Internal Hardware of a computer


Computers and Processors


  • A computer is any machine or device that processed data.
  • It is implied that the machine is electronic or digital


  • A device that carries out computation on data by following instructions, in order to produce an output.
  • Instructions can come from a useer, hardware or software.
  • In theory, a 3GHz processor could process 3000 million instructions per second
  • Generallty the higher the clock speed of the processor the faster it will carry out instructions but there are other factors which can affect performance
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Main Memory and RAM

Main Memory

  • Stores data and instructions that will be used by the processor
  • Fetches the instructions and data it needs from memory, decodes the instructions and executes them (all done one instruction at a time).

RAM (Random Access Memory)

  • Temporary storage that can be accessed quickly
  • Physically RAM is a chip or series of chips on which data is electronically stored
  • It is made up of millions of cells, each of which has its own unique address
  • The processor the needed cell by referencing the address
  • RAM is volatile
  • When a program is run on your computer it is loaded from the secondary storage to RAM
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ROM (Read Only Memory)

  • Unlike RAM it is not volatile
  • Users can not alter the contents of ROM as it is read only (though you have programmable ROM used in memory sticks, SSD etc.)
  • Traditionally we talk about ROM when referring to the BIOS which stores a limited number of instructions relating to the set up of the computer
  • BIOS is responsible for checking hardware devices are plugged in and it loads part of the operating system.
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Addressable Memory

  • Memory is made up of millions of addressable cells
  • Each memory cell has a width measured in bits
  • Each address can be uniquely addressed
  • It is the processors job to retrieve each instruction and data item in a sequential manner.
  • Different programs are stored in different parts of the memory in blocks
  • Memory maps can show which programs are stored at whichaddress- the address is normally shown in a hexadecimal format.
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  • Three buses are: Address, Data and Control
  • They are parallel microscopic wires that connect the processor to the various input and output controllers being used by the computer
  • Theya re also used to connect the internal components of a microprocessor known as registers and connect the microprocessor to memory.
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Data Bus

  • Transfers data/instructions between the processor and memory
  • Also data to and from the I/O controllers
  • Connects the registers to each other and to memory
  • Amount of data that can be carries along the bus depends on the number of wires
  • Large data items will need to be split into smaller parts to be transmitted (one sent after the other)
  • The bigger the data bus the moren data that can be transmitted in a single clock cycle.
  • The size of the data bus width is key in the overall speed and performance of the computer
  • Word Length- The number of bits that can be addressed or manipulated as one unit.
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Address Bus

  • One direction- from the processor into memory
  • Carries the memory address of the next instruction or data item
  • Opens up the location so that the contents can be placed on to the data bus or copied from the data bus
  • Size is also measured in bits and represents the amount of memory that is addressable
  • 8 bit bus would give 256 directly addressable memory cells.
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Control Bus

  • Bi-directional bus which sends control signals to the registers, the data and the address bus.
  • Its job is to ensure that the correct data is travelling to the right place at the right time
  • It involves the synchronisation of signals and the control of access to the data and address buses which are being shared by a number of devices.
  • A signal could indicate the direction of data being transmittd, whether it is reading to or writing from an I/O port.
  • Also carries the pulses being delivered by the system clock.
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Input/Output (I/O) Controllers

  • The processor needs to send and recieve instructions and data to I/O devices connected to the computer.
  • These devies are typically connected by external ports.
  • Controllers consist of their own circuitry that handles the data flowing between the processor and the device.
  • Each device needs its own controller (e.g. keyboard controller)
  • I/O controllers translate signals from the device into the format required by the processor
  • This means that you can add new devices without having to redesign the processor.
  • The controller also buffers data as the devices respond slower compared to the processor.
  • This means the processor doesn't have to wait for the individual device to respond
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Von Neumann and Harvard Architectures

  • Von Neumann- a technique for building a processor where data and instructions are stored in the same memory and accessed via buses
  • Harvard- a technique for building a processor that uses seperate buses and memory for data and instructions. It is used on embedded systems such as mobile phones, burglar alarms etc.
  • Harvard Advantage- instructions and data are handled quicker as they don't share the same bus. So programs are executed faster and more effectively.
  • Many devices use DSP (Digital Signal Processing) to take continuous and real world data such as audio or video and then to compress it to enable faster processing.
  • Chips that are optimised for DSP tend to have much lower power consumptions so are ideal for mobile phones.
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