Internal Hardware of a computer

Computers

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

Processors

• 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

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

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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

• 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.