3.1.4 Hardware

3.1.4 Hardware

1. 3.1.4a - The CPU

   • A computer contains a multitude of hardware including RAM, a power supply, the motherboard, hard drives and the CPU. The CPU contains the following:
     • Control Unit - Co-ordinates and controls all the operation carried out by the computer.
       • It repeats the following operations over and over:
         • Fetch - causes the next instruction to be fetched from main memory
         • Decode - produces a signal which controls the other parts of the computer such as the ALU
         • Execute - causes the instruction to be executed
     • ALU - Performs two sorts of operations on the data:
       • Arithmetic operations (+, -, *, /)
       • Logical operations (comparison, <, >, =)
       • Also acts as a conduit through which all input and output to the computer is done.
     • Memory Unit - The RAM is the location where quick and easily accessible information can be accessed by the control unit
       • Access is fast.
       • Can contain at any one point:
         • The OS
         • Software in use
         • Data software is using
       • RAM is volatile memory.

2. 3.1.4b - Registers

   • Within the CPU; alongside the ALU, control unit and memory unit, also exist circuitry that contain registers.
     • Register - An extremely fast piece of on-chip memory. Usually 32 or 64 bits in size and used for small temporary storage.
     • Many different types of registers exist, including:
       • Program Counter - Holds the address of the next instruction to be executed. This is also known as the Sequence control register
       • Memory Address Register- Holds the address in memory of the location of the next instruction to be used.
       • Memory Data Register - The contents of the MAR is copied to this. This may either be:
         • An instruction/ operation
         • The data to be used
         • The data that needs to be copied to an address
       • Current Instruction Register - Holds the instruction whilst it is being executed. The MDR contents is copied to the CIR if it is an instruction.
       • Status Register - Contains status flags that are set or cleared based on the result of an instruction
       • Accumulator - AKA General Purpose Register; used for performing arithmetic functions

3. 3.1.4c - Buses

   • The internals within a computer need a way of communicating with one another. This is what buses are used for.
     • Buses - A set of parallel wires connecting two or more components of the computer. There are 3 main types of buses used in a computer:
       • Control Bus - Carries commands and controls signals to and from every connected device.
         • Bi-directional.
       • Data Bus - Transports physical data to and from the memory.
         • Bi-directional in some cases.
       • Address Bus - communicates the address of the computer memory of the location that a requesting device wants to access
         • Uni-directional

4. 3.1.4d - Connectivity

   • Device connectivity - Connecting devices to a computer either by hard-wiring or by wireless mediums
     • Physical [Cable]: Twisted Pair, Coaxial and Fibre Optic
     • Non Physical [Wireless]: Bluetooth, Radio Signals, Satellite, WiFi, Infrared
     • Certain methods are better for certain purposes:
       • Data rate can be increased with higher quality cable
       • The number of frequencies that can be sent before interference is known as bandwidth
       • Copper has a low bandwidth and fibre has a very high bandwidth

5. 3.1.4e - Types of Main Memory

   • Random Access Memory - Used for storing programs which are currently running and the data which is being processed.
   • Read Only Memory - Non Volatile memory which is permanently etched into the memory chip

6. 3.1.4f - Secondary Storage Media

   • There are 3 main types:
     • Magnetic - Records data on magnetic disks. Mechanical parts move over the disk surface to read the data.
     • Optical - Data recorded on optical disks. Lasers are used to read and write from the disk
     • Solid State - Data is stored onto solid state memory chips. Durable and fast with no moving parts.

7. 3.1.4g - Transfer of Data

   • The 'fetchdecute' cycle also contains interrupts and buffers.
     • Buffers are used extensively in computer systems to help match the speeds of many devices
     • An interrupt is a signal form some device or source seeking the attention of the processor
       • There is a register called the interrupt register that is checked at every fetch-execute cycle and the data is acted on accordingly
       • Each interrupt is assigned a priority as is acted on according to the level of the priority

8. 3.1.4h - Peripheral Devices

   • There exist hundreds of peripheral devices that can be connected to a computer.
     • Each has certain features, advantages, disadvantages and uses.