1.1 Processors and devices

• Parts of Von Neumann architecture

  ALU

  CU (decodes and executes instructions)

  RAM (Stores data and programs)

  Address bus (transmits addresses of both data and instructions)

  Data bus (both data and instructions)
• Order of the FDE cycle (with registers)

  Fetch: Address for next instruction is copied from PC to MAR

  Decode: Contents of memory address in MAR copied to MDR (PC incremented)

  Contents of MDR copied to CIR

  Contents of CIR split into opcode and operand

  Execute: Execute instruction
• What is the Von Neumann bottleneck


  The problem where, as data and instructions are sent along the same bus, instructions cannot be sent at the same time as data
• What in Harvard architecture is different to Von Neumann


  Separate RAM for instructions and data

  Uses separate busses to transmit data and instructions making it faster than Von Neumann

  Comparitively more expensive
• What factors affect CPU performance

  Clock speed

  Address bus width

  Number of cores

  Cache

  Pipelining

  Memory
• Clock speed and Overclocking

  Clock speed is the number of clock cycles completed per second

  Overclocking is setting your clock speed above official speed grade

  Modern CPUs change speed based on processes
• What is the benefit to more cores

  Each core processes independently leading to completing instructions in parallel

  Dramatically improves performance while keeping CPU small (fits in socket and easy to cool)
• Why and how is cache used

  Anticipates commonly used data and instructions and keeps them in cache, which can be accessed quicker

  3 levels of cache with L1 being smallest and quickest
• What features may modern CPUs have

  Multiple cores

  Cache

  Instruction and data cache (similar to harvard)

  Pipelining
• What is Pipelining and why is it useful

  Makes progress on multiple task simultaneously

  While one instruction is being fetched, another is being decoded, and another executed

  Increases throughput by making CPU usage more efficient
• What are Bubbles and Flushing in relation to Pipelining

  A processor may deal with delays by stalling, which leads to multiple cycles of nothing happening which is known as a bubble

  When a branch instruction is executed, it invalidates all prior stages in the pipeline which need to be cleared
• What is CISC

  Complex Instruction Set Computers

  Uses a large instruction set to complete tasks in as few lines of assembly code as possible
• What is RISC

  Reduced Instruction Set Computers

  Minimum number of small instructions that take a single clock cycle to complete
• Is LMC complex or reduced

  LMC is a reduced instruction set [LDA, STA, ADD, SUB]
• What are the benefits and uses of CISC

  Less complex code

  Smaller code

  Less RAM required to load

  More addressing modes

  Used in laptops and desktops
• What are the benefits and uses of RISC

  One instruction takes one cycle (pipelining possible)

  Less complex processor circuitry needed

  Lower power consumption

  Cheaper than CISC

  Used in smartphones and tablets
• Benefits of Parallel Processing

  Performance increase in Graphics or other parallel tasks

  Multi-core could mean if one core is stuck, the others absorb the load

  More task can be completed in the same time frame

  Faster response for time critical systems
• Detriments of Parallel Processing

  Some tasks cannot be done in parallel (binary search)

  Overhead due to coordinating threads between cores (potential slow down if processor is not completing threads)

  More costly as more expensive/sophisticated hardware required

  Can lead to deadlock
• Differences of GPU compared to CPU

  Large number of simple cores (100s)

  Instruction set specialises in mathematics

  Connects directly to graphics card

  Cant function independently

  Single instruction multiple data (SIMD)
• What is a multicore system

  A system that has more than one processing unit that can work independently of each other simultaneously
• What sensors are used for what metric

  GPS - determines geographical location

  Magnetometer - a digital compass (Points north)

  Altimeter - shows ascension or descension

  Accelerometer - measures accelerative forces

  Gyroscope - measures rotation

  Thermistor - a resistance thermometer

  Actuator - Takes in energy and turns it to motion
• How does magnetic storage work

  Data is stored by very small magnetised dots

  Data cannot be truly erased

  Hard disk platter spins and read/write heads move across platters

  The heads move across and magnetise and de magnetise where necessary
• How does optical storage work

  Data is stored using pits and lands which are pressed or lasered into the surface of the disk

  Read using lasers that convert pits and lands to zeros and ones
• How does SSD work

  Uses floating gate transistors that are hit with a charge to represent zeros and ones

  Stores data using non-volatile flash memory chips
• Benefits of SSD

  Read/write speed of 550MB/s (fastest)

  Smaller in size and weight than HDD

  No noise

  More reliable and better choice for laptops (No moving parts)
• Why choose HDD over SSD

  Cheaper to buy

  Easier to get larger amounts of storage

  Easier to recover data if damaged
• Benefits of optical storage

  Extremely portable

  Cheap to acquire

  Easy to burn a disc
• Detriments of optical storage


  Very fragile

  Stores low amounts of data

  Can be easily damaged
• What is virtual storage


  Storage that appears to be local but is physically located elsewhere (e.g network drive, cloud)
• Benefits and drawbacks of network based virtual storage

  Benefits:

  No third party involved

  Can be shared with many people

  Drawbacks:

  Expensive to buy hardware

  If the network goes down, drive is inaccessible
• Benefits and drawbacks of cloud storage

  Benefits:

  Cheaper than physical storage

  Accessible anywhere with an internet connection

  Drawbacks:

  Slow if connection is poor

  Privacy may be an issue if provider is unreputable
• Features of ROM only

  Read only memory

  Small capacity

  Non-volatile

  Stores BIOS

  (Embedded OS likely to be stored in the BIOS)
• Features of RAM only

  Random access memory

  Used to store programs currently in use

  Write speed much faster than ROM

  Faster to access than secondary storage

  Volatile

  Larger than ROM

  DRAM - used for main memory

  SRAM - used for cache and is quicker
• Features of both RAM and ROM

  Both primary storage/main memory

  Both can store programs

  Both connected to CPU via buses
• What is BIOS and its steps

  Basic Input/Output System

  Power On Self-Test (POST) runs to determine hardware is working correctly

  Loads configuration settings (clock speed, enabled interfaces)

  Finds and runs bootloader from secondary storage