7.4 External hardware devices Flashcards
What are barcodes?
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. 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 how digital cameras work?
Consists of a lens that focuses light onto a sensor.
The sensors are usually CMOS or CCD.
They convert incident light into electrical charge.
They consist of cells each of which represents a pixel in the final image.
A shutter than regulates the path of light between the lens and sensor.
Explain what modifications would be needed for a coloured camera?
There are multiple cells for each pixel each of which has a filter that only allows in certain wavelengths of light.
What’s unique about the Bayer filter?
Has the same number of green filters as red and blue combined and allows a camera to produce a closer approximation of what the human eye sees
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?
The drum is positively charged all over. The laser is directed at the drum’s surface by the mirror to discharge parts leaving behind an impression of the page in electrical charge. The toner roller dispenses negatively charged toner onto the drum. Toner is attracted to the positively charged portions of the drum and applied to the paper. The paper is heated by fusers fixing the toner to the paper.
What modification is needed to make a coloured printer?
Four different colours of toner (CYMK).
What does RFID stand for and what is it?
Radio frequency identification and is a method of transferring information wirelessly between tag and reader.
How do RFID tags work?
RFID tags contain a chip with a small amount of memory, coil of wire acting as an antenna, usually passive inducing enough power from the reader.
The reader emits radio waves which the antenna picks up.
The power induced by waves powers passive tag.
The chip uses antenna to emit a radio wave containing the chip’s information. This wave is picked up by the reader which decodes the information.
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.
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.
How can you rewrite data to an ssd?
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. They have just one continuous track which spirals out from the centre of the disk
How do read-only optical disks work?
Data is stored using pits and lands. Pits are burnt into the disk by a high-power laser which permanently deforms the surface. A low power beam is passed over the surface If an optical disk. When the laser is incident o a land the light beam reflects back onto a photodiode. When the laser is incident on a pit the light from the beam is scattered in different directions. The pattern of reflections and scatters can be converted to a digital signal.
How do recordable and rewritable disks work?
A pattern of reflections and scatters is created by a due on the disk’s surface. If there is no dye the laser beam reflected off. If there is due the leaser beam is absorbed. Recordable discs user a dye which is photosensitive it changes from opaque to transparent under a high-power laser.
Rewritable optical disks use a phase change dye that can be converted multiple times between transparent and opaque by temperature changes.
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.
