Hardware and Software

Hardware and Software

1. Internal Components

   • 3 main components

2. Processor

   • Consists of Control Unit (CU), a series of Registers and the Arithmetic Logic Unit (ALU)
     • Control Unit is a digital circuit that co-ordinates the movement of data, sequencing of instructions and directs the operation of the other components of a computer system by providing control and timing signals
       • Timing Signals
         • Provided by an internal clock which helps to synchronise the operation of the internal components
         • CPU needs a certain number of clock ticks to carry out each instruction. Clock speed is expressed in megahertz (MHz) or gigahertz (GHz)
     • ALU is digital circuit forms part of the processor. Carries out mathematical and logical operations on data associated with instructions being executed
     • Registers
       • High speed memory location forming part of the processing unit
       • Types of registers
         • Program Counter (PC)
           • Stores the address/location in memory of the next program instruction to be executed
           • As soon as the instruction has been fetched from memory the contents of the PC are incremented to ensure it points to the next location
         • Memory Address Register (MAR)
           • Stores the address of a memory location to be accessed either for a data/instruction read or write
         • Memory Data Register (MDR)
           • Stores data that has just been fetched from memory or data waiting to be stored/written to a location in memory
         • Current Instruction Register (CIR)
           • Stores the instruction currently being executed by the processor

3. Memory

   • Internal Memory
     • Memory used by the processor in the execution of instructions
   • Main Memory
     • Referred to as RAM or Random Access Memory
       • Referred to as RAM because the processor can go directly to any location to access an item of data; it does not have to access the memory locations in a particular (sequence) order.
     • Is volatile
       • When the power is removed from the system the data will be lost
   • Cache Memory
     • A form of RAM which can be accessed by the processor at a faster rate than main memory
     • High speed volatile memory that is often integrated into the processor chip
     • Used to store copies of the contents of the most frequently used memory locations

4. Buses

   • Communication systems known as buses are used to support the transfer of signal between the internal components of a computer system (internal buses)
   • Allows for communication with various input and output (I/O) devices used for communication
   • A set of physical connections in the form of set of physical cables or printed circuits used to connect the various hardware components used in execution of instructions
   • Types of buses
     • Address Bus
       • The location may be accessed to read data from or write data to memory
     • Data Bus
       • Allows for the transfer of data between one component of a processor or computer system and another
     • Control Bus
       • If an item of data is to be stored in memory the control bus will carry the write command tot he memory location

5. Ports

   • How data can be transferred from the input/output devices to the internal components of the computer
   • Allows data to be transferred from peripheral devices hey must be connected to the computer via an Input/Output port. The 3 ports are:
     • Serial Port
       • One bit at a time across a single wire
     • Parallel Port
       • Multiple bits of data across multiple wires
     • USB (Universal Serial Bus)
       • Provide a high speed serial connection to most types of peripheral devices

6. Fetch Execute Cycle

   • 1.Start
     • 2.Load address into PC
       • 3.Copy PC to MAR
         • 4.Increment PC
           • 5.Load data into MDR
             • 6. Transfer data to CIR
               • 7. Executive instruction in CIR
   • Process used by a computer to retrieve a program instruction from memory
   • Address of first instruction to be read is loaded into the PC

7. Factors influencing the speed of processing

   • Clock Speed
     • If CPU requires a specific number of clock ticks to execute an instruction then by increasing the clock rate (number of clock ticks/cycles per second) we can increase the number of intructions executed per second i.e the faster the clock speed the more instructions the CPU can execute per second
   • Cache size
     • Increasing the speed of access to a greate rnumber of frequently accessed instructions and data items can help to increase the speed of operation of the processor
   • Processor Type
     • Reducted Instruction Set Computer
       • Smaller number of insturctions at its disposal during processing
     • Complex Instruction Set Computing
       • In complex processing tasks, RISC processing units have to combine many simple insturctions to complete each task meaning an increased number of fetch-execute cycles need to be completed to carry out complex tasks, thus slowing down the overall speed of processing