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Hardware and communication


The CPU is the brains of the computer and carries out all of the mathematical and logical operations to execute instructions given by the user. It is made up of many key parts which work together to execute the instructions. The processor requires software to perform actions. Hardware is the physical components that make up the computer. Software are programs and data that is used to make the hardware perform a specific task for a useful output.

This topic covers:


  • Hardware and communication

  • Memory types & caching

  • Parallelisation

  • Fetch-decode-execute cycle

  • Input & output devices

  • Dictation systems

  • Secondary storage devices




Components of a processor


Arithmetic logic unit

– Responsible for calculations, such as floating point multiplication & integer division and logical operations, with comparison tests. It also act as as a conduit for input and output both to and from the processor


Control Unit

– manages the execution of machine code through sending signals to the rest of the computer. This is possible as control signals are sent through a control bus to connected devices, like a graphics card. It also uses the processors internal clock to synchronise instructions, based on the clock speed, which is the amount of ‘ticks’ the clock does per instruction. It fetches each instruction and decodes it in the fetch-decode-execute cycle.



– circuits that link all the components within a computer together and therefore helps them work together. It also carries data, addresses and control signals to the CPU. There are 3 types of bus:



Data Bus:

carries data between components by carrying a copy of the data that is being processed. It is also used in conjunction with the address bus

Control Bus:

used to carry signals between components of the CPU, so coordinates the activities within the CPU

Address Bus:

carries address information (indicates the memory location to read/write data to) from the CPU to the memory unit.


Fetch - decode - execute cycle


Registers – A small block of memory that is utilised as a temporary storage for currently executing instructions. Its speed is limited by the processor and therefore runs at the same speed. Machine code instructions require a register to be executed.


Special purpose registers are crucial to how the processor works and values are loaded out and in of registers during execution. The main ones are the accumulator, the memory address register, the current instruction register and the program counter. General purpose registers are used as the program is ran, to enable calculations to be made and are used for many different purposes.



Program counter – stores the memory address of the next instruction that is to be executed, which is incremented after each instruction, but can be altered. This controls the order of the instructions to be executed and retrieved.



Memory Data Register – stores the fetched instruction/data


Memory address Register – stores the address of the instruction/data to be fetched


Current Instruction Register – stores a copy of the currently executing instruction


Pipelining – the processor always attempts to fetch an instruction ahead of the currently executing one, meaning that an instruction is being fetched whilst another is executed.


Input & Output devices


Input devices are what allows interaction with a computer system.

Their data is processed by the software in order for an output device to

provide information back to the user. An example would include a keyboard,

mouse or controller.


Optical character recognition -  

Allows printed documents to be converted into a digital text document by a scanner, where it can then be edited. It can be useful for keeping copy of text safe, such as an old book that can then be converted into an e-book. It works by scanning the document for recognisable shapes, such as letters and numbers and the comparing this against a database of known shapes. If no match is found, then that character is skipped, meaning the final produced document must be proof read for errors.



Optical mark recognition –

This works through a multiple choice method, with specific areas being marked for the choice. For example, in a test with options a, b or c, if a is to be picked then a straight black line is put through the A. Then, a scanner detects where a mark is placed on the page and compares it to the correct answer to provide an output. This is only suitable for things like tests and registers, not any written text.

Magnetic ink character recognition –

This allows for a special type of ink containing iron oxide to be read by a special scanner. Normal ink won’t affect hoe the data is read, as it only detects the one with iron oxide. This is very useful for cheques, as the account number and cheque number can be read extremely fast by the reader, therefore speeding up the process in banks. This also avoids the use of OCR, which can often cause problems with missing data – extremely bad for anything involving money!


Touch screens -

Included in almost all modern handheld devices, touch screens have made navigation through pages and increased usability hugely. There are 2 types of touch screen, resistive and capacitive. The way both work is by having the screen split up into hundreds of tiny areas, each with a unique (x,y) location.


Resistive touch screens are made of 2 thin, transparent sheets and work by recording a voltage when these 2 sheets meet. These screens are usually lower quality, lack multi-touch gestures and are therefore cheaper.


Capacitive screens provide a better image and work by benefiting off the fact that the human body conducts electricity by creating an electric field around the area touched each time. The device can recognise this change in voltage and therefore register it as a touch and return the (x, y) position. Despite lacking the ability to work when hands are covered up, these screens allow for multi-touch and provide better quality so therefore are more expensive.


Dictation systems


Voice inputs

A normal voice input uses the built in microphone of a device and attempts to interpret speech as instructions and process them.


In Vocabulary diction, the device uses the microphone to turn speech into text. This can be useful for sending messages, as this is the natural way to communicate. In Voice-print recognition, a person’s voice-print is captured and stored. This can be used in security, with the captured voice being compared against one already stored in the system. This is what enables only the owner of an iPhone to say ‘Hey Siri’ and cause Siri to be activated.


Using vocabulary diction over a keyboard reduces the risk of RSI, increases speeds, reduces the hardware needed and helps people with a disability. However, it can often cause mistakes, be interfere with background noise, prevent users who have trouble speaking using the device and many words have similar sounds.


Secondary Storage

Storage devices store user applications, user documents & files and the operating system


Magnetic Storage

This is a hard drive, meaning that there is a fairly fast access time and read/write speeds. However, in comparison to other storages they lack speed, but make up for this with their relatively low price. Overall, this creates a good compromise between performance and costs. Hard drives are commonly used in cheaper computers, laptops and for security footage, where storage is the most important thing.

Data is stored on a hard drive platter and is read via a read/write head on the end of an arm. The platter is split up into sectors and as the disk is spun, the arm travels across the disk. The head and movement of the disk work together to enable every sector of the disk to be reached. Data is encoded using special binary technique and stored on a small magnetic flux on the disk.

The speed of these disks is measured in RPM (revolutions per minute) and a common speed is 7200 RPM. The faster the platter spins, the faster the data can be read, therefore hard drives with a higher RPM tend to be more expensive.

Flash storage

Examples include memory sticks and Sd cards, but the most common is an SSD (solid state drive) that can replace a hard drive. They have faster read/write speeds and are able to retain their state once power has been switched off. This means they are great for transporting files, hence the memory sticks commonly used today.

Optical drives

These are used to store media, or programs and often come as either CD's or DVD's. This is due to their extremely low cost and suitable capacity for this kind of information.

They work by using lasers to burn microscopic indentations into a disc when writing data. The indentations are created in a spiral pattern, outward from the middle. This creates pits and lands and this is how data is read. A laser is aimed at the disc and is reflected back, causing interference with the other laser. The change in interference is how the drive detects pits and lands.

Blu-ray uses the same technique, but with a smaller wavelength and blue laser. This allows for pits and lands to be closer together, creating more storage space for higher quality data. When created, the disc cannot be modified and so they are often used for a backup of data.


Files aren't always stored in one place. they are stored in 'clusters' and the device must collect the data from each related cluster in order to retrieve the whole information. This is called fragmentation, as the data is split over the disc. The more fragmented the disc, the longer the disc heads have to move between different parts, therefore increasing the time needed to fetch the data.

Defragmentation involves re-arranging the clusters on a disc  so that the different sections are closer together, reducing the loading process time.

However, this is only useful for magnetic hard drives and not SSD. This is because the SSD already uses direct access, knowing the exact location of each cluster. This means that there would be no improvement in speed times, due to the lack of a physical head and defragmentation may even reduce the limited lifespan of an SSD.

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