Computer Science 1 Systems Architecture

• What is a general purpose computer


  A computer that is designed to be able to carry out many different tasks
• What can a general purpose computer do

  -Access the internet

  -browse the World Wide Web

  -store and retrieve data

  -communicate via email and social media
• What is an application


  Software program that allows user to perform specific tasks.
• What type of computer has lots of applications

  General purpose computer
• Name some types of general purpose computers

  Tablets

  Smartphones

  Games console

  Media systems in cars
• What do general purpose computers consist of

  Hardware and software
• What is hardware


  The physical components of a computer. e.g - the cpu,motherboard ,monitor,hard disk,keyboard and mouse
• What is software


  The programs that run on a computer
• Describe the flow of data within a computer

  Data is input, processed and then either output or sent to secondary storage

  It is held in primary memory whilst being processed
• How does the CPU have a role in flow of data

  The CPU receives instructions and data from an input or memory

  The instructions and data are processed by the CPU and the results are either sent to an output or transferred to secondary storage
• Describe and give examples of an input device

  A device used to input data or info into a computer e.g keyboards,mouse,camera and scanner

  Input devices take real world data and convert it into a form that can be stored on the computer. The input from these devices is processed and the computer will generate outputs
• Describe and give examples of an output device

  A device used to output data or info from a computer e.g monitor,printer or speaker
• What is the purpose of the CPU

  it processes data and controls the flow of data between the computer's other units

  Controls the rest of the computer system

  Executes programs

  Manages rest of hardware
• What is a processor

  A special component that processes data and instructions to control other components within the computer

  Two main types= CPU and GPU
• What is primary storage

  The memory in which the computer can store the data or instructions that are currently in use
• What are the two main types of primary storage

  RAM and ROM
• What is secondary storage

  The memory in which the computer can store the data or instructions not currently in use
• Name some types of secondary storage

  Hard disk drive

  Solid state drive

  Compact disk

  Flash(USB drive)
• What does the Von Neumann architecture describe?

  A system where the CPU runs programs stored in memory. Programs consist of instructions and data which are stored in memory addresses. Data would move between the memory unit and processor
• What is cache memory

  Is very fast memory, close to the CPU, used to temporarily hold data or instructions that are likely to be needed again by the processor in the course of running a program
• What does the processor (CPU) contain

  Control unit

  Arithmetic Logic Unit

  Registers
• Name the registers in the CPU

  Program Counter

  Accumulator

  Memory Address Register

  Memory Data Register
• What does the Control Unit do

  Uses electrical signals to control flow of data in the CPU. It directs and coordinates most operations.

  -fetches,decodes and executes instructions

  -sends and receives control signals to and from other devices within the computer. These control signals control hardware

  -regulates and controls processor timings using regular pulses from the system clock
• What does the Arithmetic Logic Unit (ALU) do?

  Performs arithmetic(addition,subtraction) operations

  Logic(Boolean -AND,OR,NOT) operations

  Comparison and shift operations

  -acts as a gateway between primary and secondary storage. Data transferred between them passes through the ALU
• What are the registers in the CPU?

  Very fast memory locations(small amounts of high speed memory) contained in the CPU. They are used by the processor to store small amounts of data that are needed during processing and for the execution of instructions e.g address of the next instruction to be executed, current instructions being decoded and results of calculations
• What does the Program Counter do

  Holds the memory address of the next instruction to be processed

  Holds memory address of next instruction to be fetched from memory
• What does the MAR do

  Holds the address(location in memory) of the current instruction or piece of data to be fetched/stored
• What does the MDR do

  holds data or a program instruction temporarily when it is fetched from memory or is to be sent to memory

  Holds the contents found at the address held in the MAR or data which is to be transferred to primary memory
• What is the Accumulator

  A special purpose, memory location in which results of operations carried out in the ALU are temporarily stored

  Holds the data being processed and the results of processing

  Holds the result of calculations/operations performed by the ALU
• What are buses


  A channel of communication used to transport data and instructions in the CPU
• How does cache allow for faster processing

  Cache is high speed RAM built directly within the processor. It is used to temporarily hold data and instructions that the processor is likely to reuse. This allows for faster processing as the processor does not have to wait for the data and instructions to be fetched from RAM

  Data can be transferred to and from cache memory more quickly than from RAM
• What are the different levels of cache

  The more cache memory, the faster a computer runs. However, because of its high speed performance, cache is more expensive to build than RAM so tends to be small in size

  L1 cache= small,most frequent instructions stored and has extremely fast transfer routes

  L2 cache=bigger,less frequent instructions stored and has lower speed
• What is the fetch-decode-execute cycle?

  The process that the CPU uses to retrieve and execute instructions

  The journey followed by a processor to process instructions
• Describe the fetch stage of the FDE cycle

  1. The memory address held in the program counter/PC is copied into the MAR

  2. The address in the PC is then incremented to point to the next instruction that will be needed when the cycle starts again. The PC now holds the address of the next instruction to be fetched

  3. Instructions stored at the location held by the MAR is copied to the MDR
• Describe the decode stage of the FDE cycle

  The CU decodes the instruction and sends out control signals to the component within or outside the CPU that needs to act
• Describe the execute stage of the FDE cycle

  The operation indicated by the instruction is performed by the appropriate component e.g ALU performs the operation given by the control unit
• What factors affect CPU performance

  Clock speed

  Cache size

  Number of cores
• What is the clock inside a CPU

  A clock is used to coordinate all of the computers components. The clock sends out regular electrical impulses which synchronises all the components
• What is clock speed and how does it affect performance

  Clock speed is the speed of a computer's CPU measured in hertz. This indicates the number of fetch decode execute cycles that can run per second

  The frequency of the pulses is known as clock speed(measured in hertz)

  The higher the frequency, the more instructions can be performed in any given moment of time
• What is overclocking


  When CPU clocks are slightly sped up this is known as overclocking. Overclocking can cause long term damage to the CPU, as it is working Harding and produce more heat

  One clock cycle per second=1Hz

  One billion clock cycles per second=1GHz