7.4 External hardware devices Flashcards
What are barcodes?
Barcodes are printed diagrams that consist of light and dark portions. They contain information which can be read by a computer using a barcode reader. There are 2 types 1D and 2D.
What is the difference between 2D and 1D barcodes?
2D barcodes can contain more information in the same amount of space as a 1D barcode but require more processing in order for the information to be extracted.
How do barcode readers work?
The mirror directs light from the laser onto a printed barcode. The light reflected by the barcode passes through the lens and is incident on the photodiode which turns light into electrical charge. This electrical charge can be measured and processed to form a digital signal representing the content of a barcode. Light portions of a barcode reflect the most light while dark sections absorb incident light. The pattern of light and dark stripes in a barcode corresponds to binary 1s and 0s.
What are the components of a barcode reader?
Barcode readers consist of a laser light source, a lens, photodiodes and a mirror.
Explain the use of error detection in barcodes?
they can use parity bits and check digits built in allowing computers to tell whether a barcode has been read correctly. If it fails to scan correctly the reader can continue to scan until the parity bits or check digits match. Barcode readers can scan 1000s 0f times a second so the time delay caused by rescanning is hardly perceptible to humans.
Explain how digital cameras work?
Digital cameras consist of a lens that focuses light onto a sensor. The path of light between the lens and the sensor is regulated by a shutter. Two sensors commonly used in digital cameras are CMOS (complementary metal oxide semiconductor) and CCD (charge coupled device) which both convert incident light into electrical charge. Charge builds up in cells, each of which represents a pixel in the image. Once the photograph has been taken, the charge of each of the cells is measured and converted to a digital value which is then processed by the camera and stored as a digital image.
what is a bayer filter?
A bayer filter is a special colour filter used in digital cameras that has the same number of green filters as red and blue combined. Using a Bayer filter produces an image that is a closer approximation of what the human eye sees.
Explain the use of additional cells needed for coloured cameras?
In colour cameras, there are multiple cells for each pixel, each of which has a filter that only allows in certain wavelengths of light. This lets the camera build-up a separate image for intensity of each colour of light which can then be combined to form a full colour photograph.
What is a laser printer and what are its components?
A laser printer is an output device that produces images on paper from digital signals. Laser printers consist of a laser light source, a mirror, a drum, a toner roller and fuses
How does a laser printer work?
When a document is printed, the drum is positively charges all over before the user is directed at its surface by the mirror. Areas on which the laser incident are discharged, leaving behind an impression of the page in electrical charge on the drum. The toner roller dispenses negatively charges toner (plastic powder) onto the drum. As opposite charges attract, toner is attached to the positively charged portions of the drum. The toner is then applied to the paper by the drum before the paper is heated by fuses, fixing the toner to the paper. Colour printers apply the same process with four different colours of toner: cyan, yellow, magenta and black (CYMK) to achieve full colour prints.
What does RFID stand for and what is it?
It stands for Radio frequency identification and is a method of transferring information wirelessly between tag and reader.
How do RFID tags work?
Inside the RFID tag is a chip which contains a small amount of memory. The chip is attached to a coil of wire that acts as an antenna.
1. When an RFID tag is scanned, the reader emits radio waves which are picked up by the tags antenna.
2. The power induced in the tag’s antenna from these waved is enough to power the chip which then uses its antenna to emit its own radio wave
3. These radio waves contain the information held on the chip.
4. The wave is picked up by the reader which decodes the information and returns the information to a computer.
What’s the difference between a passive and active RFID tag?
Passive tags induce enough power wirelessly from the reader to operate the chip. Active tags contain a small power supply and can be used from much further away from readers than passive tags which must be held within a few centimetres of their reader.
What does secondary storage do?
It is used to store files and applications
What are the components of a hard disk drive (HDD)?
A number of circular platters which are made from magnetic material. Above hovers an actuating arm on which is a read/write head.
what does the actuating arm of a hard disk drive (HDD) do?
The actuating arm allows the read/write head, which changes the magnetic polarity of parts of the platters to access all portions of each platter.
How does a hard disk drive work?
Data is written in concentric tracks, each of which is further driven into sectors. The platter rotates thousands of time per minute, allowing for good read/write speeds.
What are two ways of increasing the capacity of hard disk drives (HDDs)?
Adding more platters and decreasing the width of tracks.
Why aren’t hard disk drives (HDDs) good for portable usage?
Due to them having many moving parts they are susceptible to damage from movement.
What are the components of a solid state drive (SSD)?
They consist of NAND flash memory cells and a controller that manages the structure of data on the drive.
True or false NAND flash memory is volatile?
True
How does a solid state drive (SSD) work?
Memory cells are formed of floating gate transistors which store information by trapping electrical charge. Data is stored on SSDs in pages which combine to form blocks.
Explain the difference of how the way hard disk drives (HDDs) and solid state drives (SSDs) overwrite data?
SSDs are not capable of overwriting data. Instead an SSDs controller must completely erase the entirety of a page before writing new information to it.
What is the advantage of solid state drives (SSDs) over hard disk drives (HDDs)?
Because they don’t have moving parts they are capable of far higher read and write speeds than HDDs and are suitable for use in portable devices.
What is the key feature of optical disks?
They store information which can be read optically by a laser. Overall the operation can differ based on the type of disk.
How do optical disks work?
Pits are burnt into the disk by a high-power laser which permanently deforms the surface. Optical disks have one continuers track which spirals from the centre of the disk to the outside edge. When a low-power laser beam is passed over the flat surface of an optical disk it reflects back onto a photodiode. When the laser is incident on a pit, the light from the beam is scattered in different locations rather than reflected back at the diode. The resulting pattern of reflections and scatters can be converted into a digital signal of binary 1s and 0s.
How do rewritable optical disks differ from unwritable optical disks?
On rewritable optical disks the surface of a disk is instead covered by a dye. where this is no dye the disk reader’s laser beam is reflected off the surface. where there is dye the laser is absorbed and not reflected at all.
Compare the 3 secondary storage devices?
hard disk drives (HDDs) have a high capacity with alright read/write speeds. They lack in portability, power consumption and latency.
Solid state drives (SSDs) don’t tend to have a high capacity but have very high read/write speeds, very low latency, are very portable and have low power consumption.
Optical disks are rarely used nowadays as they have very low capacity, low read/write speeds, high latency, not too portable and high power consumption.
