Comp2 - Hardware devices Flashcards
What does a optical character reader do, and whats it used for?
opical character readers (OCR)- a image of the letters goes in and gets analysed to determine letters.
Used in postal services to get the post code off letters quickly.
What does a optical mark read do, and whats it used for?
A optical mark reader optically senses marks places in predefined positions on a form, registation marks at the edge identify the rows. (sensed based on reflections)
Used in multiple choice, lottery tickets.
What does a magnetic strip reader do, and whats it used for?
Reads info encoded magnetically in a stripe on the back of a plastic/cardboard card based on the orientation of the magnetic particles.
used in credit/debit cards, library cards etc (being replaced by smart cards)
What does a smart card do, and whats it used for?
A plasic card the size of a credit card that holds a integrated circuit chip, which contains a microprocessor,ROM, and busses. (power comes from the reader.)
Used in credit/debit cards, oyster cards.
What does a RFDI reader do, and whats it used for?
(need to know this ones operation) uses radio frequencies to transmit data between a reader and RFDI device without physical elecric contact.
used in oyster cards, short journey tickets,animal tracking, security cards.
1 bit capacity transponders are used in security tags to check its been payed for.
What does a cathode-ray tube do, and whats it used for?
A vacume tube, with a screen coated with phosphor which emits light when struck by e- shot by an electron gun.
used in visual diplays.(not much anymore)
What does a plotter do, and whats it used for?
IT is a kind of “printer” that moves a pen across paper to create a 2d drawing. Drum plotters uses very large pieces of paper.
used to produce large scale engineering drawings.
What does magnetic tape do, and whats it used for?
A cheap way of storing large quantities of data in early computers.
How does a Touch sensitive screen work?(principles of operation)
- Type of VDU that allows interaction
- Either by the breaking of infrared beams.(i think this is bs)
- Resistive screens have , two layers; glass, and a resistive conductive metalic layer. With spacers seperating them, and electricty between the layers. when pressed the layers touch. where it was pressed then gets calculated.
- capacitive screens , the top layer stores charge, which gets lost when touched. circuits that detect charge are in the corners, which by comparisson u can find contact point.
How does a Flatbed scanner work?(principles of operation)
- .Place document on glass pane, with a light beneath it.
- cover to exclude ambient light.
- the light(3 coloured LEDS) shines on the document and different light levels pass through(or reflects)
- this light hits a slowly moving CCD scanner head via reflecting off the document.
- more light reflected from light areas.
- the RGB lights make it possible to scan colour 1 CCD array per colour.
- the light that hits the CCD is converted into a electrical signal, more light= more e-.
- then a digitised image of the whole scan is processed and stored.
How does a digital still camera work?(principles of operation)
- Aputure opens when you press the button and lets in light.
- Lens bends this light onto the light detector.
- Use a CCD or CMOS sensors to sense light intensities across the focal pane.
- The picture is split into dots/pixel
- Each pixel is given a binary code (which says what colour/brightness it is)
- Then stored as a bitmap file containing the list of pixels and their colour.
How does a bar code reader work?(principles of operation)
- Contains a illumination system, decode, and a sensor.
- Illuminator shines red light onto the bar code.
- Light gets refected differently depending on the bars.(more from white)
- Photoelectric CCD sensors detect this light level,and converts it to an analog electrical form of varying voltages.
- The convert turns this to digtal(binary),
- The decoder validates it and turns it to ASCII.
- The 13 digits contain a check digit. This is made when a function is applied to the other 12 digits.
- Check digit used to make sure the code has been inputted manually or scanner correctly.
How does a RFDI reader work? (principles of operation)
- Uses radio frequencies to transmit data between a reader and RFDI device.
- The Item has a transponder.
- When the item is placed near the reader a magnetic field in the reader creates a current in the RFDI circuits without them touching.
- This current powers a radio transmitter in the item which sends its stored data to the reader.
How does a LCD screen work?(principles of operation)
- The LCD screen cotains a backlight, this gets projected through the display to create a image.
- LCD screens are made of pixels, each containing 3-sub pixels (RBG) which allows for coloured light by their varying intensites.
- Behind each subpixel 2 polarising filters at 90 deg to each other, so as default no light goes through.
- Inbetween these filters is a liquid crystal, which when a voltage is applied is switched on and rotats the polarisation of light 90 deg. This means it can pass through the next filter and light can be seen.
- The crysals are turned the correct amout for the colour and brigntess needed.
How does a impact printer work?(principles of operation)
- They make physical contact with the printing surface.
- Use a inked ribbon above the card etc so ink is transfered as well as a inprint.
- A metal 24 pin head is then stamped onto this ink ribbon and card.
- The pins change for the letter they are making to for that character outline.
- This can be done through multiple sheets , eg in enverlopes to mark the letter and carbonised envelope , or for multiple copies.
How does a inkject printer work?(principles of operation)
- Recieves print data, store in buffer, does a clean cycle.
- Steeper motor activatices and checks for paper to feed.
- Steeper motor move the print head across the picture stopping when the ink is sprayed.
- Some use thermal bubbles to transfer ink.
- Ink gets heated behind the nozzel, and a buble extends out the nozzle and pops on paper. Contains hundreds of nozels.
- Some use piezoelectric crystals. These are in the ink wells, and they charge the ink and cause it to vibrate out the nozzel.
- uses Cyan, magentam yellow and Black (k) inks which combine(subtractive mixing) to make all the colours. (one colour at a time )
- Printed a line at a time.
- ink dries before being ejected
- Print head gets parked at the end, and the paper is rolled out.
How does a laser printer work?(principles of operation)
- Prints a whole page at once.
- Page being printed is described as lines, polygons and arcs, and generates a bitmap of this in raster memory.
- A negative charge is applied to the whole photosensitive drum.
- lasers directed at the drum via mirrors turn on and off which cause the -ve charge to neutralise of become +ve, acording to the bitmap being printed.
- The charged surface is exposed to a toner which has -ve charge. which attached more to +ve areas. Higher voltage diff between toner and drum =darker.
- Roll and press the drum onto a peice of paper to transfer the toner(sometime +ve back panel to help).
- paper gets passed through heated rollers to fuse the toner.
How does a hard disk work?(principles of operation)
- A HDD consists of one or more discs/platters coated with magnetic material
- these spin at upwards of 5000rpm .
- Read/write heads can move out over the disc surface to read or change the magnetic properties of the surface to represent 1s and 0s of data being read or stored.
- The disk surfaces are organised into regions of concentric rings, or tracks,which are split into ‘pie wedges’ or sectors .
- The combination of track and sector defines the data storage area to be read or written to as the disk revolves under the head. Whole sector gets read at once.
- The Print head is parked not over the disk.
How does a USB flash drive work?(principles of operation)
- A USB flash drive is a NAND-type flash memory device pluse USB interface.
- most use type-A USB connection, while allows direct connection to a pc/port.
- NAND type means you can rewite certain parts.(NOR is certain bits)
How are CD-ROM,CD-R and CD-RW different in their operation?
All contain a very long sipral track of data, reflective areas=1 and non reflective =0. 200-500 rotations/min
- CD-ROM-Compact disk read only memory. Used in software distribution.
- Data is written on disks using disk mastering pits that physicall add pits to the spiral tracks of the cd, on the reflective metal layer.
- Read by focusing a laser on the refective layer thats been pimpressed.
- CD-R
- Can be written only once, but read many times.
- (Bits are recored by burning a pit in a thin film of metal using a high power laser. OLD)
- The recording beam creates a spot of less reflective disc, reacting the reflective gold layer with its dye coating by heating it with a more powerful write laser.which changes the dyes transparency.
- read by lower power laser.
- CD-RW - can be read and written many times.
- CD-RW drivers have a magnet and a laser. both are used to write only laser used to read.
- To change data, the laser heats a precise spot on the disk to 200degrees, the magnet is then used to set the state of the data bit. (pahase change material changes state.amourphos-crystalline states which reflect differently)
- The laser light is bolarised by reflecting off the disk, the degree of this indicates the value of the data bit.
How much data can a CD_ ROM, CD-R and CD-RW store?
600-700MB
how much data can a magnetic hard disk store?
19.3GB-1.2TB (bs i have a 2TB)
how much data can a magnectic floppy disk store?
750KB-1.5MB
how much data can a magnetic tape cartridge/cassettestore?
10-800GB
how much data can a DVD-ROM,DVD-R,DVD+-RW,DVD-RAM store?
2.8-17.1GB
how much data can a blu-ray store?
25-50GB(higher now)
how much data can a PDD store?
25-50Gb
how much data can a HD DVD store?
15-51GB
how much data can a USB flash drive store?
35MB - 128GB
how much data can a memory card store?
128MB - 64GB
