7.4 External Hardware Devices Flashcards
What are the main two types of barcode ?
1D,2D
What are the characteristics of 2D barcodes ?
- Contain more info in the same amount of space as 1D but require more processing power
What do barcode readers consist of ?
A laser light source, a lens, photodiodes and a mirror
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.
How do barcodes work ?
Light portions of a barcode reflect the most light while dark sections absorb incident light.
Do barcodes have error detection ?
Parity bits and check digits built in
What do Digital Cameras mainly consist of ?
a lens that focuses light onto a sensor which is regulated by a shutter.
What are two common sensors used in digital cameras ?
- CMOS
- CCD
- Convert incident light into electrical charge
How do digital cameras work ?
Charge builds up in cells, each of which represents a pixel in the image.
Once the photograph has been taken, the charge in 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 Bayler filter ?
a special colour filtre that has the same number of green filters as red and blue combined.
What does a laser printer consist of ?
A laser light source, a mirror, a drum, a toner roller and fusers.
How does a laser printer work ?
o The printer’s print engine converts data from a computer into a laser light print command.
o Corona wires within the photoreceptor drum create a static charge which allows it to attract toner onto the surface the photoreceptor drum.
o The printer’s photoreceptor drum initially receives a positive charge across its surface which begins to roll, there can even be up to 4 different drums for the 4 distinct colours of Cyan, Magenta, Yellow & Black.
o The laser then activates and beams against a series of mirrors before hitting the photoreceptor drum and imprinting the print image by negatively charging the surface at specific points.
o Then the toner cartridge located next to the photoreceptor drum releases positively charged toner powder which is attracted to parts of the drum’s surface which are negatively charged.
o As a result, positively charged areas of the drum are left untouched.
o The transfer belt rolls the paper through the printer giving it a positive charge where, as it passes by the drum the negatively charged toner particles are attracted to the page in the shape of print.
o The paper and toner then pass through the fuser unit where they’re melted together to produce a final printed page.
What is RFID ?
A method of transferring information wirelessly between a tag and a reader.
What does a RFID tag consist of ?
A chip which contains a small amount of memory attached to a coil of wire which acts as an antenna.
What can active RFID tags do that passive RFID can’t do ?
Active tags can be used much further away from readers
How does a RFID tag work ?
- When an RFID tag is scanned, the reader emits radio waves which are picked up by the tag’s antenna .
- The power induced in the tag’s antenna from these waves is enough to power the chip .
- Which then uses its antenna to emit its own radio wave , which contains the information held on the chip.
-This wave is picked up by the reader which decodes the information and returns the information to a computer.
What do Hard disk drives consist of ?
circular platters, an actuating arm, read/write head.
How do HDD’s work ?
· The HDD has spinning disk called platters that store data using an electrical charge.
· The actuator arm moves the read/write head across the platter.
· The read/write head then reads or writes data to the platters.
· Each platter is divided into small sections called sectors.
· Each sector is then divided into thousands of subdivisions called bits which store an electrical charge.
· The bits store data as magnetic polarities, with positive polarities representing 1s and negative polarities representing 0s. This magnetic force occurs when electric current travels through a wire making a small electromagnetic effect.
· As a result, the read/write head translates the magnetic polarities into binary code
· However, this also results in a latency before information is retrieved as the arm must move to find the correct location on the disk.
What do SSD’s consist of ?
NAND flash memory cells and a controller
What’s the purpose of a controller in a SSD ?
Manages the structure of data on the drive.
What are the characteristics of NAND flash memory ?
non-volatile
How does NAND flash memory work ?
memory cells formed of floating gate transistors which store information by trapping electrical charge.
How is data stored in SSDs ?
Stored in pages, which are combined to form blocks.
Are SSDs capable fo overwriting data like HDDs ?
No a SSD’s controller must completely erase the entirety of a page before writing new information to it.
