Input & Output Devices

Data input and output

There are many examples of input devices such as the scanner, keyboard and more - if data is send to the the system from a device this is a considered as an input device.

There are many examples of output devices such as speakers and storage devices - if data is sent out by the processor it is an output device

General and special purpose computers

General purpose computers are computers which are used in day to day life like your laptop

They can be used to do a variety of jobs such as watching videos and games

There are also computers which are the size of chips and are usually installed on large devices such as a car

These are known as embedded systems or special purpose computers which are able to perform a specific job or function

As usual a computer must have a processor and I/O system and a memory unit. Usually this is built in to one chip and is usually called a microcontroller.

Embedded systems are usually installed on devices to connect the devices to the internet and provide more functions

However as the embedded systems doesn't have an Os and only some simple code, it makes it easier to hack them

Main or primary memory

The computer has main memory which is divided to two types of main memory RAM and ROM

RAM

This is called random access memory

They are used to store programs and part of the Os currently in use

Data can be written to or read from many times

They are volatile (data is lost when the power is switched off) and so they store data temporarily

There are two types of RAM:

• DRAM

Dynamic RAM

This type of RAM stores data in capacitors and transistors where they are contantly charged to prevent data leaking out and losing their identity

This usually has a greater capacity than SRAM

They are much cheaper than SRAM but more slower to access

Also DRAM uses less power

DRAM has more memory cells per area than SRAM



• SRAM

Static RAM

Data are stored in flip flops

Has a very fast access time and thus used for cache memory

Stores less data than DRAM and is more expensive and uses more power than DRAM




ROM

Read only memory

Data can only be read from many times but can not be written

It stores boot up instructions such as the BIOS

It is non volatile memory and so it is permanent

Usually ROM chips contains the instructions when the chips are manufactured but the other 3 are slightly different

There are three type of ROM:



• PROM

Programmable ROM

The chips are given to the people who installed the code. Once installed it can not be changed and must be replaced



• EPROM

Erasable PROM

This are ROM chips which data can be erased in the presence of UV light, however the chip must be removed from the circuit board



• EEPROM

Electronically erasable PROM

Data in the ROM can be removed using an electric signal and data can be written to it, but this is done very rarely




Buffers

A place made in the memory where data is temporarily stored when moving data from one location to another which functions as a queue

When data is transmitted at a faster rate than it is processed or displayed ( Bit streaming ) then data must be temporarily stored as a queue

Secondary memory

There are many types of secondary memory, we will discuss them




Magnetic strips and magnetic cards

These store data on magnetic strips as there are varying magnetic field dots across the strip.

Depending on the magnetic field the dots can either store 1 or 0

So usually a read head is used to read the data and due to the varying magnetic fields it induces and a varying current




Hard disk

This also uses magnetism to store data

Data is stored in many disks called platters which are spun at high speeds

The disc are usually made out of aluminium plated with glass

There is a read-write head on each side of the platter which either reads or writes data using the magnetic properties - this done by varying the electric current in the write head

Data is stored in concentric tracks(circle) in each platter

The tracks are divided into sectors and the sector contains the smallest unit of storage.

Data in the hard disk are stored in blocks

There is a confusion between a disk sector and a track sector

When we talk about sectors, we are talking about the track sector which is a sector a single track and not the whole disk




The above points are enought to score full marks

For more information - similar data are stored on different disc of the same sectors

Data are stored in sequence on the concentric tracks




Optical media

This uses a way different property and this is used by CDs and DVDs and more

The CD - ROM and DVD - ROM have slightly different mechanisms which we will discuss



• CD - ROM

Uses a red laser light to read data

This is done by the read/head

The disc spins at high speeds

This stores data in spiral tracks

The surface contains pits and lands

The red laser is reflected by the surface. The pits reflect less light than the lands - this is then decoded in to binary code



• DVD - ROM

Data is stored in concentric tracks so data can be read or written simultaneously

Uses red laser however the wavelength is slighlty smaller

DVD - ROM contains two discs so it can store more data

The data is read using read heads

The disc is also spin at high speeds

This also stores data in pits and lands



• CD - RW

A disc which is rewritable means that data can be burned/recorded and also erased

The surface of the disc contains a special alloy

When the red laser in focused on to the surface the alloy it forms a liquid which either cools down to a crystalline solid or a amorphous solid depending on the intensity of the laser.

The crystalline solid reflects more light than the amorphous solid.

This can be decode into binary data

This process of storing data is usually known as burning



• Blu-ray

This uses a blue laser light which has a shorter wavelength

This means the light can be more focused and so the pits and lands are closely together and so higher storage




Solid state media

This is the technology used by flash sticks and pen drives

This stores data in transistors called memory cells

This controls the movement of the electrons through the ciruits using either NAND or NOT gates

NAND Gate is used most frequently than NOT whereas NOT gates are very expensive

Also data in the memory cells could be all deleted and written at once




The solid state drive which is used instead of the hard disk uses the same solid state technology and there are many advantages over the Hard disk drive

1. The main advantage of using SSD over HDD is that SSD has a faster access time so it is usually fast

2. Also SSD does not have any moving parts and so it is more reliable and more long lasting

3. Also SSD is more lightweight and portable as no moving parts, also it uses less power




We will need to know some advantages of HDD over SSD

1. The main advantage of HDD is that it usually has a higher capacity than SSD

2. Also HDD is very durable under heavy use and thus used in gaming

3. Cheaper than SSD

Summary

Registers and cache memory has the smallest storage and they are highly expensive but has a very fast access time

Secondary storage has a high storage and are cheap but has a slow access time

Screen Displays

There are 3 main types of displays



• CRT

This controls the direction of the electron to display images on the screen

The screen is coated with a substance which when an electron collides with it a light is produced

Each dot on the screen is made when electrons collide with the fluorescent screen and glows

The screen is full of dots which produces an image

This is the old technology of screens and it is not used now



• LCD/LED Screens

The screens is made out of pixels however each pixel is divided into sub pixels which have the color red green blue and sometimes yellow

The Liquid crystal display is able to change the structure in order to polarise light differently by passing a voltage through it

Usually the backlighting is from LED bulbs that is why the newer versions are called LED Tvs.

The older technology is uses CCFL bulbs as backlightings and they were called LCD screens

The white light is able to change color as it passes through the LCD display and so this is done by controlling the voltage passed in each pixel

Finally there is a polariser(filter) which makes the image more clearer and crisp



• OLED

Organic LED

This does not require any backlighting and so the screens are very thin

The screen contains and anode which emits there own light which causes an image on the screen

These are made from polymers which are very flexible

OLED screens are very expensive




Virtual Reality Headset

This contain both input and output components

The displays and speakers in the VR headset are output devices which provide the user with 3D graphics created by the CAD software

The sensors in the VR Headset are input devices which feed data about your position and all

Printers

There are two main types of printers which we will discuss



• Inkjet printers

These spray ink using small printer nozzles - this is done by either using thermal bubble technology or the piezoelectric technology

The ink is sprayed line by line until the whole document is printed

Usually inkjet printers are cheaper than laser however the ink costs more

Also inkjet printers are relatively smaller than laser printers



• Laser printer

This uses the idea of charge and printer toner to produce hard copies

We will need to know each step in the right order

1. Data is sent to the the printer driver to convert it to a form the printer understands

2. Data is stored in the buffer

3. Firstly the drum is given a charge and it starts rotating

4. A red light is switched on and off on the drum as it rotates - when it switches on it discharges the charge on the drum

5. The drum rotates step by step until a full electrostatic image is formed - the discharged areas are the content to be printed

6. The printer toner which is also given a charge sticks to the discharged areas of the drum

7. A charged paper is fed in and the toner sticks to the paper then the paper is passed through heaters which fuses the toner to the paper

8. If you need to print color the paper must go through the printer several times for each color (CMYK)




The advantage of laser printer is that it is very fast and also has a high quality

However, every large and expensive compare to the inkjet printers

The printing cost on the other hand is cheaper than inkjet




Printing Colour schemes

Usually images are displayed using the RGB format, however in t printed documents color is printed using the CMYK format

C - CYAN . M - MAGENTA . Y - YELLOW . K - BLACK

So different levels of cyan, magenta and yellow are used to produce color documents

So to print a colored document it must go for each type of main color




3D Printers

These are used to create 3D objects which are created from of software called the CAD or the CAM(computer aided manufacture)

The printer contain nozzles which sprays the powder or the material and nozzles to spray the glue

The design of the 3D object is made from many layer designs and so the onject is created by layer by layer until the full object is made

After this the object must be finished or cured - final touches




Keyboard

This is an input device

We will need to know the mechanism of this

The keyboard contains wires which are aligned horizontally and vertically. Every key on the keyboard has its own key matrix which when clicked can be uniquely identified

When a key is pressed this causes the wires to be pushed and cause the wires to contact with each other

When the wires contact together it completes a circuit and the signal is sent to the microprocessor

The processor determines the position of the contact and sents a signal to the keyboard ROM and accesses the corresponding character code and then send it to the computers processor

Remember this processing is done by the keyboard itself

The ROM contains the character codes whereas the microprocessor identifies the position of the contact

Touchscreen

This is a bit confusing but touchscreens are input devices this is because we usually talk about the input mechanism and not the display

There are two main types of touchscreens but we will discuss the other ones too:



• Resistive

Touchscree made out of two conducting layers where when touched causes the top flexible layer to contact with the lower layer and so it completes a circuit

So once the circuit is complete the microprocessor detects the position or coordinates of the touch

This is then decode to binary

The main problem with this technology is that it doesn't support multitouch and also the screens have to be pressed quite hard

However, this technology works with gloves and doesn't require hands

It is also the cheapest type to manufacture



• Capacitive

Touchscreen in which when the screen is touched it undergoes a capactive or electric change and this is then detected

Moreover, the screen layer conducts electricity and so can change its electric state

When we touch the screen the electric charge is flowed from the screen to the finger and so there is an electric change and this is detected by the sensors on the corners of the screen

Then the position of the touch is calculated and decoded into binary data




The good feature of this technology is that it can support multitouch if the screen is made out of an array of capacitors, which means the screen is divided in to cells which can undergo its own electric change

The main problem of this technology is that it can not be used with gloves and it requires a finger or a capacitive pen

Also the technology is relatively expensive to manufacture

Other technologies

Other screen technologies include infrared and sound waves

When a finger is pressed the infrared signals or sound waves are blocked or weakened and detected by the sensors

The position of the touch is calculated and decode to data by the processors




Scanners

In order to convert a hardcopy to a softcopy we need scanners

Usually the paper or the document is fed in and a bright white light is shined over this document

The reflected light from the document is focused using lenses and mirrors to a light sensitive screen known as the CCD - charge couple device

The CCD contains smalls photoelectric sensors which converts the light into electric signal. Also the electric signal produced is proportional to the intensity of the light

Each cell or sensor of the CCD represents a pixel when converting and storing the image as BMP or JPEG file

Also the electric signals from the sensors must be converted to digital(binary data) using an ADC convertor

Each cell or sensor of the CCD represents a pixel when converting and storing the image as BMP or JPEG file

Microphones and Speakers

The reason why I combined this is because they are basically the reversed process



• Microphone

This is an input device

You will need to know the components in a microphone

1. Diaphragm

2. Coil

3. Magnet

When the sound is entered due to vibrations in the air, it causes the diagraphm to vibrate and so the coil vibrates inside a magnet

This induces an alternating current which is then converted to digital data using an ADC convertor



• Speakers

This is an output device

You will need to know the components in a speaker

1. Diaphragm

2. Coil

3. Magnet

They have the same components however most of the time they have extra components such as a filter and a amplifier

This is basically the reversed process. Data or signals sent from the computer must be converted to analogue data using DAC convertor and so then the varying electric signals causes the coil and the digraphm to vibrate and cause sound

Rarely asked devices

We will discuss some rarely asked devices




Graphic plotter

This device is an output device which is used to display the vector graphics on to a paper

This uses a pen which can move to draw the vector graphics and also the paper can move. This produces high quality vector graphics on to paper




3D scanners

This is an input device

This uses the principle of tomography where the objects is broken down to small layers and stored in the computer

Usually the layers can be viewed using the CAD software

This technology is used in MRIs




2D and 3D cutters

This is an output device

This uses either laser or high pressure water to cut objects and the information is given by the computer




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