9: External Hardware Devices & Memory Storage

Question 1

explain how a laser printer works

Answer 1

• print drum is coated in charge
• printer generates bitmap of page from the data
• laser beams directed at print drum
• by a rotating octagonal mirror
• laser removes electric charge on drum where image should be dark
• toner is given positive charge
• charged drum picks up toner
• toner is transfered from the drum to the paper
• toner is fused to the paper by heated rollers and pressure

Question 2

give two advantages and disadvantages of laser printers

Answer 2

advantages=

• cheaper in the long run due to toner and cartidges lasting longer
• faster to print
• reliable
• no wet pages

disadvantages=

• higher inital costs
• expensive to repair
• lower quality than inkjet
• higher power consumption

Question 3

explain how barcode readers work

Answer 3

• they consist of a laser light source, lens, photodiodes and a mirror
• the mirror detects light from the laser and directs it onto a printed barcode
• the light reflected by the barcode passes through the lens, focusing it onto the photodiodes
• the photodiodes convert the light into electrical charge
• this charge is measured and processes, forming a digital signal
• the signal represents the contents of the barcode

Question 4

give 2 advantages and disadvantages of barcode readers

Answer 4

advantages=

• affordable
• easy to use
• reliable and accurate

disadvantages=

• limited visibility
• can be damaged by environment
• prone to human error

Question 5

how do barcodes detect errors and explain it

Answer 5

1. check digit calculation - check digit is calculated based on other digits in the barcode. The numerical value of all the digits in the barcode is added up and then a mathematical operation is applied
2. error detection - the scanning device recalculates the check digit and checks if it matches the one read from the barcode
3. error correction - if it does not match then an error is suggested

Question 6

explain how a digital camera works

Answer 6

• light enters and is focused by the lens onto a sensor chip
• each sensor produces an electrical signal
• the signal represents a pixel
• an ADC converts measurement of light intensity into binary data
• colour filter is applied to seperate data values for red, green and blue
• pixels are recorded as an array

Question 7

give 2 advantages and disadvantages of digital cameras

Answer 7

advantages=

• fast
• lots of functions
• can take videos
• pictures can be seen right away

disadvantages=

• need more energy
• more expensive
• digital storage could be lost

Question 8

explain how RFID works

Answer 8

• RFID tag is scanned, the reader emits radio waves which are picked up by the tags antenna
• the power induced in the tags 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
• the wave is picked up by the reader which decodes the information and returns the information to the computer

Question 9

give 2 advantages and disadvantages of RFID

Answer 9

advantages=

• high speed
• multipurpose
• high accuracy

disadvantages=

• high cost
• some materials may create a signal problem
• could fail to read
• hardware can be complex

Question 10

explain how a HDD works

Answer 10

• the core of a HDD consists of one or more metallic platters
• the platters are magnetized with a highly precise pattern of north and south poles. These magentic regions represent the binary data
• positioned above and below each plater are read/write heads. Their primary function is to read and write data on the platters
• an actuator arm is responsible for holding and positioning the read/write heads
• to retrieve the data fom the HDD, the read head hovers just above the spinning platter and reads the magnetic signals

Question 11

how does an SSD work

Answer 11

• consist of NAND flash memory cells and a controller that manages the structure

Question 12

what is the need for secondary storage in a computer

Answer 12

• permanant store of data
• back up data

Question 13

identify three differences between CD-ROM and HDD

Answer 13

• HDD uses magnetic media, CD-ROM uses optical media
• HDD uses magnetic fields, CD-ROM uses pits and lands
• HDD has multiple platters and read/write heads, CD-ROM is single layered