Hardware & Data transmission

Hardware & Data transmission

1. Central components of a computer system

   • CPU
     • Control unit
       • Fetch
         • Decode
           • Execute
             • Causes the instruction to be exicuted
           • Produces signals which control other parts of the computer such as the ALU
         • causes the next instruction to be fetched from, the main memory
     • Arithmetic Logic Unit
       • ALU : Performs two sorts of operations on data
         • 3) Acts as a conduit through which all I/O to computer is done (Gateway to the processor)
         • 1) Arithmetic operations (addition, subtractions, multiplication, division)
         • 2) Logical operations (comparing one data item to another, is it smaller, greater, equal to)
     • Registers
       • Special storage locations called registers are included in this circuitry to hold information temporarily.
       • Registers: An extremely fast piece of on-chip memory, usually 32 or 64 bits in size for temporary storage of a binary value.
     • • Program Counter : Holds the address of the next instruction to be executed. It is also known as the sequence control register (SCR) or the sequence register.
       • Memory Address Register : Holds the position / address in memory of the location containing either: The next piece of data to be read or The next instruction to be used
       • Memory Data Register : The contents of the address specified in the MAR are copied to the MDR. This may be either: An instruction / operation or The data to be used (with an instruction) or Data to be copied to an address Both the MDR and the MAR serve as ‘buffer’ registers to compensate for the difference in speed between the CPU and memory.
       • Current Instruction Register : Holds the instruction while it is being decoded/executed.
       • Status Register : Contains “status” bits or flags that are set or cleared based on the result of an instruction.
       • Accumulator : The accumulator or “General Purpose Registers” as they are often called are used for performing arithmetic functions
   • Memory Unit
     • The Memory Unit, often referred to as main memory, primary memory, central memory, core memory, is the location where quick and easily accessible information can be read from and written to by the Control Unit.
     • Access is very fast
       • At any one time it has inside it
         • The Operating System (or part that is currently in use)
         • The data which the software is using.
         • The software currently in use

2. Buses

   • A bus is a set of parallel wires connecting two or more components of the computer
   • the CPU is connected to the main memory by 3 separate buses
     • Data bus: the data in that location is returned to the CPU on this, it transports actual physical data in the form of bits and bytes of information ti and from memory
     • Address bus: used when the computer wishes to access a particular memory location it sends this address to the main memory, communicating the physical addresses of computer memory
     • Control Bus: control signals are sent along this to and from every single connected device

3. Device connectivity

   • physical
     • Copper: Twisted Pair
     • Copper: coaxial
     • Fibre Optic
   • Wireless
     • Infarared
     • Bluetooth
     • WiFI
     • Other Radio Signal
     • Satellite
   • The effectiveness of the means of communication Can be measured in the rate at which data can be transmitted along the medium: the bits per second or baud rate. Data rate can be increased by using higher quality cable with less attenuation or sending more than one signal at a time or increasing the frequency at which data is sent. Each signal can be sent on a different frequency or wavelength. The number of frequencies that can be used before they interfere with each other is known as the bandwidth. Copper has a low bandwidth, wireless higher bandwidth and fibre very high bandwidth. High frequencies attenuate more quickly which reduces the number of frequencies that can be used with copper.

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