4. Hardware Devices Flashcards
How does a digital camera work
- Light is focused in lens onto image sensor
- Image sensor is an array of RGB photo sensors - Bayer filter
- Individual colour arrays combined to form image
- RGB values captured, stored digitally to flash memory card
Define Mouse
Enable the user to exectueicommands or instructions to computer by controlling an onscreen pointer
Define keyboard
Alphabetical and numerical keys that complete a circuit when pressed down. This transmits a binary signal, usually in ASCII of the key pressed
Define voice recognition
Microphone connected to software that converts human speech into commands or text.
Often struggles with similar words, and accents
Explain how a barcode reader works
- Laser is directed at the barcode, scanning across it.
- The reflected light is captured by the reader
- High light intensity means it is a white bar, low light intensity means black bar.
- The pattern is translated into binary code to give the identity of the item
- The code is checked against a database. Data information is displayed
Define Optical Code Reader
Black marks filled in to represent answers (often used in multiple choice tests).
Fed into a machine that uses the location of the black dots to determine the answer.
This allows lots of tests to be marked quickly
Define Optical Character Reader
Used in scanning written text ps or books. Scans the contents of page and translates the image into the text it represents
Define Magnetic Strip Reader
Used to read data from bank cards
data is stored in binary on black magnetic strips on the back of the card
Devein Smart Card Reader
Used as the ‘Chip and Pin’ in bank cards.
Data is stored on an integrated circuit
Define RFID
Radio Frequency Identification
Explain how an RFID reader works
- RFID chip with antenna is stored inside a card
- A card is placed above a reader, which produces a magnetic field to create a current in the card (no contact needed).
- Current powers a small transistor that sends data out as a radio signal.
- Data is received and read by the reader
Explain how a Touch Sensitive Screen works
- Each corner of the screen emits a uniform electric field over the screen
- Placing a finger on the screen disrupts the field and draws current
- Measuring the current in each corner allows the location of the touch to be triangulated by the computer
Define Graphics Tablet
Used for design and architecture
Draw on the tablet using a stylus. Pressing the stylus on the screen operates a micro switch which allows the movement it be recorded by the computer. The board contains electronics to determine the location
Explain how a Flatbed Scanner works
- Place an object face down on the glass pane
- Under the glass, light moves along from the start of the document, illuminating a slice
- The slice is reflected onto the CCD ( image sensor array) where the image is stored as digital data
- The light and mirror move onto next slice, repeating the process
- Document is combined to create a digital image
Define Flatbed Scanner
Used to convert images and text into a digital format
Explain how a finger print scanner works
The ridges and troughs in a finger print are unique.
This is scanned and recoded into a database.
Fingerprints are scanned and compared to this database
Retina Scanner
Records the unique pattern of blood vessels in the back of the eye
Explain how an iris scanner works
Takes a picture of the unique blood vessels and colour in the back of the eye.
This can be changed with the use of contact lenses
Define Check Digit
An additional digest added to a data string to check the string has been sent correctly.
If it has not, it will need to be sent again
Define Input Device
Devices that send data or instructions into a computer
Define output device
Device that computer sends data or instructions to
Explain CRT
Cathode Ray Tubes
3 RGB electron guns fire electrons at phosphor lined screen. This produces a colour image.
Explain Flatscreen LCD
Made up of an array of RGB sub-pixels. The pixels are placed between polarised frills that show or hide the sub-pixel when an electric current is applied. This creates the image
Why is CRT better than LCD
More viewing angles
Doesn’t have to use a specific resolution
Why is LCD better then CRT
Smaller, thinner, uses less power
Screen geometry almost perfect as there is no projection
No flicker
Explain plasma screens
Each pixel is controlled by a mini florescent light. When the control voltage is applied, this releases UV light and becomes plasma.
This hits the phosphor screen to create an image.
Advantage of LCD
Small, light, doesn’t use lots of power, screen geometrically correct.
Define speech output
Words in electronic documents can be output as spoken words using synthesis software through a sound card and speakers
Define Electronic Paper
Creates images using tiny coloured balls that rotate or move in response to an electric charge to change the image.
Describe an Impact Printer
Dot Matrix Printer. Used for anything that requires force, like carbon copies or Multi-Part Stationary.
The ribbon is struck hard by metal pins to create a letter on a vertical line by line basis
Explain An Inject Printer
Non Impact printer, droplets of ink sprayed onto paper to create image
Explain how an Inject Printer works
- Paper fed into printer
- Print head contains cartridges of CMYK (cyan, magenta, yellow, BLACK) ink.
- Print head moves from side to side spraying particles of ink
- Paper is fed through so ink covers whole page
Advantage of Inkjet Printer
Cheaper than lasers, produces high quality images
Define Laser Printer
Non impact printer that rapidly produces high quality text or graphics. Used with vectors
Explain how a Laser Printer works
- Drum is given a negative charge
- The laser erases the charge in the correct place for the image
- Drum covered in negatively charged toner which is repelled by the charge
- Drum is rolled over page, transferring the image
- Paper goes through heated rollers which melt and seal toner onto paper
Advantage of laser printer
Fast, cheap in large volumes
Define Plotter
Non impact , used for vector graphics or text
Explain how a plotter works
- Paper placed in plotter
- Plotter arm selects ink of correct colour
- Arm moves pen to area where plotting begins
- Pen is lowered onto paper and arm moves it, creating a continuous image
- Pen raises and can change ink colour
Define Seek Time
Average time taken from requesting data to data being read
Define Capacity
The amount of data it is possible to save
Define Write type
Whether device is Read-Only, Write-Only or readable and writable
Define Secondary Storage Device cost
How much it costs per megabyte
Define Access type
Random access or serial access
Define Magnetic Media
Assigns a magnetic charge to metal to represent binary 1s and 0s
Define Hard Disk Platter
Magnetised magnetic disks that store data. Spins thousands of times per second.
There may be multiple platters that store data on both sides.
Platter is split into cylindrical tracks, and then sectors
Define Hard Drive Head
Reads magnetic data from platter. May be 2 heads per platter for top and bottom
Define Hard Drive Actuator Arm
Used to move head in and out of the platter as it spins to easily access data
Define Hard Disk Track
Cylindrical concentric rings on the platter
Explain how Hard Disk works
- Platters spin around spindle
- Data is requested on specific track/ sector on platter
- Actuator arm moves head to correct location
- Once the disk has spun around, the data has been read
- Data is sent to main memory
Advantages of Hard Disk
Cheap, stores up to 4 terabytes, readable and writable
Fast Seek time, low cost, high capacity, Random access
Can be physically damaged easily
Explain how Magnetic Tape drive works
Data is stored on a read only section of magnetic tape.
Data is serial and must be read through to locate. Not Random access
Advantages of Magnetic Tape
High capacity, cheap.
But serial data
Define Optical Media
Disk has pitted magnetic surface to represent Binary 1s and 0s.
Pits get closer and smaller for higher capacity devices
Define CD ROM
Read only, 650mb
Define CD-R
Read / write once. 650 MB
Define CD -RW
Re-Writable, 650MB
Define DVD ROM
Read only, 4.7 - 9.4 GB
Define DVD-R
Write once, then read only, 4.7 -9.4 GB
Define DVD -RW
Re-writable, 4.7-9.4 GB
Define Blu-Ray
Re-writable and read only versions available. 25 -128GB.
Uses blue laser with much smaller pits and lands to store mor data
Explain how USB flash drive READS
- Insert USB. USB driver allows computer to read/write to flash drive
- USB folder structure is sent to computer so user can choose files
- USB returns data from chosen location
Explain how USB Flash drive WRITES
- Insert USB. USB driver allows computer to read/write to flash drive
- USB folder structure is sent to computer so user can choose files
- Computer sends data to the USB Flash drive, data placed in empty space.
- USB flash drive sends updated folder structure to computer
Advantages of USB Flash drive
Fast Seek times, cheap.
Limited capacities and expensive per MB compared to Hard Disk Drives
Define Memory Card
Works in the same way as USB flash drives. Often has different connectors and smaller sizes that allow them to be used inside other devices like cameras and phones.
Can be turned into USB Flash drives.
