Hardware devices Flashcards
What is access time?
The time from the start of one storage device access to the time when the next access can be started
(time delay between a request to an electronic system, and the access being completed or the requested data returned)
What does access time consist of?
- Latency(getting to the right place on the device and preparing to access it)
- Transfer time
What is the capacity of a magnetic hard disk?
19.3GB - 1.2TB
What is the capacity of a magnetic floppy disk?
around 1000,000 bytes
What is the capacity of magnetic tape cartridge or cassette?
10-800GB
What is the capacity of CD-ROM, CD-R, CD-RW?
600-700MB
What is the capacity of DVD-ROM, DVD-R, DVD-RW, DVD-RAM?
2.8-17.1 GB
Can DVD or CD store more?
DVD
What is the capacity of a blu-ray disc?
25-50GB
Can DVD or blu-ray store more?
blu-ray
What is the capacity of PDD?
25-50GB (same as blu-ray)
What is the capacity of an HD DVD?
15-51GB
What is the capacity of a USB flash drive?
32MB - 5GB
What is the capacity of memory card?
128MB -4GB
What is the access time of a magnetic hard disk?
under 10ms
What is the access time of a magnetic floppy disk?
94ms
What is the access time of magnetic tape cartridge or cassette?
Long
What is the access time of CD?
~100ms
What is the access time of DVD?
~100ms
What is the access time of blu-ray?
110ms
What is the access time of PDD?
100ms
What is the access time of HD DVD?
500ms
What is the access time of USB?
0.8 - 10ms
What is the access time of a memory card?
0.8-10ms
What is a magnetic hard disk used for?
storage of programs and data files
What is a magnetic floppy disk used for?
Backing up and transferring small files
boot disks for operating systems
(type of removable media that contained operating system startup files used to start the operating system if system files on the hard disk became damaged)
What is a CD-ROM used for?
Distributing software
What is a CD-R used for?
transferring files, distributing software, storing photographs, backing up data, archiving data
What is a CD-RW used for?
Backing up data, transferring files
What is a DVD-ROM used for?
distributing software or videos
What is a DVD-R used for?
Transferring files, distributing software or videos, storing photographs, backing up data, archiving data
What is a DVD-RW used for?
Backing up data, transferring files
What is a DVD-RAM used for?
Backing up data
What is a blu-ray used for?
Distributing videos
What is a PDD used for?
backing up and archiving data
What is an HD DVD used for?
Recording high density video
What is a USB flash drive used for?
transferring files, running applications
What is a memory used for?
storing photographs in a digital camera, storing music in audio devices, storing data in mobile phones
What does a mouse do?
Enables the user to execute commands or issue instructions to the computer by controlling a pointer on the screen
What is a keyboard used for?
Entering text into a computer system
What is a graphics tablet used for?
Allowing people to draw in natural way and, with drawing software, to create a digital line drawing
Used in design and architectural industries
What is voice recognition and what is it used for?
A microphone receives input for software which converts human speech into commands or text
Used to give commands to computer and dictate sentences directly into applications
What are the pros of voice recognition?
The natural interface means users can give commands easily without knowing a complex command set
What are the cons of voice recognition?
Sometimes it is not good enough to understand differences between similar words or regional accents
What is a fingerprint scanner and what is it used for?
A security device which scans the ridges and troughs of a finger using light or electrical currents
Used to match prints from a crime to suspects in a database and to allow people into restricted areas and authenticate user logins
What is a retina scanner and what is it used for?
Device which records the unique pattern of blood vessels at the back of a person’s eye
Used to identify people, allow access to restricted areas, authenticate logins etc
What is an Iris scanner used for?
Scans the iris for blood vessels and colouring to be stored as a unique iris code
Difference in irises is sufficient to identify a person
How can people try to avoid being identified by an iris scanner?
Wearing contact lenses
What is an optical mark reader and what is it used for?
Optically senses marks placed in predefined positions on a form
Used for multiple choice forms, national lottery tickets and some customer response forms
How are rows identified in an optical mark reader?
There are registration marks at fixed positions on the edge of the form
What is an optical character reader?
An optical scanner is used to input images of text and the digital images are analysed to recognise characters
scans printed/written text into a digital format
What are two common uses of optical character readers?
used in automated postal sorting to add postcodes in a machine readable format with phosphor dots
Used by amazon and google to scan books
What is a magnetic stripe reader?
Data can be stored in magnetic strips on the back of cards, magnetic particles of different orientations store binary data
The card is swiped slowly and steadily through the reader to induce a current and read data
What are magnetic stripe on cards being replaced with?
smart cards
What are some common uses of magnetic strips?
credit/debit cards, library cards, railway tickets, bus tickets, phone cards, hotel keys, access cards etc
What is a smart card/smart card reader?
smart card = plastic card holding an integrated circuit chip
The reader provides power for the chip when the card is inserted. Applications are stored on the chip and executed by the microprocessor when in the reader
Why can smart cards be used for secure transactions?
They have enough processing power to encrypt and decrypt data
What are smart cards used for?
- credit/debit cards
- railway tickets (eg oyster card)
- electronic cash
What are the pros and cons of smart cards?
- More secure than magnetic stripe cards
- More expensive to make
What does VDU stand for?
visual display unit
What are plasma screens used for?
Mainly large TV sets
How do plasma screens work?
Each pixel is controlled by a mini fluorescent light, when a control voltage is applied the gas becomes plasma, emitting ultraviolet light which hits phosphors at the front to emit visible light
What are the pros of plasma screens?
They have a wide viewing angle
What are the cons of plasma screens?
- Generate a lot of heat which can cause injury
- Generally more expensive than CRT and LCD
- Can have a low contrast
- pixel size is large so screens have to be large to prevent blockiness
- use a lot of power
Why can plasma screens have low contrast?
A low voltage has to be applied to pixels at all times to prevent a very slow response time, pixels always emit some light so contrast is reduced
What is electronic paper?
Screen is made up of very small plastic balls which can be flipped from black side to white side when a current is applied in order to make the pattern of text/picture
What are the pros of electronic paper?
- A current only needs to be applied when image is changed not all the time so less power is used
- Easier to read in sunlight because not backlit
- Long battery life
What is electronic paper used for?
e-book readers (such as the amazon kindle)
some phones
What is speech output?
Words in electronic documents can be output as spoken words using speech synthesis software, a sound card and speakers or headphones
What is a plotter?
Alternative printing technology which used to be common in engineering and architectural firms, good for printing vector graphics
paper is placed in plotter and arms selects a correctly coloured pen, arm moves pen to start of drawing and moves pen across paper in x and y direction to draw
special paper can be used to reduce ink spreading
What is a drum plotter?
Like a normal plotter but the paper is moved not the pen. Perforated edges engage with sprockets and paper rolls back and forwards (paper must be at least 1m wide)
What are the pros of plotters?
- cheap to run
- can produce very precise technical drawings
What are the cons of plotters?
- Hard to combine colours
- slow
- mostly replaces by laser and inkjet
What is magnetic tape?
A ribbon of plastic tape coated in a material which can be magnetised to record bit patterns, can be used to back up software but is mostly no longer in use
Serial access means access times are slow unless continuous sections are dealt with
What are the pros of magnetic tape?
- cheap
- high memory capacity
What is a DVD?
optical media with a pitted metallic surface representing ones and zeros
What does -ROM stand for?
Read only memory
What does -R stand for?
write once then read only
What does -RW stand for?
rewritable
What is DVD-RAM?
A re-writable DVD with built in error control
Are blu-rays re-writable or read only?
re-writable and read only are available
What is blu-ray?
A high density optical disk
A blue laser is used which can recognise smaller pits and lands, meaning they can be more closely packed and more data can be stored (eg high definition video)
What does PDD stand for?
professional disk for data
What is PDD?
Similar to blu-ray but with a lower rate of data transfer, meant for business archiving and back up
What is a memory card?
A non-volatile memory device
What are the pros of memory cards?
-They are easy to re-record on
-Memory is non-volatile so they do not need power to store data
-small
portable and durable
What is volatile memory?
Memory which needs a constant power supply to maintain data
What is non-volatile memory?
Memory which can maintain its stored data without a constant power supply
What is a touch sensitive screen?
A type of visual display unit which lets a user interact with an application
How does a touch sensitive screen work with an electric current?
Each corner emits a uniform electrical field
A finger touching the screen disrupts the field by drawing current, the amount of current drawn from each corner lest the position of the finger be found
co-ordinates are mapped to an action
How does a touch sensitive screen work with infrared light?
The region in front of the screen is criss-crossed with light beams.
A finger breaking the beam is detected by photoelectric sensors at the end of beams and a circuit connected to sensors finds the co-ordinates
co-ordinates are mapped to an action
What are the pros of touch sensitive screens?
- Natural interface with devices
- Screen functions can be remapped to a task (eg bringing up a keyboard for typing)
what are the cons of touch sensitive screens?
- can be affected by cold weather
- screen using current will not work with gloves
What do flatbed scanners do?
convert images and text on paper to a digital format
How do flatbed scanners work?
- Image is placed on a glass plate, illuminated from below
- An array of light detecting sensors (colour scanners have an array for each colour) is moved with the light source along the image
- Reflected light is converted to en equivalent current based on its intensity
- Slices of the image are taken one by one then reassembled back into a full digital image
How is ambient light excluded in a flatbed scanner?
With an opaque cover
How do digital still cameras work?
-Light is focused through a lens onto sensors inside the camera
-Sensors are made up of BAYER FILTER and can record values for red, green and blue
-Values from the different colour arrays are combined again to make a single digital image
(RGB values can be stored digitally on a memory card)
What are the pros of digital still cameras?
- Images can be previewed without development
- Filters can be used for special effects
What are the cons of digital still cameras?
some people think traditional film gives better pictures
What is a bar code?
A sequence of white and black bars encoding information such as a product identifier
often printed on packaging
(Usually the information is also printed in human readable format underneath)
How does a bar code reader/scanner work?
Laser light is directed at the barcode and the reflected light is captured by the reader. A high intensity is white and a low intensity is black. The pattern is translated into a unique code (binary string for computer) which is checked against database values to display product details
What are the pros of bar codes and bar code readers?
- Black and white images are cheap to produce
- Quick to read
- Multi-directional scanners can read from different angles
What are the cons of bar codes and bar code readers?
They can only store very limited data
What does RFID stand for?
radio frequency identification
What are RFID systems used for?
Reading data without physical contact
- Used in electronic article surveillance (EAS) in shops to stop items being stolen
- Tickets for short journeys
- contactless security badges
- animal trackers
How do RFID readers work?
A transponder in the chip is powered by a magnetic field from the reader to create a current in its circuitry
The current powers a small radio transmitter to transmit radio waves containing the information on the card
What is a transponder?
A device which recieves a radio signal and automatically transmits a different signal
What are the cons of RFID readers?
- multiple cards together can interfere so none can be read
- cards can be read remotely to steal details
What are the pros of RFID readers?
- They are a fast way to pay for things
- They can be read without physical contact
What are LCD screens used for?
Most television screens and monitors
How do LCD screens work?
- The screen is an array of pixels
- Each pixel has red, green and blue filters and a backlight which shines through
- The colours are between polarised grills controlled by a current. When a current is applied the grills flip, when they are perpendicular, no light can get through
- An image is built up depending on which colours are blocked and where
What are the pros of LCD screens?
- smaller and lighter than equivalent CRT
- More energy efficient then CRT
- Thinner display than CRT
What are the cons of LCD screens?
- If grills get stuck there are dead pixels
- Viewing angles can be smaller than CRT
How do impact printers work?
A forcible impact is used to transfer ink from a ribbon to paper
most use preformed characters but dot matrix printers make up characters with dots made by pins
What are the pros of impact printers?
- Can print multiple sheets of paper at once
- Very cheap to run
What are the cons of impact printers?
- noisy
- low definition
- slow
How do inkjet printers work?
- Four ink cartridges of cyan, magenta, yellow and black are in the print head
- The print head moves across the paper spraying particles of liquid ink using electrostatics
- one line is printed at a time
What are the pros of an inkjet printer?
- cheaper than laser
- can produce high quality images and text
What are the cons of an inkjet printer?
- slower than laser
- relatively expensive per page
- ink can smudge
- special paper is needed for highest resolution
How does a laser printer work?
- whole pages are printed at a time
- A drum inside the printer is given a negative charge
- The charge is removed in the correct places by a laser
- The drum is coated in negatively charged toner particles which stick to the places where charge has been removed
- The drum rolls over paper to transfer the toner
- heated rollers melt the toner to fuse it to the paper
What are the pros of inkjet printers?
- Cheap to produce large volume of printing
- faster than inkjet
What are the cons of inkjet printers?
Hardware is expensive
What is magnetic media (used in hard drives)?
Assigning a magnetic charge to a metal processed by a read head to convert to 1s and 0s
What are the components of a hard drive?
- platter (disk)
- spindle (thing disk spins around)
- read-write head
- stepper motor
- spindle motor
What is a track?
A concentric ring on the platter of a hard disk
What is a sector?
A subdivision of a track on a hard disk platter, holding a fixed number of bits
What is a disk block?
The smallest unit of transfer between a computer and a hard drive disk (a disk sector)
How is data read from a hard disk?
- The platter spins around the spindle
- Data is requested from a specific area
- The actuator arm moves the read head to that TRACK
- Track spins around until the correct sector is reached
- Data is read and sent from the IDE connector to the main memory
What does an IDE connector do?
Allows transfer of data between hard disk platter and main memory
How is data written to a hard disk?
- Data is sent to the hard disk over the IDE connector
- The actuator arm moves the read-write head to the appropriate track
- The platter spins round the spindle until the correct sector is reached
- The write head writes data to the hard disk by assigning a magnetic charge to the metal
Which side of a hard drive latter can be used to store information?
both
What does a block address for a hard drive platter consist of?
- surface address
- track address
- sector address
What are the pros of hard drives?
- increasingly cheap
- fast seek times
- random access
- high capacity
What are the cons of hard drives?
They are very susceptible to physical shocks
Which CD is read only?
ROM
Which CD can be written to using a home computer but only once?
R
Which CD can be read from and written to multiple times?
RW
How does a CD-ROM work?
A single track runs from the centre to the edge, made from pits and lands to represent 1s and 0s. The pits and lands are impressed using a high power laser (not available in home computers)
A low power laser follows the track as disc spins and different reflections from pits and lands represent 1s and 0s
What are the pros of CD-ROM?
- cheap
- can’t be written over
What are the cons of CD-ROM?
- slow seek time
- Data degrades with time
- can’t be written over
How does a CD-R work?
The disc is reflective, with a layer of opaque dye on top.
A high power laser removes dye to make areas more or less reflective, corresponding to pits and lands
The disk spins and a low power laser follows the track from centre to edge, picking up different reflections from pits and lands
What are the pros of CD-R?
- Can be written to using a home computer (but only once)
- cheap
What are the cons of CD-R?
- slow seek time
- can only be written to once, then data cannot be changed
- data degrades with time
How does a CD-RW work?
The disk is reflective, with a phase change metal on top
A laser heats the metal and a magnet is used to set the data bit. How reflective the metal is is changed.
The disk spins and a laser follows the track from the centre to the edge, the light is polarised by different amounts depending on the phase of the metal, corresponding to 1s and 0s
What are the pros of CD-RW?
- cheap
- can be written to with a normal home computer
- data cannot be affected by external magnetic fields once set
- data can be changed after writing
What are the cons of CD-RW?
- slow seek times
- data degrades over time
- some older CD players can’t read CD-RW
What does solid state mean?
No moving parts (eg USB)
How does reading from a USB work?
- drive goes into USB socket
- driver loads, giving the computer code on how to read from the device
- The USB is read for information on file and folder structure in file allocation table
- The user chooses a file and the computer sends wanted address to the USB port
- The USB returns data in the given location
How does writing to a USB work?
- drive goes into USB socket
- driver loads, giving the computer code on how to read from the device
- The USB is read for information on file and folder structure in file allocation table
- The computer sends data to the USB port to be placed into any empty location
- The computer requests a new version of file and folder structure
What are the pros of USB?
- very fast seek time (no waiting for mechanical movement and random access memory)
- Allows read and write
- very portable
What are the cons of USB?
- limited capacity
- expensive per MB compared to hard drives
