Internal components of a computer

• The internal components of a computer system consist of the hardware required to process data and to allow the processor to communicate with other devices such as secondary storage, display screens, and printers.
• The main internal components of a computer system are:

  • Processor (CPU)
  • Main memory
  • Input/output (I/O) controllers
• The internal components of a computer system consist of the hardware required to store and process data, and communicate with external, peripheral devices.
• The main internal components of a computer system are:

  • Processor
  • Main memory
  • Input/output (I/O) controllers
• These components are connected by the system bus, which is made up of the address bus, data bus, and control bus.
• Other types of memory are crucial for the operation of a computer system. Secondary storage (e.g. SSD, HDD) provides permanent storage for programs and data. 
• The processor, sometimes referred to as the CPU (central processing unit), is the part of the computer that processes data by executing program instructions. At processor level, these will be low-level instructions in the form of machine code that the processor has been designed to handle, based on a specific processor instruction set.
• For the processor to be able to execute a program, the program instructions need to be transferred from secondary storage into main memory from where they can be fetched, decoded, and executed. The data that needs to be processed is also loaded into main memory (from secondary storage) or provided by the input and output devices via the I/O controllers.
• Main memory is memory that can be accessed directly by the processor. Each memory location, where instructions or data are stored as binary sequences, has a physical address, which is a number used to locate that memory location and access its contents.
• There are two main types of main memory:

  • RAM, which is the working memory that is used by the processor during the fetch-decode-execute cycle
  • ROM, which is used in the boot process for the computer system
• Main memory is distinct from secondary storage, which the processor can't work with directly. Secondary storage must be accessed through I/O controllers. You can read more about main memory on this concept page which also covers cache, registers, and virtual memory.
• All external (peripheral) devices are connected to the processor through I/O controllers. These provide the mechanism for:

  • input data to be received for processing from input devices, such as keyboards
  • the results of computation to be output from the system to output devices, such as display screens
• Secondary storage devices are also connected to the processor through I/O controllers. Secondary storage, in contrast to main memory, cannot be accessed directly by the processor. It is not favourable for peripheral devices to be directly attached to the processor. Each device operates in a different way, at different speeds, and using different electronic signals. An I/O controller can be described as an interface between the core computer system and its peripherals.
• I/O controllers provide a set of addressable registers that the processor (CPU) can access to communicate with the I/O devices. For example, the characters entered using a keyboard would be stored in an I/O controller that the processor (CPU) can access and process, such as displaying the characters on a screen.
• Physical port


  e.g. a USB port used to connect a keyboard to a computer, provides a connection for the peripheral
• Peripheral device


  • Has a cable or connector to connect it to the port
  • Operates at a much slower speed than the processor
• I/O controller circuitry


  1. Facilitates the exchange of data in the form of electrical signals between the processor and the peripheral

  2. Translates the signals into the correct form
• Interface


  Provides a buffer so that the disparate timing requirements can be satisfied
• Each peripheral device can have its own I/O controller or can share a hub controller (as is the case with USB). Large desktop computers usually have slots where additional specialist controllers can be added.
• Device driver


  A piece of software that provides a software interface for the peripheral device, which enables the operating systems to access the functions of the hardware without having to be configured specifically for every device that is used
• Plug and play devices


  • The driver is either embedded or automatically downloaded when the hardware is connected
• Bus


  A communication system that is used to transfer data between components
• Types of buses


  • System bus
  • External buses
• System bus


  A set of parallel connections that allow internal components to communicate with each other and exchange data
• External buses


  Used to connect the peripherals to the processor, can be serial or parallel connections
• Bus implementation


  Wires, electronic pathways, and tracks on printed circuits
• Von Neumann architecture system bus

  • Address bus
  • Data bus
  • Control bus
• System bus connections


  Connects the processor (CPU), main memory, and the I/O controllers
• Input device I/O controller

  One-way connection towards the data bus
• Output device I/O controller

  One-way connection from the data bus
• Secondary storage device I/O controller

  Two-way connection from the data bus
• Processor


  One-way connection towards the address bus
• Address bus


  One-way connection towards all other components (main memory and I/O controllers)
• Main memory


  • Two-way connection with the data bus
  • One-way connection with the address bus
• Each bus consists of a set of parallel — not single — lines
• Data bus

  Used to transfer data and instructions
• Data bus

  • Bidirectional, allows two-way connection between internal components
  • Allows values to be written to or read from a location
• Data transfer


  1. To and from the processor

  2. To and from main memory

  3. To and from the I/O controllers
• Width of the data bus


  Number of parallel lines, determines the number of bits that can be transferred in one operation
• The width of the data bus is typically 8, 16, 32 or 64 bits.