then loads next MAR/MDR values
             • Execute - The instruction is performed:
               • Load data from memory
                 • Write data to memory
                   • Do a calculation/logic operation
     • controls the flow of data inside and outside the CPU
     • Contains the PC
   • Arithmetic Logic Unit
     • Does all the calculations
       • subtraction
       • division
       • multiplication
       • compares numbers
       • addition
     • Logic operations (AND, OR, NOT) and binary shifts
     • Contains the accumulator
   • Cache
     • Very fast memory
     • Stores regularly used data
     • Very low capacity
     • Three levels
       • L1 is quickest but smallest
       • L3 is biggest and slowest
   • Registers
     • MAR
       • holds any memory address about to be used by the CPU. May point to data or an instruction
         • Memory Address Register
     • MDR
       • holds the actual data or instruction, fetched from or waiting to be written to memory
         • Memory Data Register
     • ACC
       • stores intermediate results of calculations in the ALU
         • Accumulator
     • PC
       • Program Counter
       • Holds the memory address of the instruction for each cycle
   • Buses
     • a series of lines that connect the processor to another part of the computer, e.g. cache memory, main memory.
     • Address Bus
       • Uni-directional
       • passes an address from the CPU to RAM.
     • Data Bus
       • Bi-directional
       • carries data to main memory from the processor and vice versa

2. CPU Performance

   • Clock Speed
     • number of instructions a single processor core can carry out per second (Hz)
     • higher clock speed = more instructions carried out p/s
     • Some CPUs can be overclocked to make them run at a higher clock speed, but its risky if done wrong
   • Number of Cores
     • Each core in a CPU can process data independently
     • The more cores a CPU has, the more instructions it can carry out at once
     • Most PCs and smartphones have 4 or more cores
   • Cache Size
     • Cache is data storage inside the CPU thats much faster than RAM
     • A larger cache gives the CPU faster access to more data it needs to process

3. Embedded Systems

   • Computers built into other devices
     • E.g. dishwashers, microwaves, TVs
   • Often used as control systems
     • They monitor and control machinery
       • In a dishwasher the embedded system could control the water pumps
         • and control the thermostat to keep the water at an appropriate temperature
           • and water, release mechanisms, manage the various dishwasher cycles
   • Usually dedicated systems
     • This makes them easier to design, cheaper to produce and more efficient
       • at doing their task than a general purpose computer