External Hardware

What is the barcode made up of ?

Black and white stripes

What is the barcode reader consist of ?

Laser light source
Lens
Mirrors
Sensors

How does a barcode reader work ?

Light shone at barcode
Light is reflected only the white bits
Sensors detect intensity of the light reflected
Charge is measured and processed into a digital signal representing the barcode

How does the barcode use error detection ?

Parity bits and check bits to allow the computer to tell if barcode has been read correctly

Where are barcodes used ?

Supermarkets
E tickets

What does RFID stand for ?

Radio Frequency IDentification

What does an RFID consist of ?

Chip which contains small amount of memory
Antenna

What is a passive RFID ?

Uses an antenna to pick up electromagnetic power when in range of a reader

What is an active RFID ?

Has a small battery to power it

How does an RFID work ?

Tag is scanned and the reader emits a radio wave which are picked up by the antenna
Power is induces the tag antenna
Tag uses antenna to emit its own audio waves containing information on the chip
Reader picks up the radio wave and decodes it

What does a digital camera consist of ?

Lens that focus light onto a sensor and the path between the lens and sensor is regulated by the shutter

What does CMOS stand for ?

complementary metal-oxide semiconductor

What does CCD stand for ?

charge coupled device

What does the CCD and the CMOS do ?

Sensors that record the amount of light received and converts it into digital values

How does a digital camera work ?

When light hits sensors build up in cells
Once photo is taken it the charge of each cell is measured and converted into digital values
They are processed and stored

How does a colour camera work ?

Multiple cells for each pixel with a filter that only allows certain wavelengths
Camera build up separate image for each colour and then combines them

What does a laser printer consist of ?

Laser light
Mirror
Drum
Toner
Fusers

How does a laser printer work ?

Drum is positively charged before laser is directed at its surface by the mirror
Ares where laser was discharged leaving the image on the drum
Negatively charged toner is dispensed on to the drum
Opposites attract so toner is attracted to the positive part of the drum
Toner is applied to the paper by the drum
Paper is heated to fix the toner to the paper

What is secondary storage ?

Used to store files and applications that aren't used regularly

What does a hard disk drive consist of ?

Circular platter which are made from magnetic materials
Actuating arm that hovers above the platter and hold the read write arm
Concentric tracks which are divided into tracks

What does the read / write arm do ?

Changes the magnetic polarity of parts of the tracks to access data in portions of the platter

How can you increase the capacity of a HDD which out increasing the size ?

Adding more platters and decreasing the width of tracks

What does a SSD consist of ?

NAND flash memory cells
Controllers that manage the data

How is data stored in SSD ?

In memory cells which trap electrical charges that hold data. In pages which are combined to form blocks

What is a memory cell ?

Floating gate transistors

How does SSD write data ?

Can't over write so has to erase the data in the page before writing new information

What is an optical disk ?

Stores data on disks which can be read by a laser

How is data written on to a disk ?

A high powered lasers will burn pits into the disk

How is data read on a disk ?

The edge of the pits reflected the light back and this is read as a binary value of 1