1.3.5 (b): describe the principles of operation of HDD's

A Hard Disk Drive (HDD) is a common secondary storage method, which makes use of magnetic disks to store data.

A typical HDD will have a number of disks (or platters) which can spin around 700 times per second. Usually, each platter has two surfaces to store data.

A number of read-write heads have access to the surface of the platters. Typically, they can move from the centre of a platter to the edge and back again 50 times a second

On the platters, data is stored in sectors and tracks. Each sector has a fixed number of bytes.

Note: no need to learn D

-The real disadvantage of HDD's is latency (latency is the time taken for a block of data on a track to to rotate around onto the write/read head)

- Since many applications require the read-write heads to look for the correct sectors to read/write data, a big number of head movements are required.
(A user will experience this latency when you see a message from program saying "Program not responding")

1.3.5 (a): describe the principles of operation of RAM and ROM

There are two types of RAM: static RAM and dynamic RAM.

RAM and ROM are both primary storage (memory)

RAM = random access memory (RAM)is volatile memory used to store data files or part of an operating system which is currently in use. It can be both read from and written to.

-volatile means it's temporary memory. So the contents of the RAM will be lost, when power to the RAM goes.

-RAM never runds out, but it gets slower through time.
-As RAM becomes full, the processor has to access the Hard-Disk Drive (HDD, also secondary storage) to replace old data on the RAM with new data.
-But by increasing the RAM size, the number of times this access operation is done is reduced, making the computer run faster.

DRAM

Dynamic RAM (DRAM) chips are made up on numerous capacitors and transistors.

Capacitor = Holds a bit of information (0 or 1)

Transistor = Like a switch; it allows the control circuitry on the chip to read from or write to a capacitor

-DRAM needs to be refreshed constantly (capacitors need to be recharged). Every 15 microseconds. If they aren't. The capacitors will lose their charges and their values will 0's

SRAM

Static RAM (SRAM) doesn't need to be refreshed.
-Instead of capacitors and transistors, SRAM makes use of "flip flops" to hold bits of memory.
-SRAM also provides faster access speeds 
>DRAM access speed is normally 60 nanoseconds
>SRAM access speed is normally 25 nanoseconds.

ADVANTAGE OF DRAM
-Less expensive to manufacture
-Consumes less energy
-Has a higher storage capacity

ADVANTAGE OF SRAM
-Doesn't need to be refreshed.
-Data access is faster.

ROM

Read-Only Memory (RAM) is non-volatile memory used to store the start-up instructions for a computer system (e.g BIOS). It can only be read from.
-Data isn't lost when power is turned off.

Application of RAM and ROM

Lets say a toy car has a circuitry which contains a RAM chip, a ROM chip and a SSD.

The ROM chip will store the factory settings and the start up routines

The RAM chip stores the instructions sent from the controller

The SSD will be used to store the instructions to operate the car.

And finally, suitable input device. Like a touch screen as there aren't many buttons

1.3.4 (h): describe the principles of operation of projectors and describe how they are applied to real-life scenarios.

Two types of projectors:
-Digital Light Projectors (DLP)
-Liquid Crystal Display (LCD) projector

DLPs

-DLP's use millions of micro mirrors on a chip. The number of micro mirrors and the way they are arranged determines the resolution of the image projected

-When the micro mirrors are tilted towards the light source, they are 'on'. When they are tilted away from the light source, they are 'off'

-So the micro mirrors switch 'on' or 'off' thousands of times a second to create various shades of grey. The typical number of grey shades which can be produces is 1024.

- For example: If the mirror turns on more times than it turns off, a lighter shade of grey will be produced.

-A bright white light source (from a xenon light, for example) passes through a colour filter on it's way to the DLP chip.

-The light is split into the three primary colours (RGB) 

-The on and off states of the mirrors are linked with the 3 colours to produce the coloured image.

-Over 16 million different colours can be produced.

LCD projectors

1.3.4 (g): describe the principles of operation of monitors and describe how they are applied to real life scenarios

Definition: A screen which displays an image generated by a computer

LCD
-Most monitors and TV's nowadays use Liquid Crystal Displays (LCD) technology.

In LCD's, the front layer of the screen is made up of liquid crystal diodes. These diodes are grouped in threes or fours, (known as pixels!)

The groups if three are: Red, Green and Blue
The groups of four are: Red, Green, Blue and Yellow. (This makes the colours more vivid)

Modern LCD monitors are back-lit using Light-Emitting Diode (LED) technology, which is designed to give the image better contrast and brightness.

Back then, LCD's used Cold-Cathode Fluorescent Lamp (CCDL) technology as the back lighting method.

Whats the difference between the way LCD's light up the screen and CCDL's light up the screen?

CCDL's use two fluorescent tubes behind the LCD screen, while LED's (LED technology) use a matrix of tiny LEDs behind the LCD screen.

Advantages of LEDs over CCFL's:

-LED's reach their max brightness faster than CCFL's do.
-LED's produce a white light, sharpening the image and make the colours look more vivid.
-LED's produce a brighter light, improving colour definition.
-LED's last much longer, making their use more reliable.
LED's are more efficient and use less energy, this mean they produce less heat.
-Monitors that use LED technology are much thinner than those which use CCFL technology.

OLED

We also see advancements in LED technology: we have Organic Light Emitting Diode (OLED) technology.

-These make use of organic materials, made up of carbon compounds, to create flexible semi-conductors.

-Organic films are placed in between two charged electrodes (a metallic cathode and a glass anode)

-When an electric field is applied to the electrodes. They emit light! This means no backlighting is required, allowing for very thin screens.

-OLED is a self contained system, which means that there is no need for LCD technology.

-OLED allows screens to be curved, since they are flexible. This ensures a good picture from any angle.

-Due to its flexibility and thinness, OLED screens can be bent into any shape. If this is applied to mobile phones, you can fold your phone and put it in your pocket or wrap it around your wrist!

Advantages of OLED's over LCD/LED's:

- OLED screens are thinner, lighter and more flexible.
-OLED layers can be made of plastic rather than glass, which means they can be made into large, thin sheets.
-OLED's give a brighter light.
-OLED's have a large field of view (around 170°), making them ideal for TV's and advertising.

1.3.4 (f): describe the principles of operation of speakers and describe how they are applied to real-life scenarios

Definition: A device that converts electrical impulses into sound.

Sound is produced from a computer by transmitting digital values through a DAC and then through an amplifier and finally to the speaker where it is output

-The rate that the DAC can convert the digitial data into analogue voltages is known as the sampling rate. 

-If the DAC is 16-biit, it can accept 2^19 numbers. 
Then the speed that these values can be converted is the sampling rate.

-The typical sample rate is 44,100 Hz (samples per second). This means the DAC can convert 44,100 values every second.

Example:
A CD holds music files
Each music file is sampled at 44,100 times per second, each sample being 16 bits.
We must also take into consideration the music being stereophonic.
Taking the above into account, we can calculate how many bits per second can be sampled to the CD.

44,100 = sample rate
16 = sample amount of bits
2 = stereophonic so theres two sides

44,100 x 16 x 2 = 1,411,200 bits per second

8 bits = 1 byte

1,411,200 / 8 = 176,400 bytes per second

1.3.4 (e): describe the principles of operation of actuators and describe how they are applied to real-life scenarios.

What is an actuator?

An actuator is an electromechanical device used to operate or control something.

(e.g a motor or a valve)

-An actuator is used in controlling applications

-When energised, an actuator can operate or control a system (for example, a solenoid could be used to operate a plunger or control a fuel injection system)

- A digital to analogue (DAC) converter is some time required to control an actuator. A computer (or microprocessor) is connected with the actuator and data sent to it will go through the DAC when being transmitted to the actuator.

1.3.4 (d): describe the principles of operation of 2D and 3D laser cutters and describe how they are applied to real-life scenarios

-A laser cutter can cut materials such as glass, polymer, metal, crystal and wood.

-A 2D laser cutter cuts in the x,y direction, while a 3D laser cutter cuts in the x,y,z direction.
-
-Laser cutters are controlled by computers which allows for complex ideas.

1.3.4 (c): describe the principles of operation of 3D printers and describe how they are applied to real-life s

"A printer makes physical objects from a 3D digital model" (usually used in CAD)(computer aid design)

-One type of manufacturing is "additive manufacturing". The 3D object being built up is made layer-by-layer using powdered resin, powdered metal and ceramic powder or paper.

-Another type is "subtractive manufacturing" 
Here the 3D object being printed if carved out a block of stone until the object is formed.

Types of technology

-One type of technology they use is "direct printing". This uses inkjet technology: a print head moves side-to-side like an inkjet printer, can also move up and down to build up the layers. 
(so imagine a print head where you can give x,y,y coordinates instead of just x,y.)

-Another type of technology 3D printers use is "binder printing". The print head moves like in direct 3D printing, but two substances are sprayed for each layer: dry powder and binder to form the object.

-There are other technologies that use UV light to harden liquid polymers, this increased the diversity of products that can be produced

Algorithm:

Uses of 3D printers:

-Make prosthetic limbs for patients.
-Make items which allow precise reconstructive surgery
-Make light weight objects (e.g plane wings)
-Making sculptures

1.3.4 (b): describe the principles of operation of laser printers and describe how they are applied to real-life scenarios

-Laser printers use dry powdered ink instead of liquid ink to print.

-They also use static electricity to print characters and images.

-Unlike inkjet printers, which print line by line. Laser printers will print the whole page in one go. (A bit like compilers with code)

-This gives them a speed advantage, which is why they are suitable for large print jobs.

-They also don't run out of ink halfway through like other printers do.

Laser printer algorithm:

Advantage of laser printers:

-Laser printers have speed advantage over inkjet printers.
-Therefore, laser printers are good for large, high-quality print jobs. (high volume printing)
-E.g (printing exam papers)
-They have large toner cartridges and large print trays.

1.3.4 (a): describe the principles of operation of inkjet printers and describe how they are applied to real-life scenarios

Components of an inkjet printer:
-A print head consisting of nozzles which spray ink droplets on paper to form characters/images.
-Ink cartridges 
-A stepper motor and belt which moves the print head across the paper
-A paper feed which feeds the printer

Thermal bubble:
-Tiny resistors create heat, making ink vaporise.
-The ink forms a tiny bubble which expands. causing some of the ink to land on the paper from the print head. 
-The bubble collapses and a small vacuum is created, allowing new ink to be drawn into the print head.
-This continues until the print job is complete

Piezoelectric:
-A crystal, located at the back of the ink supply for each nozzle, is given a tiny electric charge, causing it to vibrate.
-The vibration causes ink to land on the paper from the print head. 
-Meanwhile, more ink is drawn in for the next print.

Printer algorithm:

Principles of the ink-jet printer:

Uses of inkjet printers:

-They are best for printing good quality one of photos
-This is because of the small sizes of ink cartridges and paper trays, so there would be no issues.

Primary, Secondary and off-line storage

Primary:
The computer's main memory, which is directly accessible by the CPU and much faster than the secondary storage.

Examples =
Random Access Memory (RAM) - Solid State
(RAM will hold the loaded operating system, plus all running applications and files)
Read Only Memory (ROM) - Solid State

Secondary:
A non-volatile storage that holds data until it's deleted or overwritten. Secondary storage is where programs and data is kept for a long-term basis
(Note: could be referred to as external memory and auxiliary storage.)

Examples=
Hard Disk Drive (HDD) - Magnetic Storage
Solid State Drive (SSD) - Solid State)

Off-line:
Off-line is also non-volatile. Can be easily removed from a computer. Often used to transport data and keep backups for protection (Prevent data loss caused by hard disk head crash)

Examples=
CD, DVD, Blu-ray - Optical storage
USB Flash Drive - Solid state
Removable HDD / SSD

1.3.3 (l): describe how sensors are used in real-life scenarios

This is sort of how you will want to structure your answer in the exam. Another example is a burglar alarm system: 

There are lots of marks to attain here, but you get about 1 mark per point. 1 mark for mentioning ADC (analouge to digital converter), 1 mark for including sensors, 1 mark for comparing. etc ...

A controlling system example would be a street lighting system:

The number of minutes pass before another reading is a sort of confirmation that it could be dark or light. This is to prevent the light turning on and of repeatedly if say a cloud went over the lamp.

(Note this is also a cycle)

Exam Question:

(The valve is the actuator)

(a) Name the two sensors used in this application?

(b)Describe how the sensors and the microprocessor are used to maintain the correct condition in the fish tank

Answers:

a = Heat sensor and gas sensor ( oxygen sensor)

b = The temperature sensor and the O^2 sensor send data to the microprocessor through an analogue to digital converter. This data is checked against stored values. E.g checks the 25° and 20 ppm every 30 seconds. If this data is out of range, the microprocessor will send signals to the heater/oxygen supply through an digital to analogue converter (DAC) to correct the error. After this for example, if the temperature is 30° then the microprocessor will send a message to the heater through (DAC) to tell it to turn of for a while. Wait another 30 seconds and say if the temp is 23° then the microprocessor will tell it to turn on for a bit.

1.3.3 (k): describe how a range of sensors can be used to input data in a computer system.

Sensors are devices which can read/measure physical properties.

Physical data is what is knows as analogue. This means that it is 

constantly changing and doesn't have a discrete value. 

Analogue data requires some way to interpret. For example, a mercury thermometer requires you to look at the height of mercury.

Temperature can therefor have an infinite number of values.

As humans, we can read these values. However, a computer cannot. The data needs to be converted into a digital format.

This is where the sensors come in! This is done by using an Analogue to Digital Converter (ADC). This device converts physical analogue values into discrete digital values.

Analogue data ➝ ADC ➝ Digital data

When computers or microprocessors are used to control devices, it is necessary to use a Digital to Analogue Converter (DAC).

These are used with an actuator, which is a type of electromechanical output device used to control something. (e.g relay, motor or valve)

Actuators may require a DAC to receive an electric current rather than a digital signal

Digital Data ➝ DAC ➝ Analogue data

One needs to know all 9 different sensors: (just some applications and what a sensor is)

1.3.3 (j): describe the principles of operation of interactive white boards and describe how they are applied to real life scenarios

An interactive whiteboard is a device which can display computer images on a whiteboard using a projector.

They allow the user to write or draw on it. But unlike other whiteboards, these can be stored in an electronic form to be used for later.

This can be useful in school or meetings

Advantage: Many people can use them at once, can be used for browsing internet and playing games and drawings can be saved for later use.

Disadvantage: Expensive

1.3.3 (i): describe the principles of operation of touchscreens and describe how they are applied to real life scenarios.

There are 3 major types of touchscreen:

Capacitive - E.g I phone

The bottom surface of the upper of the upper layer and top surface of the bottom layer are coated in perpendicular lines of transparent conductive material (Indium Tin Oxide) forming a grid
The screen behaves like a capacitor, storing electrical energy

Infra-red (heat-sensitive and optical)

Resistive

Two layers are separated by an insulating membrane

When the screen is pressed by a finger, the two conducting layers touch and complete a circuit. The coordinates of where the screen is touched is then calculated by a processor

1.3.3 (f): describe the principles of operation of microphones and describe how they are applied to real life scenarios.

A microphone is a device which can input sound into a device

Microphones can be used for:

 Speech recognition

 Voice recognition

 And enabling disabled people to communicate with computers

When a microphone detects sounds, a diaphragm vibrates producing an electrical signal.

This signal is transmitted to a sound card and is converted into digital data and is then stored in a computer

Voice recognition

The user's voice is detected and then converted into a digital wave pattern.

Software will compare this wave pattern with stored wave patterns to see if they match.

If they match, the person has correctly been identified

Only certain words can be used in this as most systems are limited to only recognise key words / phrases.

This technology is good for security

Speech recognition

This is a bit different to voice recognition. In speech recognition, software will try to recognise the words spoken by the user.

The spoken words / phrases can be displayed, input into a word processor or used in other application

The concept of speech recognition is far more complex than that example.

The software must take into account different dialects and accents when trying to recognise what has been spoken.

E.g the phrases "recognise speech" and "wreck a nice beach" sound similar. If the software breaks these up into phonemes, they will be very similar.

Speech recognition can be used in cars. Commands such as "turn on GPS"

1.3.3 (g): describe the principles of operation of pointing devices and describe how they are applied to real life scenarios.

A pointing device is used to control the movement of a cursor on a computer screen.

Some common mice forms:

 Mechanical ball arrangement.

 Red LED used to detect movement

 Wireless

A laptop has a touch pad which can be used to move the cursor.

1.3.3 (f): describe the principles of operation of keyboards and describe how they are applied to real life scenarios.

A keyboard is connected using a USB or wirelessly with bluetooth.

Each character on a keyboard has an ASCII value. Each key pressed is converted into a digital signal which the computer interprets.

Keyboards are quite slow at inputting data, but most probably the easiest way to input stuff.

1.3.3 (e): describe the principles of operation of digital cameras and describe how they are applied to real life scenarios.

A digital camera is a camera which can produce digital images that can be stored in a computer

Back in the day, cameras used film to record photos. The photographer wasn't able to see what they have taken a picture of before it was developed. This made their use quite expensive, as unwanted photos couldn't be deleted.

Now digital cameras have taken over. People can now transfer their photos to their devices using a USB cable or Bluetooth.

A digital camera is controlled by a microprocessor which can:

Automatically focus on images.

Automatically operate the flash

Adjust shutter speed

Adjust the aperture size

Adjust the size of the image

Remove "red eye"

A photograph is captured when light passes through the lens onto a light-sensitive cell.

This cell is made of pixels. The number of determines the file size used to store the image. But by reducing the resolution, the storage requirement is reduced.

The quality of a photograph depends of factors such as lighting and type of lens used.

1.3.3 (d): describe the principles of operation of QR code scanners and describe how they are applied to real life scenarios.

A quick response (QR) code is made of a matrix of black squares on a white background.

Normal barcodes can hold up to 30 digits. QR codes can hold up to 7000 digits, giving a greater scope of storage.

QR codes can be scanned using an app on your smartphone or tablet. Sometimes companies advertise their content by displaying barcodes in public for people to scan.

Advantage of QR code include:

Users don't need to type a URL, they only need to scan a QR code with an app then they're directed to the website

QR codes can be displayed in trains, buses, magazines and business cards. Making them an effective form of advertising

1.3.3 (c): descibe the principles of operation of barcode scanners and describe how they are applied to real life scenarios.

A bar code is a series of black and white parallel lines of different thicknesses.

The numbers 0-9 are represented by the series and thicknesses of the black lines. 

Barcodes usually have a left-hand side and right-hand side, separated by guard bars

Each digit is made up of two black lines and two white lines of different thicknesses

The width of each digit is the same, so the speed of scanning is always the same.

The digits on the left hand side start with a white bar and the digits on the right-hand side start with a black bar, which allows it to be scanned in any direction.

The barcode is read by a red laser (LED)

When this happens, the white bars reflect most of the light while the black bars absorb most of the light, allowing the barcode to be read. This reflected light is read by photoelectric cells.

A pattern is then generated and is converted to digital data.

For example,

A barcode digit may be represented as BWBBWBWB physically but as 10110101 digitally.

(B=black W-white)